Abstract: Springtime composites of surface chlorophyll a (chl) from the SeaWiFS instrument show a sharp increase in chl standing stock (on the order of 0.2 mg m^-3) located between 30°-40°N latitude in the eastern North Pacific Ocean. To investigate the spatial and interannual variability of this springtime feature, multi-platform surveys (23°-33°N, 158°W), including shipboard and satellite measurements, were conducted in April 1998 (El Niño) and 1999 (La Niña) to characterize the hydrographic conditions associated with the large chl gradient. Irradiance and chl data collected during the cruise periods were used in an optical model to compute depth-integrated rates of primary production. The southern portion of both transects resembled the climatological conditions at the Hawaii Ocean Time-series (HOT) study site, Station ALOHA (22.75°N, 158°W), with two major physical and biological frontal features encountered: the South Subtropical Front (SSTF) in 1998 (27°-28°N) and 1999 (32.5°N), and the Subtropical Front (STF) in 1998 (32°N) only; the STF had migrated northward out of our study area in 1999 (~34°N).

Integrated chl and primary production both increased at the frontal locations in both years. Increases in surface chl from SeaWiFS and shipboard measurements were not apparent at the SSTF, yet the subsurface chl maximum both shallowed and doubled at this front. In addition, primary production modeled from the satellite chl data did not reflect the smaller mesoscale variability of the SSTF. The increase in surface chl at the STF, however, was clearly recorded in both the satellite and shipboard chl measurements. HPLC pigment analysis was performed for select samples collected during the El Niño cruise and revealed a change in phytoplankton composition at all frontal locations. Specifically, there were distinct increases in the dinoflagellate marker, peridinin, and the diatom marker, fucoxanthin, at the SSTF. The same patterns at the SSTF were observed during both cruises, except all gradients were shifted to the north due to changes in the large-scale circulation of the gyre in 1999. While the eastern equatorial Pacific experiences a dramatic decrease in chl concentrations during El Niño events, the subtropical Pacific appears to be more 'green' with a southward shift of the circulatory and high surface chl fronts.

Progress in Oceanography. in press, 2001

Abstract: The global continental haze pattern was evaluated based on daily average visibility data at 7000 surface weather stations over five years, 1994-98. The data processing consisted of three broad categories of filters: (1) validity of individual data points, (2) filters based on statistics for specific stations, and (3) filters based on spatial analysis. The data are presented as the aerosol extinction coefficient (Bext or haze) at the surface, seasonally aggregated over five years. The data reveal that the continental haze is concentrated over distinct aerosol regions of the world. The haziest regions of Asia are the Indian subcontinent, eastern China, and Indochina where the 75 percentile seasonal Bext exceeds 0.4 km(-1) In Africa, the highest year around extinction coefficient > 0.4 km(-1) is found over Mauritania, Mall and Niger. During December, January, February, the savanna region of sub-Saharan Africa shows similar values. The haziest region of South America is over Bolivia, adjacent to the Andes mountain range, with a peak during August-November (0.4-0.6 km(-1)). In North America and Europe, there are isolated haze pockets, such as the San Joaquin Valley in California and the Po River Valley in the northern Italy. In many regions of the world the size, shape, and intensity of hazy pockets is determined by the topographic barriers. A major qualification of this work is that the haze maps are based on daily average visibility which emphasizes humid regions with hygroscopic aerosols (nighttime peak Bext) and de-emphasizes arid, dusty regions with daytime maximum extinction. Regional haze episodes over several continental aerosol regions are illustrated by truecolor rendering of the reflectance data from the SeaWiFS satellite.
© 2000 Elsevier Science Ltd. All rights reserved.

ATMOS ENVIRON 34: (29-30) 5067-5078 2000

Key Words: haze, visibility, aerosol, light extinction, scattering efficiency, optical-properties, smoke, brazil, space

Abstract: In the context of the iron hypothesis, the biogeochemical characteristics of the water masses located in the N-E wake of the Kerguelen archipelago were studied in austral spring 1995 during the ANTARES 3/France JGOFS cruise. In agreement with satellite observations (CZCS and SeaWifs data), this cruise showed the surface waters in the wake of the Kerguelen archipelago to be rich in both chlorophyll a and dissolved iron, compared to other observations in the HNLC oceanic waters of the Southern Ocean. This gives support to the hypothesis that natural fertilization due to iron inputs occurs in the waters surrounding the Antarctic Islands. However, the mesoscale structure of the water masses in the study area was complex, and three contrasted zones were identified within the region of lesser or greater iron enrichment. The coastal zone was characterized by very high concentrations of dissolved iron ( > 10 nM) and lithogenic material, but the phytoplankton biomass, dominated by small species, was low. An intrusion of cold Antarctic surface water, rich in silicic acid, was separated from the coastal zone by a shelf-break front. This water tongue contained chlorophyll a concentrations as. low (< 0.3 g 1(-1)) as in the iron-poor open ocean. A third water body, offshore, was characterized by the highest concentrations of phytoplankton (cell abundance and chlorophyll a) and biogenic silica, the community being dominated by large diatoms and dinoflagellates. The distribution of conservative tracers and lithogenic elements, as well as the phytoplankton taxonomic composition, indicate that this offshore water was not derived from a coastal origin. It more likely resulted from the mixing of the Antarctic water tongue Bowing northward along the island continental slope with subantarctic surface water flowing eastward north of the Kerguelen Islands. As regards the interactions between dissolved iron and phytoplankton biomass and growth in surface waters, two typical situations were encountered. Although iron-rich (dissolved Fe > 2 nM), both the coastal zone and the Antarctic water tongue were chlorophyll a poor. This was accounted for by either a heavy grazing pressure exerted by copepods (coastal zone) or an unfavourable light-mixing regime (Antarctic water tongue). In the offshore waters, by contrast, dissolved iron concentrations in the range 0.45-0.7 nM were sufficient to support higher phytoplankton growth under a more favourable light-mixing regime.
© 2000 Elsevier Science Ltd. All rights reserved.

DEEP-SEA RES PT I 48: (1) 163-187 JAN 2001

Key Words: seawater, iron, phytoplankton, equatorial Pacific-Ocean, marine-phytoplankton, fertilization experiment, enrichment experiments, feeding selectivity, antarctic waters, canary-islands, coastal waters, Scotia Seas, Weddell-Sea

Abstract: Increasing evidence suggests that bio-optical properties of Antarctic waters are significantly different than those at temperate latitudes. Consequently, retrieval of chlorophyll concentrations from remotely sensed reflectance measurements using standard ocean color algorithms are likely to be inaccurate when applied to the Southern Ocean. Here we utilize a large bio-optical data set (>1000 stations) collected in waters west of the Antarctic Peninsula in conjunction with the Palmer Long Term Ecological Research program to assess ocean optical properties and associated ocean color algorithms. We find that the remote sensing reflectance spectrum as a function of chlorophyll concentrations appears significantly different from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) Bio-optical Algorithm Mini-workshop data set collected from other regions of the world's oceans. For Antarctic waters, remote sensing reflectance is significantly higher in the blue region and lower in the green region of the spectrum for high chlorophyll concentrations (>1 mg Chi m(-3)). Therefore applying general processing algorithms for both Coastal Zone Color Scanner and SeaWiFS in these Antarctic waters results in an underestimate of chlorophyll by roughly a factor of 2. From modeled estimates of absorption and backscattering we hypothesize that both low chlorophyll-specific absorption and low backscattering contribute to the high reflectance ratios.

J GEOPHYS RES-OCEANS 105: (C11) 26301-26312 NOV 15 2000

Key Words: biooptical properties, diffuse-reflectance, southern-ocean, ice-zone, phytoplankton, sea, bacterioplankton, photosynthesis, variability, scattering

Abstract: We present the results of an experiment designed to measure the changes in the radiometric calibration of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) from the time of its manufacture to the time of the start of on-orbit operations. The experiment uses measurements of the Sun at the manufacturer's facility to predict the instrument outputs during solar measurements immediately after launch. Because an onboard diffuser plate is required for these measurements, the experiment measures changes in the instrument-diffuser system. There is no mechanism in this experiment to separate changes in the diffuser from changes in the instrument. For the eight SeaWiFS bands, the initial instrument outputs on orbit averaged 0.8% higher than predicted with a standard deviation of 0.9%. The greatest difference was 2.1% (actual output higher than predicted) for band 3. The estimated uncertainty for the experiment is 3%. Thus the transfer-to-orbit experiment shows no changes in the radiometric sensitivities of the SeaWiFS bands-at the 3% level-from the completion of the instrument's manufacture to its insertion into orbit.

APPL OPTICS 39: (30) 5620-5631 OCT 20 2000

Key Words: atmospheric correction, sensitivity

Abstract: The current SeaWiFS algorithms frequently yield negative water-leaving radiance values in turbid Case II waters primarily because the water-column reflectance interferes with the atmospheric correction based on the 765-nm and 865-nm spectral bands. Here we present a simple, practical method to separate the water-column reflectance from the total reflectance at 765 nm and 865 nm. Assuming the type of aerosol does not vary much over relatively small spatial scales (similar to 50-100 km), we first define the aerosol type over less turbid waters. We then transfer it to the turbid area by using a "nearest neighbor" method. While the aerosol type is fixed, the concentration can vary. This way, both the aerosol reflectance and the water-column reflectance at 765 nm and 865 nm may be derived. The default NASA atmospheric correction scheme subsequently is used to obtain the aerosol scattering components at shorter wavelengths. This simple method was tested under various atmospheric conditions over the Gulf of Mexico, and it proved effective in reducing the errors of both the water-leaving radiance and the chlorophyll concentration estimates. In addition, in areas where the default NASA algorithms created a mask due to atmospheric correction failure, water-leaving radiance and chlorophyll concentrations were recovered. This method, in comparison with field data and other turbid water algorithms, was tested for the Gulf of Maine and turbid, posthurricane Gulf of Mexico waters. In the Gulf of Maine it provided more accurate retrievals with fewer failures of the atmospheric correction algorithms. In the Gulf of Mexico it provided far fewer pixels with algorithms failure than the other methods, did not overestimate chlorophyll as severely, and provided fewer negative water-leaving radiance values.
© Elsevier Science Inc., 2000.

REMOTE SENS ENVIRON 74: (2) 195-206 NOV 2000

Key Words: zone color scanner, ocean-color

Abstract: The growth of populations is known to be influenced by dispersal, which has often been described as purely diffusive(1,2). In the open ocean, however, the tendrils and filaments of phytoplankton populations provide evidence for dispersal by stirring(3,4). Despite the apparent importance of horizontal stirring for plankton ecology, this process remains poorly characterized. Here we investigate the development of a discrete phytoplankton bloom, which was initiated by the iron fertilization of a patch of water (7 km in diameter) in the Southern Ocean(5). Satellite images show a striking, 150-km-long bloom near the experimental site, six weeks after the initial fertilization. We argue that the ribbon-like bloom was produced from the fertilized patch through stirring, growth and diffusion, and we derive an estimate of the stirring rate. In this case, stirring acts as an important control on bloom development, mixing phytoplankton and iron out of the patch, but also entraining silicate. This may have prevented the onset of silicate limitation, and so allowed the bloom to continue for as long as there was sufficient iron. Stirring in the ocean is likely to be variable, so blooms that are initially similar may develop very differently.

NATURE 407: (6805) 727-730 OCT 12 2000

Key Words: North-Atlantic, southern-ocean, tracer, patchiness, SeaWiFS, evolution

Abstract: Satellite-derived time series for the California Current System (CCS) showed marked changes in the surface chlorophyll a concentration (Chl, mg m(-3)) associated with the 1997-98 El Nino. In addition to the previously known de crease in Chi off Southern California (Fiedler, 1984), we also observed a significant increase of Chi off Baja California. Whereas the extent of eutrophic (Chl > 1.0) areas decreased throughout the CCS, the extent of mesotrophic areas (0.2 < Chi < 1.0) off Baja California approximately doubled. The reduced area of eutrophic waters is attributed to weakened upwelling but the increase in the offshore mesotrophic area off Baja may be caused by blooms of nitrogen-fixing cyanobacteria. Using revised Coastal Zone Color Scanner data we detected similar changes during the 1982-83 El Nino.

GEOPHYS RES LETT 27: (18) 2937-2940 SEP 15 2000

Key Words: satellite-observations, variability, SeaWiFS, ocean

Abstract: A new generation of ocean colour satellites is now operational, with frequent observation of the global ocean. This paper reviews the potential to estimate marine primary production from satellite images. The procedures involved in retrieving estimates of phytoplankton biomass, as pigment concentrations, are discussed. Algorithms are applied to SeaWiFS ocean colour data to indicate seasonal variations in phytoplankton biomass in the Celtic Sea, on the continental shelf to the south west of the UK. Algorithms to estimate primary production rates from chlorophyll concentration are compared and the advantages and disadvantage discussed. The simplest algorithms utilise correlations between chlorophyll concentration and production rate and one equation is used to estimate daily primary production rates for the western English Channel and Celtic Sea; these estimates compare favourably with published values. Primary production for the central Celtic Sea in the period April to September inclusive is estimated from SeaWiFS data to be 102 gC m(-2) in 1998 and 93 gC m(-2) in 1999; published estimates, based on in situ incubations, are ca. 80 gC m(-2). The satellite data demonstrate large variations in primary production between 1998 and 1999, with a significant increase in late summer in 1998 which did not occur in 1999. Errors are quantified for the estimation of primary production from simple algorithms based on satellite-derived chlorophyll concentration. These data show the potential to obtain better estimates of marine primary production than are possible with ship-based methods, with the ability to detect short-lived phytoplankton blooms. In addition, the potential to estimate new production from satellite data is discussed.
© 2000 Elsevier Science BN. All rights reserved.

J EXP MAR BIOL ECOL 250: (1-2) 233-255 JUL 30 2000

Key Words: phytoplankton, primary production, ocean colour satellites, Celtic Sea, Western English Channel, chlorophyll concentration

Abstract: The analysis of thirty-one infrared images from NOAA satellites (September 6-November 14, 1997) revealed the formation and movement of five near-shore anticyclonic eddies (NAEs) within the region between Tuapse and the Kerch Strait during the period from September 6 to October 8. In addition, an area of cold water (zone of divergence) occurred throughout the whole period of observations between the Rim Current and the anticyclones in the center of the eastern part of the Black Sea. This zone included one or two cyclones with diameters of about 40 km. The temperature contrast between this zone and the warm near-shore flow was as high as 6.5 degrees C. Over some parts of the trajectory, the velocity of the movement of the NAEs about 40 km in diameter was as high as 15 cm/s. The transformation of an NAE formed west of Novorossiisk into a deep-sea eddy was traced. The hydrographic measurements from RN Akvanavt (November 12-15, 1997) revealed the surfacing of the isopycnals within the zone of divergence and their deepening toward the center of the eastern basin. Increased chlorophyll a concentrations las compared with the mean concentration in the center of the eastern part of the sea) were noted on October 8, 1997 from the data of the SeaWiFS radiometer in four "young" NAEs and in the zone of divergence. A reduced chlorophyll a concentration occurred in the "old" NAE tone month old) transformed into an open-sea eddy.

OCEANOLOGY+ 40: (3) 316-328 MAY-JUN 2000

Key Words: deep regions, satellite, patterns, currents

Abstract: Validation of the atmospheric correction and biooptical algorithms of the SeaWiFS satellite scanner was performed using direct comparison between the satellite and in situ data obtained during the scientific cruise of RN Akvanavt in the Black and Aegean seas in October 1997, First, it was verified whether the radiation values at the top of the atmosphere measured with the SeaWiFS sensor and calculated by the Monte Carlo technique from the data of field observations were in agreement. Then, the SeaWiFS atmospheric correction algorithm was verified by comparing the values of the normalized radiation from the water surface and aerosol optical thickness derived from the SeaWiFS data and field measurements in situ, The authors proposed an analytical algorithm for the determination of the chlorophyll concentration along with the standard SeaWiFS algorithm, A comparison of the results obtained using both of the algorithms with the values measured in situ shows that the algorithm suggested by the authors is in reasonable agreement in all the cases studied, whereas the SeaWiFS algorithm can lead to a significant overestimation of the chlorophyll concentration for waters with a predominance of absorption by the yellow substance.

OCEANOLOGY+ 40: (3) 329-334 MAY-JUN 2000

Key Words: water

Abstract:Spatial inhomogeneity, or speckling, frequently occurs in Sea-viewing Wide Field-of-view Sensor (Sea-WiFS) data products such as water-leaving radiance and chlorophyll concentration. We have found that this effect may be caused by high-altitude aerosols or thin cirrus clouds or even by digitization errors. For the scenes evaluated, whitecaps were ruled out as a likely cause of these errors. We tried to avoid using the 765-nm band, which is affected by O-2 absorption and is more sensitive to digitization errors, by instead using the 670-nm band in the atmospheric correction and found that speckling for either cloud-free areas or cloud-adjacent areas was significantly reduced.
© 2000 Optical Society of America OCIS codes: 280.0280, 280.1310.

APPLIED OPTICS 39: (21) 3573-3581 JUL 20 2000

Key Words:ZONE COLOR SCANNER, RADIANCES, SYSTEM

Abstract: The assumption that values of water-leaving radiance in the near-infrared (NIR) are negligible enable aerosol radiative properties to be easily determined in the correction of satellite ocean color imagery. This is referred to as the black pixel assumption. We examine the implications of the black pixel assumption using a simple bio-optical model for the NIR water-leaving reflectance [rho(omega)(lambda(NIR))](N). In productive waters [chlorophyll (Chl) concentration >2 mg m(-3)], estimates of [rho(omega)(lambda(NIR))](N) are several orders of magnitude larger than those expected for pure seawater. These large values of [rho(omega)(lambda(NIR))](N) result in an overcorrection of atmospheric effects for retrievals of water-leaving reflectance that are most pronounced in the violet and blue spectral region. The overcorrection increases dramatically with Chl, reducing the true water-leaving radiance by roughly 75% when Chi is equal to 5 mg m(-3). Relaxing the black pixel assumption in the correction of Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) satellite ocean color imagery provides significant improvements in Chl and water-leaving reflectance retrievals when Chi values are greater than 2 mg m(-3). Improvements in the present modeling of [rho(omega)(lambda(NIR))](N) are considered, particularly for turbid coastal waters. However, this research shows that the effects of nonzero NIR reflectance must be included in the correction of satellite ocean color imagery.
© 2000 Optical Society of America OCIS codes: 010.0010, 280.0280, 010.4450.

APPLIED OPTICS 39: (21) 3582-3591 JUL 20 2000

Key Words: water-leaving radiance, diffuse transmittance, case-1 waters, scattering, SeaWiFS, coastal, sensors, light, absorption, dependence

Abstract:The primary objective of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) Project is to produce water-leaving radiances within an uncertainty of 5% in clear-water regions, and chlorophyll a concentrations within 35% over the range of 0.05-50 mg m(-3). Any global mission, like SeaWiFS, requires validation data from a wide variety of investigators. This places a significant challenge on quantifying the total uncertainty associated with the in situ measurements. because each investigator follows slightly different practices when it comes to implementing all of the steps associated with collecting field data, even those with a prescribed set of protocols. This study uses data from multiple cruises to quantify the uncertainties associated with implementing data collection procedures while using different in-water optical instruments and deployment methods. A comprehensive approach is undertaken and includes (a) the use of a portable light source and in water intercomparisons to monitor the stability of the field radiometers, (b) alternative methods for acquiring reference measurements, and (c) different techniques for making in-water profiles. Three optical systems had quadrature sum uncertainties sufficiently small to ensure a combined uncertainty for the spaceborne and in situ measurements within a total 5% vicarious calibration budget. A free-fall profiler using (relatively inexpensive) modular components performed best (2.7% quadrature sum uncertainty), although a more sophisticated (and comparatively expensive) profiler using integral components was very close and only 0.5% higher. A relatively inexpensive system deployed with a winch and crane was also close, but ship shadow contamination increased the quadrature sum uncertainty to approximately 3.4%.

JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY

Key Words:SeaWiFS,quality monitor, field radiometers, light-source, SQM

Abstract: The space-rime variation of phytoplankton pigments in the western Intra-Americas Sea (IAS), in the vicinity of the island of Cuba, is examined using digital images obtained with the Coastal Zone Color Scanner sensor flown aboard the Nimbus 7 satellite from 1978 to 1986. The results are compared to historical in situ hydrographic observations. A marked seasonality in pigment concentration was observed in waters around Cuba, with an average of 0.07 mg m(-3) in summer (April-September) and 0.13 mg m-3 during winter (October-March). The range of variation in pigment concentration was larger in the Gulf of Mexico relative to the western Caribbean Sea. We identified four biogeographical areas on the basis of groups of pixels with similar patterns of time variability. These are area I: southwest of Cuba, Yucatan Channel, and Florida Strait; area II: central Gulf of Mexico; area III: east of Cuba; and area IV: central Caribbean Sea, south of Jamaica and Hispaniola. Two major meteorological events led to anomalies in the seasonal cycle of pigment concentrations. During El Nino-Southern Oscillation (ENSO) of 1982-1983, positive anomalies were observed in the pigment concentration in the western IAS during winter months. This was associated with intense mixing of the water column by higher-frequency and stronger winds associated with cold fronts. ENSO 1952-1983 therefore had a fertilizing effect on the IAS region. Another positive anomaly was observed in 1980-1981, a non-ENSO period that featured higher hurricane and extratropical low-pressure activity.

JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 105: (C6) 14029-14043 JUN 15 2000

Key Words: ocean color, southern oscillation, Caribbean Sea, Gulf, radiance, patterns, SeaWiFS, Mexico, CZCS, time

Abstract: Nine juvenile loggerhead sea turtles tracked during 1997 and 1998 in the central North Pacific by satellite telemetry all travelled westward, against prevailing currents, along two convergent fronts identified by satellite remotely sensed data on sea surface temperature (SST), chlorophyll and geostrophic currents. These fronts are characterized by gradients in sea surface height that produce an eastward geostrophic current, with gradients in surface chlorophyll and SST. Six of the turtles were associated with a front characterized by 17 degrees C SST, surface chlorophyll of about 0.2 mg m(-3), and eastward geostrophic current of about 4 cm s(-1), while the other three turtles were associated with a front with 20 degrees C SST, surface chlorophyll of about 0.1 mg m(-3), and eastward geostrophic flow of about 7 cm s(-1). These results appear to explain why incidental catch rates of loggerheads in the Hawaii longline fishery are highest when gear is set at 17 degrees C and 20 degrees C, SST. Further, from the seasonal distribution of longline effort relative to these fronts, it appears that the surface longline fishing ground lies largely between these two fronts during the first quarter and well to the south of the 17 degrees C front, but including the 20 degrees C front, in the second quarter. These findings suggest seasonal or area closures of the longline fishery that could be tested to reduce incidental catches of loggerheads. Finally, these results illustrate the insights which can be achieved by combining data on movement of pelagic animals with concurrent remotely sensed environmental data.

FISHERIES OCEANOGRAPHY 9: (1) 71-82 MAR 2000

Key Words:SeaWiFS, Hawaii

Abstract: The Atlantic Meridional Transect programme uses the twice-annual passage of the RRS James Clark Ross between the UK and the Falkland Islands. before and after the Antarctic research programme in the Austral Summer (see Aiken, J., & Bale, A. J. (2000). An introduction to the Atlantic Meridional Transect (AMT) Programme. Progress in Oceanography, this issue). This paper examines the scientific rationale for a spatially-extensive time and space series programme and reviews the relevant physical and biological oceanography of the Atlantic Ocean. The main scientific observations from the research programme are reported. These are set in the context of historical and contemporary observations pertinent to the principal objectives, of the cruise, notably the satellite remotely sensed observations of ocean properties. The extent to which the programme goals have been realised by the research to date is assessed and discussed. New bio-optical signatures, which can be related to productivity parameters, have been derived. These can be used to interpret remotely sensed observations of ocean colour in terms of productivity and production processes such as the air/sea exchange of biogenic gases, which relate to the issues of climate change and the sustainability of marine ecosystems.
© 2000 Elsevier Science Ltd. All rights reserved.

PROGRESS IN OCEANOGRAPHY 45: (3-4) 257-312 2000

Key Words: equatorial pacific-ocean, north-atlantic, phytoplankton photosynthesis, water masses, SeaWiFS, variability, circulation, climate, JGOFS, iron

Abstract: We present an overview of the spatial distributions of phytoplankton pigments along transects between the UK and the Falkland Islands. These studies, undertaken as a component of the UK Atlantic Meridional Transect (AMT) programme, provided the first post-launch validation data for the NASA SeaWiFS satellite. Pigment data are used to characterise basin-scale variations in phytoplankton biomass and community composition over 100 degrees of latitude, and to compliment the definition of hydrographic oceanic provinces. A summary of the key pigment characteristics of each province is presented.

Concentrations of total chlorophyll a (totCHLa = chlorophyll a, CHLa + divinyl CHLa, dvCHLa) were greatest in high latitude temperate waters (>37 degrees N and >35 degrees S), and in the Canary Current Upwelling system. In these regions, the total carotenoid (totCAR) budget was dominated by photosynthetic carotenoids (PSCs). High accessory pigment diversity was observed of which fucoxanthin (FUC), 19'-hexanoyloxyfucoxanthin (HEX), and diadinoxanthin (DIAD) were most abundant, indicating proliferation of large eukaryotes and nanoflagellates. In contrast, tropical and sub-tropical waters exhibited concentrations of totCHLa below 500 ng 1(-1), with the North Atlantic Sub-tropical East gyre (NASE, 26.7-35 degrees N), South Equatorial Current (SeqC, 7-14.6 degrees S) and South Atlantic tropical Gyre (SATG, 14.6-26 degrees S) characterised by totCHLa of <100 ng(-1). These waters exhibited relatively limited pigment diversity, and the totCAR budget was dominated by photoprotecting pigments (PPCs) of which zeaxanthin (ZEA), a marker of prokaryotes (cyanobacteria and prochlorophytes), was most abundant. DVCHLa, a marker of prochlorophytes was detected in waters at temperatures >15 degrees C, and between the extremes of 48 degrees N and 42 degrees S. DvCHLa accounted for up to two-thirds of totCHLa in oligotrophic provinces demonstrating the importance of prochlorophytes to oceanic biomass.

Overall, HEX was the dominant PSC, contributing up to 75% of totCAR. HEX always represented >2% of totCAR and was the only truly ubiquitous carotenoid. Since HEX is a chemotaxonomic marker of prymnesiophytes, this observation reflects the truly cosmopolitan distribution of this algal class. ZEA was found to be the most abundant PPC contributing more than one third of the total carotenoid budget in each transect.Greatest seasonality was observed in highly productive waters at high latitudes and in shallow continental shelf waters and attributed to proliferation of large eukaryotes during spring. Concentrations of the prokaryote pigments (ZEA + dvCHLa) also exbibited some seasonality, with elevated concentrations throughout most of the transect during Northern Hemisphere spring.
© 2000 Elsevier Science Ltd. All rights reserved.

PROGRESS IN OCEANOGRAPHY 45: (3-4) 339-368 2000

Key Words: subtropical north-atlantic, divinyl chlorophyll-a, marine-phytoplankton, mediterranean-sea, prochlorococcus, HPLC, prochlorophyte, azores, light, zone

Abstract: The Sea-viewing Wide Field-of-view Sensor (SeaWiFS) is the successor ocean color imaging system to the Nimbus-7 Coastal Zone Color Scanner (CZCS). The SeaWiFS calibration and validation effort includes spacecraft, atmospheric, sea surface, subsurface (or in situ), plus laboratory and data analysis components which require pre- and postlaunch activities. The most important goals of this effort are to produce water-leaving radiances with an uncertainty of 5% in clear-water regions and chlorophyll a concentrations within +/-35% over the range of 0.05-50 mg m(-3). The first objective requires field instruments with a calibration and measurement capability on the order of 1%; because these challenging in situ measurements will be acquired from a variety of field instruments over the five-year mission interval, a measurement assurance program is required. This program consists of several activities: an accurate pre launch characterization and calibration of the SeaWiFS instrument; a Marine Optical Buoy (MOBY) rotation in clear water to provide a water-leaving radiance time series for postlaunch vicarious calibration: the SeaWiFS Bio-Optical Archive and Storage System (SeaBASS) to hold the relevant data; clearly defined SeaWiFS Ocean Optics Protocols (SOOP) for established data collection methodologies; annual SeaWiFS Intercalibration Round-Robin Experiments (SIRREXs) for intercomparing field and calibration equipment, and training scientific personnel; direct comparison to a national standard laboratory using the SeaWiFS Transfer Radiometer (SXR); a portable field source, called the SeaWiFS Quality Monitor (SQM), for monitoring the temporal stability of the calibration of field instruments; a highly accurate atmospheric correction algorithm designed for the SeaWiFS instrument response functions; bio-optical algorithms that encompass a broad range of bio-optical provinces; and satellite data processing, duality control, and analysis procedures for monitoring the postlaunch performance of the sensor and the validity of the derived products. The culmination of many of these activities is the deployment of the instruments and methodologies on Atlantic Meridional Transect (AMT) cruises between England and the Falkland Islands, a 13 000 km voyage spanning more than 100 degrees of latitude, with a calibration and measurement accuracy that is on the order of 1%. The AMT Program is the primary product validation activity supported by the SeaWiFS Project The AMT cruises also serve as a testbed for new technology development and have demonstrated that high quality bio-optical data can be routinely provided to the Project in near-real time.

PROG OCEANOGR 45: (3-4) 427-465 2000

Key Words:zone color scanner, quality monitor sqm, ocean-color, atmospheric correction, field radiometers, imagery, sensors, phytoplankton, algorithm, pigment

Abstract: Solar eclipses evident in short wavelength data sensed by polar orbiting Sun-synchronous wide field of view instruments such as SeaWiFS and POLDER are illustrated, and some implications for global dataset production are considered.

INTERNATIONAL JOURNAL OF REMOTE SENSING 21: (9) 1961-1967 JUN 15 2000

Key Words: AVHRR Data, vegetation, index, land, NDVI

Abstract: Sea ice monitoring and forecasting in the Bohai Sea is an operational task of the National Research Center for Marine Forecasts (NRCMEF), China. An overview of current Satellite image receiving and processing systems at NRCMEF in relation to the Bokai Sea ice monitoring, including the use of NOAA-AVHRR, GMS, SAR of ERS-1, Radarsat, and SeaWiFS data, is presented.

JOURNAL OF COLD REGIONS ENGINEERING 14: (2) 93-100 JUN 2000

Abstract: The East China Sea is a typical case 2 water environment, where concentrations of phytoplankton pigments, suspended matter, and chromophoric dissolved organic matter (CDOM) re all higher than those in the open oceans, because of the discharge from the Yangtze River and the Yellow River. By using a hyperspectral semianalytical model, we simulated a set of remote-sensing reflectance for a variety of chlorophyll, suspended matter, and CDOM concentrations. From this simulated data set, a new algorithm for the retrieval of chlorophyll concentration from remote-sensing reflectance is proposed. For this method, we took into account the 682-nm spectral channel in addition to the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) channels. When this algorithm was applied to a field data set, the chlorophyll concentrations retrieved through the new algorithm were consistent with field measurements to within a small error of 18%, in contrast with that of 147% between the SeaWiFS ocean chlorophyll 2 algorithm and the in situ observation. (C) 2000 Optical Society of America OCIS codes: 010.4450, 280.0280.

APPLIED OPTICS 39: (15) 2467-2474 MAY 20 2000

Key Words: dissolved organic-matter, ocean color, waters, absorption, model, coastal, nm

Abstract: Primary productivity and associated biogeochemical fluxes within the Southern Ocean are globally significant, sensitive to change and poorly known compared to temperate marine ecosystems. We present seasonal time series data of chlorophyll a, primary productivity and in-water irradiance measured in the coastal waters of the Western Antarctica Peninsula and build upon existing models to provide a more optimum parameterization for the estimation of primary productivity in Antarctic coastal waters. These and other data provide strong evidence that bio-optical characteristics and phytoplankton productivity in Antarctic waters an different from temperate waters. For these waters we show that over 60% of the variability in primary production can be explained by the surface chlorophyll a concentration alone, a characteristic, which lends itself to remote sensing models. if chlorophyll a concentrations are accurately determined, then the largest source of error 13-18) results from estimates of the photoadaptive variable (P-opt(B)). Further, the overall magnitude of P-opt(B) is low (median 1.09 mg C mg chl(-1) h(-1)) for these data compared to other regions and generally fits that expected for a cold water system. However, the variability of P-opt(B) over the course of a season (0.4 to 3 mg C mg chl(-1) h(-1)) is not consistently correlated with other possible environmental parameters, such as chlorophyll, sea surface temperature, incident irradiance, day length, salinity, or taxonomic composition. Nonetheless, by tuning a standard depth- integrated primary productivity model to fit representative P-opt(B) values and the relatively uniform chlorophyll-normalized production profile found in these waters, we can improve the model to account for approximately 72-73% variability in primary production both for our data as well as for independent historic Antarctic data.

ANTARCTIC SCIENCE 12: (1) 20-32 MAR 2000

Key Words: oceanic primary production, chlorophyll, phytoplankton, photosynthesis, variability, light, biomass, scales, zone, Antarctic Peninsula, bio-optical model, Palmer LTER, primary production, SeaWiFS, Southern Ocean.

Abstract: The proverbial blue colour of the Mediterranean reflects some of the most extreme oligotrophic waters in the world. Sea-surface Sea-viewing Wide Field-of-view Sensor (SeaWiFS) satellite data show the relatively clear, pigment poor, surface waters of the Mediterranean with a generally increasing oligotrophy eastward, apparent even from space. Integrated over depth, however, the east and west Mediterranean show similar amounts of phytoplankton and bacterial biomass. By contrast, primary production and bacterial production are 2 to 3 times lower in the eastern Mediterranean than in the west. However, the relationship between bacterial production and primary production in the east and west are significantly different. While bacterial production is directly proportional to primary production in the east, in the west it increases as approximately the square root of primary production. This suggests that the bacteria in the west are relatively decoupled from local contemporaneous primary production. In contrast, the gradient of close to 1 in the log bacterial production versus log primary production relationship in the east suggests less temporal decoupling and, therefore, less seasonal accumulation of DOG. In addition, the constant proportionality between bacterial and primary production of 0.22, which, if all primary products are respired, gives an estimated geometric mean bacteria growth efficiency of 22 % (95 % confidence limits of 17 and 29 %) for data in the eastern Mediterranean. Our data suggest that the degree of bacteria-phytoplankton coupling has an important effect on apparent trends between bacterial and phytoplankton production in high frequency data. The combination of low primary production and bacterial dominance of secondary production in the east is also of significance as it could account for the low fisheries production, the low vertical flux of material and low biomass of benthic organisms in the region.

MARINE ECOLOGY-PROGRESS SERIES 193: 11-18 2000

Key Words: bacteria, phytoplankton, bacterial growth efficiency, ocean productivity, oligotrophy, Mediterranean dissolved organic-carbon, microbial loop, bacterioplankton, respiration, chlorophyll, phosphorus, ecosystems, limitation, nitrogen, balance.

Abstract: The Earth Observation Application Department at ESRIN is responsible for the operation of the ERS-1 and ERS-2 ground segment, as well as performing operations for non-ESA Earth-observation missions such as for Spot, Landsat, NOAA, SeaWiFS, etc. The ERS ground segment also includes a component - the national and the foreign stations network - which is not directly operated by ESA, but relies on international agreements for data acquisition, processing and distribution.

ESA BULLETIN-EUROPEAN SPACE AGENCY (101) 25-+ FEB 2000

Abstract: The global distribution of aerosol radiative forcing is a large uncertainty in present climate models. Aerosol retrieval from spaceborne sensors can help to fill this gap at least over the ocean. For present satellite sensors like AVHRR, MOS, SeaWiFS or POLDER and future sensors, such as MERIS, MODIS and GLI, algorithms have been developed to derive optical and physical aerosol parameters like optical depth, particle size distribution or aerosol type. Different authors proposed to derive the climatically important aerosol effect on the upward radiative flux directly from satellite measurements of upward radiance instead of deriving aerosol parameters subsequently used for the assessment of the aerosol radiative forcing. By such an approach, retrieval errors due to absorption and not well defined phase functions can be reduced. In this paper, two different algorithms for the direct retrieval of the top of atmosphere upward radiative Aux in the solar spectral region over the ocean are compared. Based on radiative transfer calculations, a regression algorithm and a Neural Net algorithm have been developed for the use of present MOS and future MERIS measurements. Sensitivity tests according to sensor noise were performed for both algorithms. The low noise sensitivity of the Neural Net algorithm makes this type of algorithm more promising. The retrieval scheme is applied to MOS scenes of the North Sea and the North Atlantic.
© 2000 ELSEVIER Science Ltd. All rights reserved.

PHYSICS AND CHEMISTRY OF THE EARTH PART B-HYDROLOGY OCEANS AND ATMOSPHERE 25: (2) 101-106, 2000

Key Words: Greenhouse Gases, Climate

Abstract: The standard SeaWiFS atmospheric correction algorithm, designed for open ocean water, has been extended for use over turbid coastal and inland waters. Failure of the standard algorithm over turbid waters can be attributed to invalid assumptions of zero water-leaving radiance for the near-infrared bands at 765 and 865 nm. In the present study these assumptions are replaced by the assumptions of spatial homogeneity of the 765:865-nm ratios for aerosol reflectance and for water-leaving reflectance. These two ratios are imposed as calibration parameters after inspection of the Rayleigh-corrected reflectance scatterplot. The performance of the new algorithm is demonstrated for imagery of Belgian coastal waters and yields physically realistic water-leaving radiance spectra. A preliminary comparison with in situ radiance spectra fbr the Dutch Lake Markermeer shows significant improvement over the standard atmospheric correction algorithm. An analysis is made of the sensitivity of results to the choice of calibration parameters, and perspectives for application of the method to other sensors are briefly discussed.
© 2000 Optical Society of America.

APPLIED OPTICS 39: (6) 897-912 FEB 20 2000

Key Words: Case-II Waters, Ocean-Color, Optical-Properties, Suspended Matter, Leaving Radiance, CZCS Imagery, Algorithm, Phytoplankton, Chlorophyll, Scattering

Abstract: A neural network methodology is developed to estimate the near-surface phytoplankton pigment concentration of case I waters from spectral marine reflectance measurements (ocean color) at the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) visible wavelengths, The advantages of neural network approximation, i.e., association of nonlinear complexity, smoothness, and reduced sensitivity to noise, are demonstrated. When applied to in situ California Cooperative Oceanic Fisheries Investigations data, the neural network algorithm performs better than the reflectance ratio algorithms. Relative rms errors on pigment concentration are reduced from 61 and 62 to 38%, and absolute rms errors are reduced from 4.43 and 3.52 to 0.83 mg m(-3). When applied to SeaWiFS-derived imagery, there is statistical evidence that the neural network algorithm filters residual atmospheric correction errors more efficiently than the standard SeaWiFS bio-optical algorithm.

JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 105: (C2) 3483-3495 FEB 15 2000

Key Words: Ocean Color, Diffuse-Reflectance, Waters, Spectra, Photosynthesis, Variability,Retrieval, Algorithm, Radiance, SeaWiFS

Abstract: We have examined the seasonality of phytoplankton in the western and northern Bay of Bengal using shipboard data collected during three seasons as well as ocean colour imagery from OCTS and SeaWiFS. Seasonal changes in the hydrography of the bay observed during these seasons gave rise to striking differences in biomass and primary productivity. Heavy fresh water influx from rivers and the resulting vertical stratification impeded vertical transfer of nutrients. Although such a nutrient regime resulted in a oligotrophic environment, chlorophyll a and primary production were substantially enhanced by physical processes that could erode the strong halocline. In March-April (pre-southwest monsoon), the poleward flowing East India Coastal Current brought to the surface, nutrient laden cooler waters that enriched the coastal region, but highest biomass (Chl a, 53 mg m(-2)) and productivity (4.5 g C m(-2) d(-1)) were in the region of an eddylike structure along the coast and in the region between 13 degrees and 16 degrees N lat. Its appearance in satellite images of two consecutive years suggests the structure to be an annual feature. Wind driven coastal upwelling and increased river runoff during the following season, the southwest monsoon (July-August), increased phytoplankton biomass dramatically (92 mg m(-2)) but productivity averaged only 0.3 g C m(-2) d(-1) suggesting light limitation due to intense cloud cover. With a reduction in cloud cover and enhanced irradiance during the following season, the northeast monsoon (January-February), primary production increased especially in the northern part of the bay where phytoplankton appeared to benefit from both improved light conditions and nutrient inputs from estuarine mechanisms and river runoff.
© 2000 Elsevier Science Ltd. All rights reserved.

CONTINENTAL SHELF RESEARCH 20: (3) 313-330 FEB 2000

Key Words: Physical Processes, River Discharge, Phytoplankton Biomass, Productivity, Bay Of Bengal, Western Boundary Current, Marine-Phytoplankton, Natural Assemblages, Northeast Monsoon, Indian-Ocean, Arabian Sea, Photosynthesis, Productivity, Southwest, Biomass

Abstract: The modular optoelectronic scanner (MOS) is a German instrument that was launched in the spring of 1996 on the Indian IRS-P3 satellite. With the successful launch of NASA's Sea-viewing Wide Field-of-view Sensor (SeaWiFS) in the summer of 1997, there are non two ocean color missions in concurrent operation, and there is interest within the scientific community to compare data from these two sensors. In this paper, we describe our efforts to retrieve ocean-optical properties from both SeaWiFS and MOS using consistent methods. We first briefly review the atmospheric correction, which removes more than 90% of the observed radiances in the visible, and then we describe how the atmospheric-correction algorithm used for the SeaWiFS data can be modified for application to other ocean color sensors. Next, since the retrieved water-leaving radiances in the visible between MOS and SeaWiFS are significantly different, we developed a vicarious intercalibration method to recalibrate the MOS spectral bands based on the optical properties of the ocean and atmosphere derived from the coincident SeaWiFS measurements. Furthermore, because of the strange calibration behavior of the MOS 750 nm band, we modified the atmospheric correction such that the MOS 685 and 868 nm bands can also be used. We present and discuss the MOS-retrieved, ocean-optical properties before and after the vicarious calibration using both the MOS 685 and 750 nm coupled with 868 nm bands in comparison with results from SeaWiFS and demonstrate the efficacy of this approach. We show that it is possible and efficient to vicariously intercalibrate sensors between one and another.

IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING 38: (1) 184-197, Part 1 JAN 2000

Key Words: Atmospheric Correction, Ocean Color, Remote Sensing, Vicarious Calibration, Water-Leaving Radiance, Atmospheric Correction, Algorithm, Imagery, Sensors

Correction
No Abstract Available

JOURNAL OF THE MARINE BIOLOGICAL ASSOCIATION OF THE UNITED KINGDOM 79: (6) 1156-1156 DEC 1999

Abstract: Three independent ocean color sampling methodologies are compared to assess the potential impact of instrumental characteristics and environmental variability on shipboard remote-sensing reflectance observations from the Santa Barbara Channel, California. Results indicate that under typical field conditions, simultaneous determinations of incident irradiance can vary by 9-18%, upwelling radiance just above the sea surface by 8-18%, and remote-sensing reflectance by 12-24%. Variations in radiometric determinations can be attributed to a variety of environmental factors such as Sun angle, cloud cover, wind speed, and viewing geometry; however, wind speed is isolated as the major source of uncertainty. The above-water approach to estimating water-leaving radiance and remote-sensing reflectance is highly influenced by environmental factors. A model of the role of wind on the reflected sky radiance measured by an above-water sensor illustrates that, for clear-sky conditions and wind speeds greater than 5 m/s, determinations of water-leaving radiance at 490 nm are undercorrected by as much as 60%. A data merging procedure is presented to provide sky radiance correction parameters for above-water remote-sensing reflectance estimates. The merging results are consistent with statistical and model findings and highlight the importance of multiple field measurements in developing quality coastal oceanographic data sets for satellite ocean color algorithm development and validation.
© 2000 Optical Society of America OCIS codes: 010.4450, 280.0280.

APPLIED OPTICS 39: (3) 456-469 JAN 20 2000

Key Words: SeaWiFS, Waters, Chlorophyll, Algorithms, Color

Abstract: The atmospheric aerosol effect makes an important contribution to the total radiance in the visible and infrared bands, observed by the Ocean Color Imager on the ROCSAT-1 satellite. For better interpretations of OCI data, an accurate aerosol effect correction is necessary. In this study the concept of clear water is adopted to determine the aerosol effect as part of the atmospheric effect correction model, OCITRAN-1, A clear water area is chosen to assess the aerosol condition and remove the aerosol effect. Two SeaWiFS image sets were used to test the accuracy of the OCITRAN-1 model by comparing its result with those obtained by the SeaDAS model. The comparison shows a reasonable consistency between the estimates generated by these two models in low chlorophyll concentration areas, but the water leaving radiance derived by OCITRAN-1 is significantly greater than that derived by SeaDAS, especially when the chlorophyll concentration is higher than 2.0 mg/m(3), Therefore, the aerosol effect correction of OCITRAN-1 is most suitably applied in ocean areas of low chlorophyll concentration.

TERRESTRIAL ATMOSPHERIC AND OCEANIC SCIENCES 10: (4) 855-864 DEC 1999

Key Words: OCI, Atmospheric Correction, Aerosol Effect, Coastal Zone Color Scanner, Algorithm, System

Abstract: With the successful launch of the first scientific satellite of the Republic of China (ROCSAT-1) on 27 January 1999, Taiwan enters the era as a satellite data providing country. There are three scientific payloads on the satellite. One of them is the Ocean Color Imager (OCI). OCI is a push-broom reflective imager for monitoring ocean colors. OCI has taken images since March 1999. Because there is no on-board calibrator on OCI, a comparison with Sea-viewing Wide Field-of-view Sensor (SeaWiFS) data was performed in order to validate OCI data. Simultaneously in-situ observations of optical properties and chlorophyll a concentration were also collected in waters adjacent to Taiwan for vicarious calibration. We applied SeaWiFS atmospheric correction and bio-optical algorithms on OCI data to derive normalized water-leaving radiance and chlorophyll a concentration. Results show that the chlorophyll a concentration derived from OCI is generally larger than that derived from SeaWiFS. The correlation coefficient is about 0.60 with a root-mean-squared (RMS) of difference of chlorophyll a concentration of 0.10 mg/m(3).

TERRESTRIAL ATMOSPHERIC AND OCEANIC SCIENCES 10: (4) 873-883 DEC 1999

Key Words: OCI, SeaWiFS, Validation, Ocean Color, SIMBIOS, Atmospheric Correction

Abstract: The magnitude of El Nino in 1997-98 was one of the strongest of the century. A series of red tides occurred in Hong Kong territorial waters between mid-March and mid-April 1998, resulting in the loss of HK$250 (US$32) million in fish kill damage. The causative species was Gyrodinium auteolum. We used a time series of satellite images to track the development of the harmful algal bloom and relate its movement to physical oceanographic conditions. Prior to the red tide event in Hong Kong, harmful algal blooms had occurred earlier (November 1997-February 1998) along the south China coast to the east of Hong Kong, although the species were different. The progression of harmful algal blooms from northeast to southwest coincided with the southwesterly movement of the south China Coastal Current as indicated by the satellite images of SST (sea surface temperature) from the satellite AVHRR. Remote sensing images of chlorophyll a (chl a) from SeaWiFS (sea-viewing wide field of view sensor) confirmed high near-shore chi a for the same region. The entire event coincided with the dramatic change in the oceanographic conditions of the northern portion of the South China Sea between 1997 and 1998 for the period of March to mid-April, as revealed in the weekly composite SST. The SST images showed a warm tongue pointing north to the south China coast in 1998 versus a cold tongue pointing south in 1997 in the middle of the South China Sea. The differences are believed to be due to El Nino and responsible for setting up the physical oceanographic conditions which were favorable for the formation of harmful algal blooms along the south China coast. The warm tongue in SST suggested that the warm water from the South China Sea might have been piling up towards the south China coast. On the other hand, downwelling of the south China Coastal Current along the coast due to the Northeast Monsoon during March might have been moving against the South China Sea warm water at the bottom. As a result, the coastal waters of the south China coast including Hong Kong became trapped along the coast. Given local eutrophied conditions of the China coast, the outbreak of harmful algal blooms occurred over a coast-wide scale (similar to 400 km) in winter 1997 and spring 1998. It appears that the use of satellite SST images is helpful in detecting large-scale changes in oceanographic conditions and relating the changes to possible outbreak of harmful algal blooms.

MARINE ECOLOGY-PROGRESS SERIES 187: 289-294 1999

Key Words: Red Tides, El Niño, South China Sea, Satellite Images, SeaWiFS, Consequences, Blooms

No Abstract Availible

INTERNATIONAL JOURNAL OF REMOTE SENSING 20: (17) 3243-3244 NOV 20 1999

Abstract: Most of the existing satellite sensors lack the spectral capabilities to discriminate phytoplankton pigments in water bodies. New satellite sensors (i.e. SeaWIFS) and future sensors on board EOS with narrow bandwidths will provide fine spectral resolution necessary to distinguish optical properties of nearshore waters provided sea data are available. This will enable spaceborne water color sensors to discriminate bloom forming phytoplankton species. The objective was to develop a library of absorption spectra for the most common phytoplankton species found within the Hudson/Raritan Estuary and coastal waters of New Jersey. Both culture-grown and field samples of phytoplankton were concentrated and analyzed using chemical and spectrometric techniques. Using spectral derivative and polynomial regression analysis, it was possible to identify wavelengths that could be used to characterize the pigment compositions of phytoplankton species in the estuary.

INTERNATIONAL JOURNAL OF REMOTE SENSING 20: (17) 3393-3397 NOV 20 1999

Abstract: A new empirical chlorophyll algorithm is proposed for SeaWiFS (Sea-viewing Wide Field-of-view Sensor) and other ocean colour sensors. The CAL-P6 algorithm uses a sixth-order polynomial of the ratio of normalized water leaving radiances (L-WN) at 490 nm and 555 nm and is based on 348 measurements of L-WN,, and chlorophyll-a in the California Current. Validation of the SeaWiFS-derived chlorophyll values with 27 concurrent in situ measurements showed high correlation (r(2) = 0.93 in the log-log space) but significant overestimation by SeaWiFS at high chlorophyll-a concentration. The problem was traced to significant underestimation of the SeaWiFS-derived L-WN,, (490) at high chlorophyll-a concentration (3-5mgm(-3)). Further refinement of the atmospheric correction is needed for SeaWiFS to attain its goal of 35% accuracy for chlorophyll retrieval in the coastal zone.

INTERNATIONAL JOURNAL OF REMOTE SENSING 20: (17) 3423-3429 NOV 20 1999

Key Words: Ocean Color

Abstract: The position and structure of the North Atlantic Subtropical Front is studied using Lagrangian flow tracks and remote sensing (AVHRR imagery: TOPEX/POSEIDON altimetry: SeaWiFS) in a broad region (similar to 31 degrees to similar to 36 degrees N) of marked gradient of dynamic height (Azores Current) that extends from the Mid-Atlantic Ridge (MAR), near similar to 40 degrees W, to the Eastern Boundary (similar to 10 degrees W). Drogued Argos buoy and ALACE tracks are superposed on infrared satellite images in the Subtropical Front region. Cold (cyclonic) structures, called 'Storms', and warm (anticyclonic) structures of 100-300 km in size can be found on the south side of the Subtropical Front outcrop, which has a temperature contrast of about 1 degrees C chat can be followed for similar to 2500 km near 35 degrees N. Warmer water adjacent to the outcrop is flowing eastward (Azores Current) but some warm water is returned westward about 300 km to the south (southern Counterflow). Estimates of horizontal diffusion in a Storm (D= 2.2 x 10(2) m(2) s(-1)) and in the Subtropical Front region near 200 m depth (D-x= 1.3 x 10(4) m(2) s(-1), D-y= 2.6 x 10(3) m(2) s(-1)) are made from the Lagrangian tracks. Altimeter and in situ measurements show that Storms track westwards. Storms are separated by about 510 km and move westward at 2.7 km d(-1). Remote sensing reveals that some initial structures start evolving as far east as 23 degrees W but are more organized near 29 degrees W and therefore Sterns are about 1 year old when they reach the MAR (having travelled a distance of 1000 km). Structure and seasonality in SeaWiFS data in the region is examined.

JOURNAL OF THE MARINE BIOLOGICAL ASSOCIATION OF THE UNITED KINGDOM 79: (5) 769-792 OCT 1999

Key Words: North-Atlantic Ocean, Azores Front, Southern Bay, Altimeter, Biscay, Fields, Rings, Ridge, East, Flow

Abstract: The circulation and upwelling processes that control the phytoplankton distribution in the Alboran Sea (western Mediterranean) are examined from a climatological perspective for the first time. To characterize t he annual cycle of the near-surface phytoplankton patterns, we analyze the monthly distributions of pigments from the Coastal Zone Color Scanner (CZCS). Two regimes occur: a fall-to-winter bloom (November-March) and a non-bloom period (May-September). These regimes differentiate the basin from other parts of the western Mediterranean, where a significant spring bloom occurs. The newest ocean color data sets available today from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and the Ocean Color and Temperature Scanner (OCTS) fall within this annual progression. The combined interaction of seasonal stratification, coastal and gyre-induced upwelling, and horizontal advection control the near-surface pigment distribution in Alboran, while light availability does not determine the seasonal cycle of pigments.

GEOPHYSICAL RESEARCH LETTERS 26: (19) 2985-2988 OCT 1 1999

Key Words: Anticyclonic Gyres

Abstract: High-quality ocean color data (chlorophyll) provided by the Sea-viewing Wide Field of view Sensor (SeaWiFS) satellite were analyzed for the first complete year of coverage (October 1997 to September 1998) in the tropical Indo-Pacific basin. This period coincides with the peak of one of the strongest Fl Nino events during December 1997 and the La Nina of 1998 that appeared dramatically in less than a month as a sea surface temperature (SST) change of over 6 degrees C in the central equatorial Pacific during June 1998, The tropical Indian Ocean also underwent a highly anomalous series of events with negative SST anomalies (SSTA) of over 3 degrees C in the eastern equatorial and coastal regions during October-December 1997 and warm SSTA in the west that peaked at over 2 degrees C during February 1998. The ocean color variability is interpreted using other satellite data such as sea level from TOPEX/Poseidon and also in terms of the dynamics and thermodynamics of the region from simulations with an ocean general circulation model, The El Nino-related reductions in equatorial production and the off-equatorial increase in biological activity, and their basin scale evolution is clearly seen for the first time. Persistent northerly wind anomalies resulted in a northward shift of the equatorial divergence and the upwelling Kelvin wave which signalled the end of the 1997-1998 El Nino. The anomalous surface chlorophyll associated with this Kelvin wave was also clearly shifted north of the equator by nearly 300 km and appeared more than a month before the negative sea level anomalies seen by TOPEX/Poseidon. On the equator near 165 degrees E, the disappearance of the barrier layer appeared to coincide with a localized bloom that occurred in response to the easterly wind bursts over the western Pacific that lasted from December 1997 through the boreal summer. The ecosystem response to the cold La Nina conditions is clearly seen as elevated chlorophyll during the boreal summer of 1998 in the equatorial Pacific cold tongue region. In the Indian Ocean, an anomalous phytoplankton bloom was observed by SeaWiFS during October-December 1997 coincident with the anomalous upwelling in the eastern equatorial region and off the coast of Sumatra, A stronger than normal northeast monsoon is seen as higher than climatological values of surface chlorophyll. The open ocean Ekman pumping and the shoaling of the thermocline near 60 degrees E and 10 degrees S and the eastward extension of mixed layer entrainment in the same latitude band is seen as a region of higher biological activity during the boreal summer.

JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 104: (C8) 18351-18366 AUG 15 1999

Key Words: Western Equatorial Pacific, Mixed-Layer Model, Arabian Sea, Indian-Ocean, El-Nino, Surface-Layer, Wind Stress, Phytoplankton, Simulation, Circulation

Abstract: The variability of sea surface chlorophyll concentration in the tropical and subtropical Atlantic during the first year of Sea-viewing Wide Field-of-view Sensor (SeaWiFS) imagery is examined. An Ocean General Circulation Model (OGCM) is used, along with TOPEX/Poseidon dynamic height observations and global gridded wind stress data sets, to explain the physical forcing of surface ocean color signals. Regions of high surface chlorophyll are strongly correlated with mesoscale and large-scale physical processes such as the strong upwelling off the west coast of Africa, the relatively high oceanic production within the Guinea Dome region, and the generation and propagation of large anticyclonic eddies along the coast of South America, north of the equator. The major river outflows (Amazon, Orinoco, and Congo) have strong signatures with plumes of apparently high Chi a in excess of 10 mg m(-3) near their deltas. The fall bloom in the eastern tropical Atlantic observed by the Coastal Zone Color Scanner (CZCS) was absent in 1997, whereas a bloom was observed in this region in July-September 1998, which was not observed by the CZCS, We attribute these apparent anomalies to the projection of the 1997-1998 El Nine event into the tropical Atlantic basin; these signals are correlated with sea surface temperature anomalies known to be associated with ENSO, The SeaWiFS images show that there are seasonal blooms within the hydrographic provinces of the Guinea and Angola domes. These hydrographic provinces are characterized by the dynamic uplift of the thermocline at the North Equatorial Current southern boundary (Guinea Dome) and the Benguela Current eastern boundary (Angola Dome). Within these domes, the Ekman pumping and transport are significant due to the strong trade winds at the surface. The Ekman drift plays a major role in the spreading of surface blooms, The spreading of the oceanic bloom at 12 degrees N, 30 degrees W, the Congo River plume, and the areal extent of the upwelling blooms off the coast of Africa, parallels the strength and extent of the Ekman surface drift. Upwelling, when broadly defined to include large scale vertical excursions of the thermocline, explains virtually all of the surface chlorophyll observations in excess of 0.5 mg m(-3), except in the river plumes.

JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 104: (C8) 18367-18382 AUG 15 1999

Key Words: North-Atlantic, Thermal Domes, Ocean, Sea, Algorithms, Simulation, Model, Cycle

Abstract: We report on the lunar and solar measurements used to determine the changes in the radiometric sensitivity of the Sea-viewing Wide Field-of-view Senses (SeaWiFS). Radiometric sensitivity is defined as the output from the instrument (or from one of the instrument bands) per unit spectral radiance at the instrument's input aperture. Knowledge of the long-term repeatability of the SeaWiFS measurements is crucial to maintaining the quality of the ocean scenes derived from measurements by the instrument. For SeaWiFS bands 1-6 (412-670 nm), the change in radiometric sensitivity is less than 0.2% for the period from November 1997 through November 1998. For band 7 (765 nm), the change is approximately 1.5% and for band 8 (865 nm) approximately SE. The rates of change of bands 7 and 8, which were linear with time for the first eight months of lunar measurements, are now slowing. The scatter in the data points about the trend lines in this analysis is less than 0.3% for all eight SeaWiFS bands. These results are based on monthly measurements of the moon. Daily solar measurements using an onboard diffuser show that the radiometric sensitivities of the SeaWiFS bands have changed smoothly during the time intervals between lunar measurements. Because SeaWiFS measurements have continued past November 1998, the results presented here are considered as a snapshot of the instrument performance as of that date.

APPLIED OPTICS 38: (21) 4649-4664 JUL 20 1999

Key Words: Zone Color Scanner, Nimbus-7 Czcs, Calibration, Radiance, Imagery, Ocean

Abstract: Measurements from the Southern Ocean show that particulate organic carbon (POC) concentration is welt correlated with the optical backscattering by particles suspended in seawater. This relation, in conjunction with retrieval of the backscattering coefficient from remote-sensing reflectance, provides an algorithm for estimating surface POC from Satellite data of ocean color. Satellite imagery from SeaWiFS reveals the seasonal progression of POC, with a zonal band of elevated POC concentrations in December coinciding with the Antarctic Polar Front Zone. At that time, the POC pool within the top 100 meters of the entire Southern Ocean south of 40 degrees S exceeded 0.8 gigatons.

SCIENCE 285: (5425) 239-242 JUL 9 1999

Key Words: Optical-Properties, Light-Scattering, Waters, Phytoplankton, Inherent, Nitrogen, Volume, Color

Abstract: The purpose of the current work was to test the performance of several published CZCS (Coastal Zone Color Scanner) Case 1 algorithms for retrieving pigment concentration and vertical attenuation coefficients in Danish coastal waters. This involves in situ measurements and water samples from the North Sea, the Kattegat, the inner Danish Waters and the Baltic Sea. The entire record of CZCS acquisitions of Danish waters was compared with actual cruise ship data of the Danish National Environmental Research Institute (NERI)-14 days matched exactly but, mainly due to cloud cover, a total of only 38 trustworthy data points were found on seven of these. Vertical attenuation coefficients were estimated from profiles of PAR intensity. Pigment concentrations were determined from spectrophotometric measurements on water samples (chlorophyll-a plus phaeopigment). Correlations between CZCS and in situ estimates were found, but the biases were strong, particularly in the case of pigment concentration. This was as expected because of the extensive amounts of yellow substances present in Danish waters. Therefore, a correction procedure for excluding the yellow substance contribution in pigment concentration retrieval was tested. The results seem promising, but the number of observations is small, and further studies are needed before firm conclusions can be drawn. Nevertheless, it can be stated that trustworthy algorithms for Danish waters for new ocean colour instruments (OCTS, SeaWiFS and MERIS) clearly need to take the absorption by yellow substances into consideration.

INTERNATIONAL JOURNAL OF REMOTE SENSING 20: (7) 1289-1301 MAY 10 1999

Key Words: Remote Measurements, Color

Abstract: SeaWiFS estimates of surface chlorophyll concentrations are reported for the region of the U.S. JGOFS study in the Southern Ocean (similar to 170 degrees W, 60 degrees S). Elevated chlorophyll was observed at the Southern Ocean fronts, near the edge of the seasonal ice sheet, and above the Pacific-Antarctic Ridge. The elevated chlorophyll levels associated with the Pacific-Antarctic Ridge are surprising since even the crest of the ridge is at depths > 2000 m. This elevated phytoplankton biomass is likely the result of mesoscale physical-biological interactions where the Antarctic Circumpolar Current (ACC) encounters the ridge. Four cruises surveyed this region between October 1997 and March 1998, as part of the U.S. JGOFS. Satellite-derived chlorophyll concentrations were compared with in situ extracted chlorophyll measurements from these cruises. There was good agreement (r(2) of 0.72, from a linear regression of shipboard vs, satellite chlorophyll), although SeaWiFS underestimated chlorophyll concentrations relative to the ship data.

GEOPHYSICAL RESEARCH LETTERS 26: (10) 1465-1468 MAY 15 1999

Key Words: Phytoplankton

Abstract: The Agulhas system (Agulhas Current, Retroflection, Agulhas Return Current (ARC)), south of Africa, constitutes a complex energetic system subject to high frequency mesoscale and low frequency variability. Using chlorophyll pigment concentration data collected by the SeaWiFS ocean color sensor and sea surface height satellite data, we demonstrate the utility of wavelet analysis in jointly analyzing ocean color and altimetric signals. Two distinct dynamical scenarios of the Agulhas system (October 1997 and January 1998) yield different dominant wavelengths (620 and 500 km) for the ARC Rossby wave. They are simultaneously retrieved from the chlorophyll and sea level anomaly signals. Longitudinal extension of the power, resulting from the wavelet analysis, also depends on the dynamical regime.

GEOPHYSICAL RESEARCH LETTERS 26: (10) 1469-1472 MAY 15 1999

Key Words: Agulhas Return Current, Region, Retroflection, System

Abstract: The Sea-viewing Wide Field-of-view Sensor (SeaWiFS) was designed to measure ocean colour, the spectral variation of water-leaving radiance that can be related to the concentrations of phytoplankton pigments, coloured dissolved organic material and suspended particulate matter. The Dundee Satellite Receiving Station records and archives l-km imagery covering the European shelf-seas, north-east Atlantic Ocean and Mediterranean Sea, which is subsequently processed in near-real time by Plymouth Marine Laboratory using SeaWiFS Automatic Processing System (SeaAPS). SeaWiFS imagery is combined with contemporary Advanced Very High Resolution Radiometer (AVHRR) sea surface temperature data to provide products, supplied via the World Wide Web, that are used within many areas of oceanographic research.

INTERNATIONAL JOURNAL OF REMOTE SENSING 20: (6) 1051-1056 APR 15 1999

Abstract: The use of CZCS-type band-ratio algorithms to estimate the diffuse attenuation coefficient, percentage light depths, and near-surface optically weighted phytoplankton pigment concentrations from remotely sensed ocean colour data was investigated on two cruises in the Arabian Sea and Gulf of Oman during autumn and winter 1994. The variations of upwelling radiance and downwelling irradiance with depth were measured along with phytoplankton pigment concentrations by HPLC. A spectroradiometer was used on the second cruise to investigate the feasibility of measuring water-leaving radiance from above the sea surface. Retrieval of the diffuse downwelling attenuation coefficient at 490 nm was accurate to within 22% of the actual value across both cruises. There was also a robust relationship between the diffuse attenuation coefficient and the 10, 1 and 0.1% light depths. Above-surface estimates of water-leaving radiance agreed with SeaWiFS-standard estimates to within 10% between 443 and 555 nm. The global 443: 555 band-ratio algorithms of Aiken et al. [NASA Tech. Memo 104566, Vol. 29, SeaWiFS Technical Report Series, 34 pp] estimated near-surface chlorophyll-a and fluorometric pigment concentrations with mean absolute errors of less than 35% of the actual values (which were all less than 2.0 mg m(-3)). The performance of algorithms based on the 490:555 ratio was poorer. The estimates given by the algorithms were generally higher than the measured pigment concentrations and the variance of the accuracy of the estimates was high. There appears to be no significant change in the performance of the algorithms between cruises (approximately 2 1/2 months apart in time). There is no evidence that the Gulf of Oman should be treated as a separate bio-optical province to the Arabian Sea/Omani shelf area for the purpose of the retrieval of near-surface pigment concentrations from ocean colour observations. (C) 1999 Elsevier Science Ltd. All rights reserved.

DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 46: (3-4) 549-569 1999

Key Words: Dissolved Organic-Matter, North-Atlantic, Phytoplankton, Absorption, Coastal

Abstract: Taiwan's first scientific experimental satellite, ROCSAT-1, is scheduled to be launch in January 1999. Kt will carry three scientific payloads. One of them is an instrument named Ocean Color Imager (OCI) to monitor ocean colors, There are two major working groups for the scientific purpose of OCI, the Science Team (ST) and the Science Data Distribution Center (SDDC). The OCI-ST was formed for sensor calibration, atmospheric correction, algorithm development, and data validation. The OCI algorithms developed were tested by Sea-viewing Wide Field-of-view Sensor (SeaWiFS) data, The results show that the relative error of water-leaving radiance from OCI atmospheric correction algorithms is higher than that derived from SeaWiFS algorithms. However, the relative error of chlorophyll a concentration derived from OCI bio-optical algorithm using the water-leaving radiance derived from OCI atmospheric correction algorithms is smaller than that for SeaWiFS products. Data from OCI will be processed and then distributed by the OCI-SDDC. The OCI-SDDC is also a day-to-day operations center. Anyone who is interested in OCI products can request them via the OCI-SDDC web site at http://www.oci.ntou.edu.tw/.

TERRESTRIAL ATMOSPHERIC AND OCEANIC SCIENCES 85-98, Suppl. S MAR 1999

Key Words: Ocean Color Imager, ROCSAT-1, Science Data Distribution Center, Science Team, Ocean Color, Remote Sensing, Algorithm

Abstract: The total radiance observed by satellite-borne ocean color sensors results from several contributions: the atmospheric molecular and aerosol scattering, the sea surface reflectance and the water leaving radiance. In order to apply these ocean color sensor data to access the ocean parameters, atmospheric correction should be undertaken in advance to extract the water leaving radiance that is relevant to the ocean parameters. The aim of this study is to establish one atmospheric correction process for the Ocean Color Imager (OCI) of ROCSAT-1, and some pre-launch simulation results are demonstrated. The simulation shows that the water leaving radiance estimation seems to be reliable by the ocean color radiance algorithm proposed in this paper, because the estimated total pigment concentration seems to be reasonable. Further investigations done in this study using SeaWiFS data reveal that the water leaving radiance is somewhat overestimated in comparison with ship measurements because of the underestimated aerosol scattering. The reason for this underestimation is probably the inconsistent marine aerosol type and size distribution between the real and input atmospheric parameters. The simulated result also shows the sun glint effect is significant and plays the most important role in the radiance contributions of OCI imagery. Consequently, choosing the most suitable acquiring time of OCI in order to avoid the sun glint effect will be very important in future OCI operation scheduling.

TERRESTRIAL ATMOSPHERIC AND OCEANIC SCIENCES 99-114, Suppl. S MAR 1999

Key Words: OCI, Atmospheric Correction, Water Leaving Radiance, Sun Glint, Scanner, Algorithm, Aerosol, Model

Abstract: AVHRR satellite imagery was evaluated as a potential data source for monitoring light attenuation (K-PAR), as a measure of turbidity, in Pamlico Sound estuary, North Carolina. In situ water quality data and reflectance imagery collected on 10 different dates were used to calibrate a general optical equation relating satellite-derived reflectance (R-d), nominally R-(630 nm) to K-PAR. Additional spectral data (e.g., absorption, subsurface reflectance), related reflectance and K-PAR to changes in phytoplankton pigments, organic matter, and suspended sediments. Optically, Pamlico Sound, North Carolina is dominated by scattering from suspended sediments, whereas the tributary rivers are dominated by absorption from both dissolved and particulate organic matter. A general relationship developed between R-d and K-PAR (r(2)=0.72) in Pamlico Sound was found useful in a variety of environmental conditions; however a relationship between R-d and suspended sediment concentration was less robust, and affected by changing sediment characteristics. In the rivers, high and variable absorption in the visible wavelengths precluded development of a relationship between R-d and K-PAR. The relationship developed between R-d and K-PAR in Pamlico Sound is similar to those determined for Delaware Bay and Mobile Bay in previous studies, suggesting possible broader regional application of algorithms for coastal bays and estuaries having similar sediment characteristics, with direct application to SeaWiFS data. Published by Elsevier Science Inc.

REMOTE SENSING OF ENVIRONMENT 68: (1) 41-52 APR 1999

Key Words: Moderately Turbid Estuary, Dissolved Organic-Matter, Neuse River Estuary, Attenuation Coefficient, North-Carolina, Oceanic Waters, Phytoplankton, Absorption, Reflectance, Quality

Abstract: Atmospheric correction in ocean-color remote sensing corrects more than 90% of signals in the visible contributed from the atmosphere measured at satellite altitude. The Sea-viewing Wide Field-of-view Sensor (SeaWiFS) atmospheric correction uses radiances measured at two near-infrared wavelengths centered at 765 and 865 nm to estimate the atmospheric contribution and extrapolate it into the visible range. However, the SeaWiFS 765-nm band, which covers 745-785 nm, completely encompasses the oxygen A-band absorption. The O-2 A-band absorption usually reduces more than 10-15% of the measured radiance at the SeaWiFS 765-nm band. Ding and Gordon [Appl. Opt. 34, 2068-2080 (1995)] proposed a numerical scheme to remove the O-2 A-band absorption effects from the atmospheric correction. This scheme has been implemented in the SeaWiFS ocean-color imagery data-processing system. I present results that demonstrate a method to validate the SeaWiFS 765-nm O-2 A-band absorption correction by analyzing the sensor-measured radiances at 765 and 865 nm taken looking at the clouds over the oceans. SeaWiFS is usually not saturated with cloudy scenes because of its bilinear gain design. Because the optical and radiative properties of water clouds are nearly independent of the wavelengths ranging from 400 to 865 nn, the sensor-measured radiances above the cloud at the two near-infrared wavelengths are comparable. The retrieved cloud optical thicknesses from the SeaWiFS band 7 measurements are compared for cases with and without the O-2 A-band absorption corrections and from the band 8 measurements. The results show that, for air-mass values of 2-5, the current SeaWiFS O-2 A-band absorption correction works reasonably well. The validation method is potentially applicable for in-orbit relative calibration for SeaWiFS and other satellite sensors.

APPLIED OPTICS 38: (6) 937-944 FEB 20 1999

Key Words: Water-Leaving Radiance, Ocean-Color Imagery, Atmospheric Correction

Abstract: A Neural network (NN) algorithm was constructed to estimate oceanic chlorophyll concentrations from Sea-viewing Wide Field-of-view Sensor (SeaWiFS) data. The algorithm was trained and tested using sample data compiled at the SeaWiFS Bio-optical Algorithm Mini-workshop. A NN using the five visible SeaWiFS bands as inputs with ten nodes in a single hidden layer estimates chlorophyll concentrations efficiently and accurately, modelling the nonlinear transfer function between surface chlorophyll concentrations and remotely sensed reflectance data more accurately than traditional regression methods.

INTERNATIONAL JOURNAL OF REMOTE SENSING 20: (1) 189-194 JAN 10 1999

Abstract: With the success of launch and initial data processing of Sea-viewing Wide Field-of-view Sensor (SeaWiFS), there is a great interest in ocean color community to intercompare ocean color data between different ocean color sensors. it is well known that the atmospheric correction, which removes about 90% of sensor-measured signals contributed from atmosphere in the visible, is the key procedure in ocean color imagery data processing. Therefore, it is useful to evaluate the SeaWiFS atmospheric correction algorithm applying to various ocean color sensors. The SeaWiFS atmospheric correction agorithm uses lookup tables which were generated with over similar to 25,000 radiative transfer model runs for different aerosol optical and microphysical properties, solar and viewing geometries, and, in particular, at the eight SeaWiFS spectral bands. Since different ocean color sensors usually have different band spectral characterization, it is rather difficult to apply the SeaWiFS atmospheric correction algorithm to other sensors if one needs to regenerate lookup tables at spectral bands different from SeaWiFS. In this article, we evaluate the accuracy of the SeaWiFS atmospheric correction algorithm for various ocean color sensors using the current SeaWiFS lookup tables. The focus in on the following satellite ocean color sensors: the Modular Optoelectronic Scanner (MOS), the Ocean Color and Temperatures Sensor (OCTS), and the Polarization and Directionality of the Earth's Reflectances (POLDER). These sensors have slightly different spectral bands compared with the SeaWiFS. It was found that, with an appropriate calculation of the Rayleigh scattering contributions at each sensor's spectral band and a simple modification in computing the diffuse transmittance of the ocean-atmosphere system, the SeaWiFS atmospheric correction applied to other sensors is as accurate as for SeaWiFS for the solar zenith angles theta(0) less than or equal to 60 degrees.
© Elsevier Science Inc., 1999.

REMOTE SENSING OF ENVIRONMENT 67: (3) 348-359 MAR 1999

Key Words: Multiangle Imaging Spectroradiometer, Water-Leaving Radiance, Ocean-Color Sensors, Optical-Thickness, Instrument, Imagery, System, Earth

Abstract: Funding from NASA's Ocean Biogeochemistry Program and the Goddard Space Flight Center SeaWiFS Project was used to implement an ocean optics program as part of the routine cruises of the California Cooperative Oceanic Fisheries Investigations (CalCOFI). Since August 1993, data from more than 300 bio-optical stations have been acquired, merged with complementary data, and made available for developing remote sensing algorithms. The profiling instrument consisted of a Biospherical Instruments, Inc. MER-2040/2041 radiometer integrated with CTD probes, a transmissometer, and a fluorometer. A detailed calibration time series of the radiance and irradiance sensors has been maintained to ensure maximum accuracy. The data set has been used to develop empirical algorithms for Sea WiFS standard products including chlorophyll a (chl a), "CZCS pigments," and diffuse attenuation coefficient K-d(490). Algorithms using cubic regressions of remote sensing reflectance (R-rs) ratios provided the best estimation of chi a and pigments over the full range of chl a (0.05-22.3 mg m(-3)). Multiple linear regressions of multiple-band ratios proved to be less robust. Relationships between spectral K and chi a suggest that previous K algorithms may have errors due to estimates of pure-water absorption.

CALIFORNIA COOPERATIVE OCEANIC FISHERIES INVESTIGATIONS REPORTS 39: 133-147 OCT 1998

Key Words: Natural-Waters, Ocean Color, Absorption, Phytoplankton, Chlorophyll, Variability, Spectra, Matter, nm

Abstract: The international community, recognizing the importance of global ocean color observations in the global carbon cycle, has proposed or flown six global ocean color missions over the next decade: the Ocean Color and Temperature Sensor (OCTS), Sea-viewing Wide Field-of-view Sensor (SeaWiFS), Moderate Resolution Imaging Spectrometer-AM (MODIS-AM), Medium Resolution Imaging Spectrometer (MERIS), Global Imager (GLI), and MODIS-PM. Each of these missions contains the spectral band complement considered necessary to derive oceanic pigment concentrations (i.e., phytoplankton abundance). This paper assesses whether assembling and merging data from these missions can improve ocean coverage, since clouds and sun glint prevent any single satellite from observing more than about 15% of the ocean surface in a single day, and whether new information about diel cycles of phytoplankton abundance is possible. Extensive numerical analysis, given the orbit and sensor characteristics of each mission, showed that merging data from three satellites can produce better ocean coverage in less time. Data from three satellites can improve coverage by 58% for a single day, including the obscuring effects of clouds and sun glint. Thus, observation of approximately 25% of the ocean can be provided, instead of only about 15-16% from a single satellite. After four days, approximately 62% of the ocean surface was observed, an increase from 43% observed by a single satellite, The addition of more satellites produced diminishing returns. Since the proposed missions have different orbits, they view the same location of the ocean at different times of day, This leads to the possibility of using data from the set of six missions to help understand diel phytoplankton dynamics. The missions produced colocated observations as much as 16 h apart in the high latitudes. However, given the distributions of land masses and ice cover, only a maximum of 14-h spacing could actually be achieved, and this only at high latitudes at the solstices, However, large differences of 4-10 h are readily available at other latitudes and in frequencies numbering in the tens of thousands at 20 degrees latitude bands. This suggests that combinations of these missions can support new observations of the higher frequency dynamics of phytoplankton populations in the oceans and help determine how well observations taken at a single time represent the daily abundance.

IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING 36: (5) 1620-1627, Part 1 SEP 1998

KeyWords: Temperature, Sensors, Sea

No Abstract Available

SEA TECHNOLOGY 39: (9) 10-16 SEP 1998

Key Words: Coastal

Abstract: A large data set containing coincident in situ chlorophyll and remote sensing reflectance measurements was used to evaluate the accuracy, precision, and suitability of a wide variety of ocean color chlorophyll algorithms for use by SeaWiFS (Sea-viewing Wide Field-of-view Sensor). The radiance-chlorophyll data were assembled from various sources during the SeaWiFS Bio-optical Algorithm Mini-Workshop (SeaBAM) and is composed of 919 stations encompassing chlorophyll concentrations between 0.019 and 32.79 mu g L-1. Most of the observations are from Case I nonpolar waters, and similar to 20 observations are from more turbid coastal waters. A variety of statistical and graphical criteria were used to evaluate the performances of 2 semianalytic and 15 empirical chlorophyll/pigment algorithms subjected to the SeaBAM data. The empirical algorithms generally performed better than the semianalytic. Cubic polynomial formulations were generally superior to other kinds of equations. Empirical algorithms with increasing complexity (number of coefficients and wavebands), were calibrated to the SeaBAM data, and evaluated to illustrate the relative merits of different formulations. The ocean chlorophyll 2 algorithm (OC2), a modified cubic polynomial (MCP) function which uses Rrs490/Rrs555, well simulates the sigmoidal pattern evident between log-transformed radiance ratios and chlorophyll, and has been chosen as the at-launch SeaWiFS operational chlorophyll a algorithm. Improved performance was obtained using the ocean chlorophyll 4 algorithm (OC4), a four-band (443, 490, 510, 555 nm), maximum band ratio formulation. This maximum band ratio (MBR) is a new approach in empirical ocean color algorithms and has the potential advantage of maintaining the highest possible satellite sensor signal:noise ratio over a 3-orders-of-magnitude range in chlorophyll concentration.

JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 103: (C11) 24937-24953 OCT 15 1998

Key Words: Remote-Sensing Reflectance, Cross-Spectrum Analysis, Optical-Properties, Coastal Waters, Sargasso Sea, Phytoplankton Absorption, Coccolithophore Blooms, Primary Productivity, Biogenous Matter, Light-Absorption

Abstract: The aim of this note is to test an empirical algorithm using spectral curvature theory at selected SeaWiFS hyerspectral bands, in order to estimate the chlorophyll pigment concentrations in the coastal waters of Bale des Chaleurs (Gulf of St. Lawrence). Simulated SeaWiFS algorithms require the measurement of reflectances with a high sensitive spectroradiometer as well as the responsitivity of SeaWiFS sensor at each band. Volume reflectances were taken using a hand held spectroradiometer simultaneously to measurements of in situ chlorophyll pigment concentrations. An empirical algorithm of the form: log (chlorophyll pigments)=0.92-0.46 Delta(2) log R-0sea(555) yields an estimate of chlorophyll pigment concentrations within a mean delta C/C of 23%.

INTERNATIONAL JOURNAL OF REMOTE SENSING 19: (11) 2161-2169 JUL 20 1998

Key Words: Coastal Waters, Phytoplankton, Pigments, Ocean

Abstract: One of the goals of calibration and validation programs supporting ocean color satellites is to produce water-leaving radiances with an uncertainty of 5% in clear-water regions. This objective requires field instruments with a calibration and measurement capability that is on the order of 1%. The Sea-viewing Wide Field-of-view Sensor (SeaWiFS) Project, in collaboration with the National Institute of Standards and Technology, has developed a portable illumination source with three temperature-stabilized internal monitors designed to provide a stable light held for checking the optical stability of radiometers used to measure the in situ optical properties of seawater. This device is called the SeaWiFS Quality Monitor (SQM). A recent field evaluation during an extensive research cruise indicates the SQM has the following capabilities: (a) the SQM can be used to track the stability of field radiometers at less than the 1% level in terms of the radiometric response of the instruments-on average 0.30% (+/-0.15%) for radiance sensors and 0.58% (+/-0.20%) for irradiance sensors: (b) the SQM light field is sufficiently stable to allow for a sensitive measure and, thus, modeling of changes in the radiometric detectors; (cf based on the radiometers used during the field evaluation, daily SQM measurements are needed to resolve the temporal changes in the response of the sensors; and (d) SQM performance, in terms of the generated light field and the SQM internal monitors, is very stable and decayed only by approximately 0.60% during the course of the 36-day deployment with most of the decay attributed to a change in the operating voltage of one of the lamps.

JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 15: (4) 995-1007 AUG 1998

Key Words: Ocean

Abstract: A portable and stable source of radiant flux, the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) Quality Monitor (SQM), was developed as a field instrument for use in experiments away from the calibration laboratory such as those encountered during oceanographic cruises. The SQM monitors the radiometric stability of radiance and irradiance sensors during these field experiments; a companion paper gives results acquired during the third Atlantic Meridional Transect cruise. In conjunction with laboratory calibration sources, the SQM can be used to transfer the calibration to the field experiment. Two independent lamp assemblies generate three flux levels, and me lamps are operated at constant current using active control. The exit aperture of the SQM is large and homogeneous in radiance. The SQM was designed to approximate a Lambertian radiator. An internal heater provides operational stability and decreased warmup intervals, which minimizes lamp hours.

Temperature-controlled silicon photodiodes with colored-glass filters monitor the stability of the SQM, which is better than 1%. These independent monitors, which are integrated with the SQM, provide information on the Aux from the SQM and can be used to normalize the output from the field radiometers during the experiment. Three reference devices, or fiducials, which are designed to mimic the optical surfaces of the held radiometers but are not functioning detector units, are used in place of the field radiometers to produce baseline monitor signals. The front surface of the fiducial is protected when not in use and kept clean during the field experiment. The monitor signals acquired using the fiducials provide additional information on the radiometric stability of the SQM. A kinematically designed mounting ring is used on both the field radiometers and the fiducials to ensure the devices being tested view the same part of the exit aperture each time they are used.

JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 15: (4) 1008-1022 AUG 1998

Key Words: Standard Lamps

Abstract: In 1998, NASA launches EOS-AM1, the first of a series of the Earth Observing System (EOS) satellites. EOS will monitor the evolution of the state of the earth for 18 years, starting with the morning observations of EOS-AM1 (10:30 a.m. equatorial crossing time). An integrated view of the earth, as planned by EOS, is needed to study the interchange of energy, moisture, and carbon between the lands, oceans, and atmosphere. The launch of EOS-AM1 and other international satellites marks a new phase of climate and global change research. Both natural and anthropogenic climate change have been studied for more than a century. It is now recognized that processes that vary rapidly in time and space-e.g, aerosol, clouds, land use, and exchanges of energy and moisture-must be considered to adequately explain the temperature record and predict future climate change. Frequent measurements with adequate resolution, as only possible from spacecraft, are key tools in such an effort. The versatile and highly accurate EOS-AM1 data, together with previous satellite records, as well as data from the Advanced Earth Observing System (ADEOS) (I and II), Tropical Rainfall Measuring Mission (TRMM), Sea-viewing Wide Field-of-view Sensor (SeaWiFS), Along Track Scanning Radiometer (ATSR), Medium Resolution Imaging Spectrometer (MERIS), Environmental Satellite (ENVISAT), EOS-PM1, Land Remote-Sensing Satellite (Landsat), and ground-based networks is expected to revolutionize the way scientists look at climate change. This article introduces the EOS-AM1 mission and the special issue devoted to it. Following a brief historical perspective for an insight into the purpose and objectives of the mission, we shall summarize the characteristics of the five instruments onboard EOS-AM1. Specifically, we concentrate on the innovative elements of these five instruments and provide examples of the science issues that require this type of data. These examples show the importance of collecting data simultaneously from each of the five EOS-AM1 sensors for studying rapidly varying processes and parameters.

IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING 36: (4) 1045-1055 JUL 1998

Key Words: Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Aerosol, Anthropogenic Forcing, Atmospheric Chemistry, Biomass Burning, Carbon Cycle, Carbon Dioxide, Climate, Climate Change, Clouds, Clouds and Earth's Radiant Energy System (CERES), Earth Observing System (EOS)-AM1, Earth Science, Global Change, Global Warming, Greenhouse Gas, Land Use, Measurements Of Pollution In The Troposphere (MOPITT), Moderate Resolution Imaging Spectroradiometer (MODIS), Multi-angle Imaging SpectroRadiometer (MISR), Phytoplankton, Predictive Computer Models, Radiation Budget, Remote Sensing, Sea Surface Temperature, Troposphere, Vegetation, Atmospheric CO₂, Export Production, Iron, Rise

Abstract: Large improvements in coverage frequency (daily to four-day) can be expected by combining ocean color data from the Sea-Viewing Wide Field-Of-View Sensor (Sea WiFS) and Moderate Resolution Imaging Spectrometer (MODIS) missions. Results indicated 40-47% increases in global coverage over SeaWifS alone in one day and >100% in low latitudes. The missions are highly complementary for observation of short-term processes.

IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING 36: (4) 1350-1353 JUL 1998

Key Words: Biology, Remote Sensing, Sea Surface

Abstract: Optical data were collected during two U.S. JGOFS EqPac Time Series cruises aboard the U.S. Research Vessel Thomas G. Thompson, at a station at 140 degrees W on the equator, during the time of both the first equinox and the second equinox of 1992. This data set represents the range of conditions expected in this region, and was used to compare the SeaWiFS chlorophyll a algorithm with the CZCS pigment algorithm, as well as test the validity of using ocean color remote sensing to track the biological response to physical phenomena such as Kelvin Waves and Tropical Instability Waves (TIW). Time Series I (23 March to 9 April) took place during the maximum expression of the 1991-92 El Nino event, and coincided with the peak of a passing Kelvin wave. Time Series II (2-21 October) occurred during La Nina conditions and encompassed the passage of a TIW. The SeaWiFS pigment compared favorably with the earlier CZCS pigment algorithm and indicate that the SeaWiFS algorithm is capable of determining both quantitative and qualitative changes in surface chlorophyll a from remotely sensed optical data in high nutrient, low chlorophyll regions such as the Equatorial Pacific. Our results show that, although Kelvin waves can not be currently tracked using ocean color sensors alone, when a Kelvin wave is detected by other methods, satellite ocean color data can be used to characterize the biological response to the Kelvin wave. However, since TIWs have a much shorter period and can enhance near-surface phytoplankton growth rates quickly, they can be tracked using remotely sensed ocean color data using either the CZCS pigment or the SeaWiFS chlorophyll algorithm.
© 1998 Elsevier Science Ltd. All rights reserved.

DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY 44: (9-10) 1907-1925 1997

Key Words: Reflectance Model, Ocean-Color, Waters

Abstract: The development of water quality retrieval algorithms is discussed in terms of causal dependence of the upwelling spectral radiance upon the water composition. Unlike clear marine/oceanic waters, for which linear regression retrieval relationships are valid, inland and coastal zone water masses with a high degree of optical complexity necessitate the development of more subtle retrieval approaches. At the basis of such approaches are models considering the conjoint optical impact of several co-existing aquatic components on the water leaving radiance spectral distribution. Such a model for Lake Ladoga is described. Monte Carlo simulations have been performed to analyse the spectral and angular variations of the upwelling radiance scattered by the water column into the atmosphere. Optimal conditions for conducting water quality remote sensing in case of natural waters of various optical complexity are explored and relevant recommendations are formulated.

INTERNATIONAL JOURNAL OF REMOTE SENSING 19: (5) 957-979 MAR 20 1998

Key Words: Natural-Waters, Chlorophyll, Retrieval, Ontario, Seawifs, Matter, Lakes, Color, Ocean

Abstract: As a part of the pre-flight calibration and validation activities for the Ocean Color and Temperature Scanner (OCTS) and the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) ocean color satellite instruments, a radiometric measurement comparison was held in February 1995 at the NEC Corporation in Yokohama, Japan. Researchers from the National Institute of Standards and Technology (NIST), the National Aeronautics and Space Administration/Goddard Space Right Center (NASA/GSFC), the University of Arizona Optical Sciences Center (UA), and the National Research Laboratory of Metrology (NRLM) in Tsukuba, Japan used their portable radiometers to measure the spec tral radiance of the OCTS visible and near-infrared integrating sphere at four radiance levels. These four levels corresponded to the configuration of the OCTS integrating sphere when the calibration coefficients for five of the eight spectral channels, or bands, of the OCTS instrument were determined. The measurements of the four radiometers differed by -2.7 % to 3.9 % when compared to the NEC calibration of the sphere and the overall agreement was within the combined measurement uncertainties. A comparison of the measurements from the participating radiometers also resulted in agreement within the combined measurement uncertainties. These results are encouraging and demonstrate the utility of comparisons using laboratory calibration integrating sphere sources. Other comparisons will focus on instruments that are scheduled for spacecraft in the NASA study of climate change, the Earth Observing System (EOS).

JOURNAL OF RESEARCH OF THE NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY 102: (6) 627-646 NOV-DEC 1997

Key Words: Calibration, EOS, Integrating Sphere, Measurement Comparison, OCTS, Ocean Color, SeaWiFS, Spectral Radiometry, Remote Sensing, Transfer Radiometers, Calibration, Instrument

Abstract: In algorithms for the atmospheric correction of visible and near-IR satellite observations of the Earth's surface, it is generally assumed that the spectral variation of aerosol optical depth is characterized by an Angstrom power law or similar dependence. In an iterative fitting algorithm for atmospheric correction of ocean color imagery over case 2 waters, this assumption leads to an inability to retrieve the aerosol type and to the attribution to aerosol spectral variations of spectral effects actually caused by the water contents. An improvement to this algorithm is described in which the spectral variation of optical depth is calculated as a function of aerosol type and relative humidity, and an attempt is made to retrieve the relative humidity in addition to aerosol type. The aerosol is treated as a mixture of aerosol components (e.g., soot), rather than of aerosol types (e.g., urban). We demonstrate the improvement over the previous method by using simulated case 1 and case 2 sea-viewing wide field-of-view sensor data, although the retrieval of relative humidity was not successful.
© 1997 Optical Society of America.

APPLIED OPTICS 36: (36) 9448-9455 DEC 20 1997

Key Words: Ocean Color, SeaWIFS, Optical Properties, Multiple Scattering, Error Minimization, Humidity, Ocean Color, Model, Radiance, Aerosol

No Abstract Available

LASER FOCUS WORLD 33: (11) 30-31 NOV 1997

No Abstract Available

BULLETIN OF THE AMERICAN METEOROLOGICAL SOCIETY 78: (11) 2678-2679 NOV 1997

Abstract: An automated method has been developed for performing navigation assessment on satellite-based Earth sensor data. The method utilizes islands as targets which can be readily located in the sensor data and identified with reference locations. The essential elements are an algorithm for classifying the sensor data according to source, a reference catalogue of island locations, and a robust pattern-matching algorithm for island identification. The algorithms were developed and tested for the Sea-viewing Wide Field-of-view Sensor (SeaWiFS), an ocean colour sensor. This method will allow navigation error statistics to be automatically generated for large numbers of points, supporting analysis over large spatial and temporal ranges.

INTERNATIONAL JOURNAL OF REMOTE SENSING 18: (16) 3311-3336 NOV 10 1997

Key Words: AVHRR Image Navigation

Abstract: Sensors that can be used for the observation of ocean color in NASA's Earth Observing System era (SeaWiFS, MODIS, and MISR) have been designed with 2-4 times the radiometric sensitivity of the proof-of-concept ocean color instrument CZCS (coastal zone color scanner). To realize an improvement in the retrieval of biologically important ocean parameters, e.g., the concentration of the photosynthetic pigment chlorophyll a, from this increased sensitivity, significantly better atmospheric correction than was applied to CZCS is required. Atmospheric correction improvement necessitates the inclusion of the effects of multiple scattering, which are strongly dependent on the aerosol size distribution, concentration, and absorption properties. We review the basic concepts of atmospheric correction over the oceans and provide the details of the algorithms currently being developed for SeaWiFS, MODIS, and MISR. An alternate correction algorithm that could be of significant value in the coastal zone is described for MISR. Related issues such as the influence of aerosol vertical structure in the troposphere, polarization of the light field, sea surface roughness, and oceanic whitecaps on the sea surface are evaluated and plans for their inclusion in the algorithm are described. Unresolved issues, such as the presence of stratospheric aerosol, the appropriateness of the aerosol models used in the assessment of multiple scattering, and the identification of, and difficulties associated with the correction for, the presence of absorbing aerosols, e.g., urban pollution or mineral dust, are identified, and suggestions are provided for their resolution.

JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES 102: (D14) 17081-17106 JUL 27 1997

Key Words: Multiangle Imaging Spectroradiometer, Surface-Roughness Considerations, Aerosol Optical-Thickness, Water-Leaving Radiance, Phytoplankton Pigments, Correction Algorithm, Diffuse-Reflectance, Remote Sensors, North-Atlantic, Scattering

Abstract: High resolution aircraft remote sensing imagery and in situ optical data were coupled to characterize the spatial and temporal variability of the inherent optical properties in the near-surf zone off Fort Walton Beach, Florida in August 1994. Upwelling radiance measurements at SeaWiFS wavelengths were collected over a uniform, highly reflective white sand bottom at a ground resolution of 2.5 m using the CASI sensor (Compact Airborne Spectral Imager). Following atmospheric correction, the total remote sensing reflectance signal was partitioned into bottom and water volume reflectance components, using measurements of bottom albedo, water depth, and the diffuse attenuation coefficient at the time of the over-flight. The water components were entered in the Sea-WiFS biooptical model to derive spectral absorption and scattering coefficients. After applying minor algorithm and coefficient adjustments, model results compared favorably with in situ measurements. The biooptical model was subsequently applied to the aircraft imagery to describe the spatial distribution of absorption and scattering. Elevated absorption and particle scattering were observed over the sand bar and shoreward (alpha 555=0.19 m(-1), b555=0.7 m(-1)). The temporal variability of the inherent optical properties over a 1-week period was similar to the spatial variability along a 500-m offshore transect.
Published by Elsevier Science Inc.

REMOTE SENSING OF ENVIRONMENT 61: (2) 290-301 AUG 1997

Key Words: Ocean Color, AVIRIS, Reflectance, Waters, Model, Phytoplankton, Depth, Bay, Sea

Abstract: The backscatter part of the aerosol phase function P-A(chi), where chi is the scattering angle, is difficult to measure from the ground. Experimental data for chi > 120 degrees are not reported in the literature. Customarily, P-A(chi) is calculated from Mie theory using an aerosol size distribution either prescribed or estimated by inversion of spectral or almucantar/aureole measurements. These results clearly require validation using direct measurements. In this paper, an empirical phase function of atmospheric aerosol over the ocean is estimated in backscatter (chi > 130 degrees) from coincident measurements of upward radiance in channel 1 (0.63 mu m) of the Advanced Very High Resolution Radiometer (AVHRR) on board National Oceanic and Atmospheric Administration satellites and sun-photometer aerosol optical thickness, delta(SP)(A). This study uses 31 sun-photometer measurements, collected during two oceanic cruises over the North Atlantic in 1989 and 1991. The accuracies of both satellite radiances and sun-photometer delta(SP)(A) are well documented. The Linearized form of the single-scattering approximation for the radiative transfer equation is used, with some adjustments to account approximately for multiple scattering effects, The newly estimated empirical phase function shows variability from one point to another, but on the average, is close to that expected for maritime aerosols as found in the literature. The results of the present study may be used to constrain the range of variability of the aerosol phase function in real marine atmospheres, which is important for aerosol retrieval from historical Coastal Zone Color Scanner (CZCS), present (AVHRR), and future satellite sensors Moderate-Resolution Imaging Spectroradiometer (MODIS), Multiangle Imaging Spectroradiometer (MISR), and Sea-Viewing-Wide-Field-of-View-Sensor (SeaWiFS).

JOURNAL OF APPLIED METEOROLOGY 36: (6) 688-694 JUN 1997

Key Words: Optical-Properties, Atmospheric Correction, Cloud, Color, Algorithm, Thickness, Oceans, AVHRR

Abstract: Advantage is taken of a unique spectral feature of soil biogenic crust containing cyanobacteria. It has been shown that the special phycobilin pigment in cyanobacteria contributes in producing a relatively higher reflectance in the blue spectral region than the same type of substrate without the biogenic crust. A spectral crust index (CI) has been developed, based on the normalized difference between the RED and the BLUE spectral values: CI = 1 - (RED - BLUE)/(RED + BLUE). Applying the index to a sand dune environment, it has been shown that the CI can be used to detect and to map, from remote sensing imagery, different lithological morphological units, such as, active sands, crusted interdune areas and playas, which are expressed in the topography. As a mapping tool the CI image is much more sensitive to the ground features than the original images. The absence, existence, and distribution of soil crust are an important information for desertification and climate change studies. They are also highly valuable information for developing agricultural regions and/or infrastructures in arid environments since soil crusts contribute to soil stability, soil build-up, soil fertility, and to the soil water regime. The application of the proposed CI can be performed with imagery acquired by any sensor which contains the blue band. Currently, the most common data sources are colour aerial photographs and Landsat TM images as demonstrated in this paper. However, CI should be applicable to other sensors such as the SPOT-VEGETATION, MOMS-2P, SeaWiFS and MODIS which will be available in the coming years.

INTERNATIONAL JOURNAL OF REMOTE SENSING 18: (6) 1207-1220 APR 1997

Key Words: Western Negev Desert, Soil Crusts, Reflectance, Lichens, Israel

Abstract: A realistic simulated data set is essential for mission readiness preparations and can potentially assist in all phases of ground support for a future mission. Such a data set was created for the Sea-viewing Wide Field-of-view Sensor (SeaWiFS), a global ocean color mission due for launch in 1997. This data set incorporates a representation of virtually every known aspect of the flight mission. Thus, it provides a high fidelity data set for testing most phases of the ground system, including data processing, data transfers, calibration and validation, quality control, and mission operations. The data set is constructed for a seven-day period, March 25-31, 1994. Specific features of the data set: it includes Global Area Coverage (GAC), recorded Local Area Coverage (LAC), and real-time High Resolution Picture Transmission (HRPT) data for the seven-day period; it includes a realistic orbit which is propagated using a Brouwer-Lyddane model with drag; the data correspond to a command schedule based on the orbit for this seven-day period; it includes total (at satellite) radiances for ocean, land, clouds, and ice; it utilizes a high-resolution land/sea mask; it includes actual SeaWiFS spectral responses; it includes the actual sensor saturation responses; it is formatted according to current onboard data structures; and it includes corresponding telemetry (instrument and spacecraft) data. The methods are described and some examples of the output are given.

IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING 35: (2) 421-435 MAR 1997

Key Words: Coastal Zone Color Scanner, Ocean Color, Model, Irradiance, Radiance, Atmospheres, Chlorophyll, Algorithm, Sensors

Abstract: Two drifting buoys equipped with downward looking 4-channel colour sensors were deployed south-west of Gran Canaria island in the vicinity of a cyclonic eddy. Diffuse upwelling irradiance was measured in four channels (corresponding to some of the SeaWIFS channels) centred on wavelengths 440, 490, 570 and 670 nm. Chlorophyll concentrations were obtained at the start and end of each buoy deployment from profiles of fluorescence calibrated against extracted chlorophyll samples. A weighted chlorophyll concentration was calculated which corresponded to the depth detected by the colour sensor. The ratio of blue (440 nm) to green (570 nm) wavelength diffuse upwelling irradiance was found to vary in an 'n' shape throughout the day, and the size of the 'n' varied between days and buoy deployments. Possible causes for the observed variations and the problems encountered in calibrating the ratio of blue to green light with chlorophyll concentration are discussed, The surface reflectance ratio of blue to green irradiance was consistent with results in the literature for oceanic waters, with very low near-surface chlorophyll concentrations.
© Copyright 1996 Elsevier Science Ltd.

OPTICS AND LASER TECHNOLOGY 29: (1) 3-8 FEB 1997

Key Words: Upwelling Irradiance, Chlorophyll, Drifting Buoy, Variability

Abstract: A recent comment from Gordon and Evans took issue with two aspects of the analysis of Coastal Zone Color Scanner (CZCS) pigment extraction algorithms. This reply refuted the arguments of Gordon and Evans. The multiple Rayleigh scattering algorithm does not always make physical sense, nor has the physical validity of Angstrom's coefficient been established as a means of parameterizing the aerosol scale factor. We also disagreed with the position put forward by Gordon and Evans that the artifacts in the CZCS data will disappear in the next generation sensor (SeaWiFS) because the problem of quantifying the aerosol contribution from these satellite measurements has not yet been solved to sufficient accuracy. Finally, these factors, coupled with electronic overshoot and the decay of the CZCS sensor's sensitivity over time, make it unlikely that the quality of derived pigment values will be significantly improved by reprocessing the CZCS archive yet one more time as suggested by Gordon and Evans.

INTERNATIONAL JOURNAL OF REMOTE SENSING 17: (17) 3501-3510 NOV 20 1996<

Key Words: Radiometric Sensitivity, NIMBUS-7 CZCS

Abstract: Most animals use a ''green'' spectral range to remotely sense the presence and vitality of vegetation. While humans possess the same ability in their eyes, man-made space-borne sensors that sense evolution of global vegetation, have so far used a combination of the red and near infrared channels instead. In this article we challenge this approach, using measurements of reflectance spectra from 400 nm to 750 nm with spectral resolution of 2 nm, with simultaneous determination of pigment concentrations of mature and autumn senescing leaves. We show that, for a wide range of leaf greenness, the maximum sensitivity of reflectance coincides with the red absorption maximum of chlorophyll-a (Chl-a) at 670 nm. However for yellow-green to green leaves (with Chl-a more than 3-5 mu g/cm(2)), the reflectance near 670 nm is not sensitive to chlorophyll concentration because of saturation of the relationship of absorptions versus chlorophyll concentration. Maximum sensitivity of Chl-a concentration for a wide range of its variation (0.3-45 mu g/cm(2)) was found, not surprisingly so, around the green band from 520 nm to 630 nm and also near 700 nm. We found that the inverse of the reflectance in the green band was proportional to Chl-a concentration with correlation r(2) > 0.95. This band will be present on several future satellite sensors with a global view of vegetation (SeaWiFS to be launched in. 1996, Polder on ADEOS-1 also in 1996, and MODIS on EOS in 1998 and 2000). New indexes that use the green channel and are resistant to atmospheric effects are developed. A green NDVI = (rho(nir) - rho(green)/(rho(nir) + rho(green) was tested for a range of Chl-a from 0.3 mu g/cm(2) to 45 mu g/cm(2), and found to have an error in the chlorophyll a derivation at leaf level of less than 3 mu g/cm(2). The new index has wider dynamic range than the NDVI and is, on average, at least five times more sensitive to Chl-a concentration. A green atmospherically resistant vegetation index (GARI), tailored on the concept of ARVI (Kaufman and Tanre, 1992), is developed and is expected to be as resistant to atmospheric effects as ARVI but more sensitive to a wide range of Chl-a concentrations. While NDVI and ARVI are sensitive to vegetation fraction and to rate of absorption of photosynthetic solar radiation, a green vegetation index like GARI should be added to sense the concentration of chlorophyll, to measure the rate of photosynthesis and to monitor plant stress.
© Elsevier Science Inc., 1996.

REMOTE SENSING OF ENVIRONMENT 58: (3) 289-298 DEC 1996

Key Words: Acer-Platanoides L, Red Edge, Spectral Reflectance, Canopy Reflectance, Leaf Reflectance, Plant Stress, Maple Leaves, Chlorophyll, Autumn, Index

Abstract: A modular atmospheric correction algorithm is proposed that uses atmospheric and water contents models to predict the visible and near-infrared reflectances observed by a satellite over water. These predicted values are compared with the satellite reflectances at each pixel, and the model parameters changed iteratively with an error minimization algorithm. The default atmospheric model uses single-scattering theory with a correction for multiple scattering based on lookup tables. With this model we used parameters of the proportions of three tropospheric aerosol types. For the default water content model we need the parameters of the concentrations of chlorophyll, inorganic sediment, and gelbstoff. The diffuse attenuation and backscatter coefficients attributed to these constituents are calculated and used to derive the water-leaving reflectance. Products include water-leaving reflectance, concentrations of water constituents, and aerosol optical depth and type. We demonstrate the application of the method to sea-viewing wide field-of-view sensor by using model data.
© 1996 Optical Society of America

APPLIED OPTICS 35: (27) 5443-5451 SEP 20 1996

Key Words: Ocean Color, SeaWiFS, Optical Properties, Multiple Scattering, Error Minimization, Suspended Sediment Concentration, Ocean-Color, Phytoplankton Pigments, Optical Classification, Natural-Waters, Coastal Waters, Model, Radiance, Chlorophyll, Absorption

Abstract: The Ambrose Light Tower was selected as a technology development site for the National Aeronautics and Space Administration (NASA) Sea-viewing Wide Field-of-view Sensor (Sea-WiFS) program for ocean color. Optical sensors and other supporting oceanographic instrumentation will be mounted on the tower leg to develop an operational capability for validation, of SeaWiFS data for coastal oceans. The Ambrose Tower, an established weather station, is part of the National Data Buoy Center's (NDBC) Coastal-Marine Automated Network (C-MAN). Simultaneous sampling of meteorological data and in-water optical observations will provide an important component to understanding ocean physics as it relates to variability in productivity.

MARINE TECHNOLOGY SOCIETY JOURNAL 30: (2) 33-38 SUM 1996

Key Words: Bight

Abstract: We examine ways of addressing coastal environmental quality concerns through the use of modeling, measurements, and in the future, satellite remote sensing. In a summary of historical trace-metal concentrations in the waters of Narragansett Bay, we partitioned the estuary into sectors that reflect the morphology of the Bay and the transition between freshwater inputs and offshore coastal waters. We constructed a 24-box two-layer model of the Bay. A convenient summary of the chemical variations in the Bay was provided by a schematic diagram which for a constituent such as copper or other metals displays the average concentration, the range, the standard deviation, and the number of observations in our database for each sector. This diagram shows the spatial gradients through the Bay and the variability within a sector. Using a simple two-layer box model with seven transport terms we computed the physical exchanges between boxes using freshwater input and salinity data The box model approach was applied in greater detail to the upper portion of Narragansett Bay to provide transport terms for use in an oxygen water quality evaluation. A digital bathymetric map of the estuary was compiled to enable volume-weighted calculations of physical and chemical properties. A seasonally variable data set was available to determine the effects of summer/winter and high-/low-runoff conditions on the oxygen concentrations of the waters. Using the freshwater input rates and the observed salinity distribution in the estuary we calculated the transport of waters between boxes and the residence times of water within each box. The model was applied to oxygen concentrations in the estuary incorporating estimates of the effects of air-sea exchange, of sediment oxidation demand, of photosynthetic production and respiratory consumption, and of biochemical oxygen demand from sewage treatment effluents. The model provides a basis to estimate the relative importance of various processes that may cause low oxygen conditions in the waters.

An investigation of oxygen variations in coastal waters was conducted with an Endeco/YSI rapid-pulse dissolved oxygen electrode. A 30-day time series was obtained at a depth of 1-2 m in Narragansett Bay. Measurements of oxygen, temperature, and salinity were obtained every 30 min during October 1993. Fourier analyses were used to determine the frequencies in the oxygen, temperature, and meteorological (wind speed and sunlight levels) variables. There was a strong diel signal in oxygen with smaller amplitude variations at the semidiurnal tidal frequency and a large amplitude variation with a period of 3-5 days. High temporal resolution data are needed to detect the events in coastal waters that result in substantial chemical variations of biologically active constituents such as oxygen.

In anticipation of possible applications of the next generation ocean color satellite sensor, SeaWiFS, we have been examining the historical CZCS data from the region off the northeastern U.S.A. We have worked with both the 4-km and the l-km horizontal resolution CZCS data. The scales of variability that are evident are in the range of 5-50 km. For quantitative use of the ocean color data attention must be given to spatial variations in the atmospheric attenuation of the visible radiation, and to the separation of chlorophyll, suspended matter, and possibly blue-absorbing organic matter in the ocean color signal.

MARINE CHEMISTRY 53: (1-2) 131-145 JUL 1996

Abstract: A new automated observatory dedicated to the radiometry of the moon has been constructed to provide new radiance information for calibration of earth-orbiting imaging instruments, particularly Earth Observing System instruments. Instrumentation includes an imaging photometer with 4.5-in. resolution on a fully digital mount and a full-aperture radiance calibration source. Interference filters within 0.35-0.95 mu m correspond to standard stellar magnitude systems, accommodate wavelengths of lunar spectral contrast, and approximate some bandpasses of planned earth-orbiting instruments (ASTER, Landsat-7 ETM, MISR, MODIS, and SeaWIFS).

The same equipment is used for lunar and stellar observations, with the use of an aperture stop in lunar imaging to comply with Nyquist's theorem and lengthen exposure times to avoid scintillation effects. A typical robotic night run involves observation of about 60 photometric standard stars and the moon; about 10 of the standard stars are observed repeatedly to determine atmospheric extinction, and the moon is observed several times. Observations are to be made on every photometric night during the bright half of the month for at least 4.5 years to adequately cover phase and libration variation. Each lunar image is reduced to absolute exoatmospheric radiance and reprojected to a fixed selenographic grid system. The collection of these images at various librations and phase angles will be reduced to photometric models for each of the approximately 120 000 points in the lunar grid for each filter. Radiance models of the moon can then be produced for the precise geometry of an orbiting instrument observation. Expected errors are under 1% relative and 2.5% absolute. A second telescope operating from 1.0 to 2.5 mu m is planned.

JOURNAL OF ATMOSPHERIC AND OCEANIC TECHNOLOGY 13: (2) 360-375 APR 1996

Key Words: Bidirectional Reflectance Spectroscopy, Atmospheric Extinction, Absolute Calibration, Energy Distribution, Alpha-Lyrae, Stars, Photometry, Transformation, Ephemerides, Library

Abstract: A methodology for delineating the influence of finite spectral bandwidths and significant out-of-band response of sensors for remote sensing of ocean color is developed and applied to the Sea-viewing Wide-Field-of-view Sensor (SeaWiFS). The basis of the method is the application of the sensor's spectral-response functions to the individual components of the top-of-the-atmosphere (TOA) radiance rather than the TOA radiance itself. For engineering purposes, this approach allows one to assess easily (and quantitatively) the potential of a particular sensor design for meeting the system-sensor plus algorithms-performance requirements. In the case of the SeaWiFS, two significant conclusions are reached. First, it is found that the out-of-band effects on the water-leaving radiance component of the TOA radiance are of the order of a few percent compared with a sensor with narrow spectral response. This implies that verification that the SeaWiFS system-sensor plus algorithms-meets the goal of providing the water-leaving radiance in the blue in clear ocean water to within 5% will require measurements of the water-leaving radiance over the entire visible spectrum as opposed to just narrow-band (10-20-nm) measurements in the blue. Second, it is found that the atmospheric correction of the SeaWiFS can be degraded by the influence of water-vapor absorption in the shoulders of the atmospheric-correction bands in the near infrared. This absorption causes an apparent spectral variation of the aerosol component between these two bands that will be uncharacteristic of the actual aerosol present, leading to an error in correction. This effect is dependent on the water-vapor content of the atmosphere. At typical water-vapor concentrations the error is larger for aerosols with a weak spectral variation in reflectance than for those that display a strong spectral variation. If the water-vapor content is known, a simple procedure is provided to remove the degradation of the atmospheric correction. Uncertainty in the water-vapor content will limit the accuracy of the SeaWiFS correction algorithm.
© 1995 Optical Society of America

APPLIED OPTICS 34: (36) 8363-8374 DEC 20 1995

Key Words: Phytoplankton, Scanner, Scattering

Abstract: The SeaWiFS potential for identifying the marine cyanobacterium Trichodesmium, at low concentration in oligotrophic case 1 waters, has been investigated by numerical simulations using a three-component model of sea colour. The results obtained indicate that simple algorithms, which operate on data recorded by SeaWiFS bands 2, 3, and 5, should have the capability to discriminate pixels containing Trichodesmium at concentrations as low as 0.1-0.3 mg m(-3) chlorophyl a, as well as to yield an estimate of the concentration. The validity range of the procedure has been explored by a sensitivity analysis, assuming realistic variations in the input data to the optical model.

INTERNATIONAL JOURNAL OF REMOTE SENSING 16: (18) 3619-3627 DEC 1995

Key Words: Ocean Color, Phytoplankton Pigments, Coastal Waters, North-Atlantic, Absorption, Spectra, Matter

Abstract: About 300 coastal zone color scanner (CZCS) scenes, gathered over the eastern Mediterranean basin mostly during the years 1979-1981, have been processed from level 1 by using improved pixel-by-pixel procedures for the atmospheric correction and pigment retrieval. The seasonal evolution of the upper ocean pigment concentration is described and analyzed within the whole basin and its subbasins. From the chlorophyll concentration in the top layer, and by using statistical relationships, the depth-integrated pigment content is estimated and used in conjunction with a light-photosynthesis model to estimate the carbon fixation. The model relies on a set of physiological parameters, selected after the validation of the light-photosynthesis model and not on locally measured parameters. Additional information needed in the modeling are the photosynthetically available radiation (computed from astronomic and atmospheric parameters, combined with a cloud climatology), sea temperature and mixed-layer depth (taken from Levitus (1982)). Actually, the model is used to generate look-up tables in such a way that all possible situations (concerning available radiation, chlorophyll concentration, and temperature) are covered. The appropriate situation associated with any pixel is selected from these tables to generate primary production maps. Despite a relatively good spatial coverage, studying the interannual variability of the pigment distribution and primary production appeared to be impossible. Therefore 12 ''climatological'' monthly chlorophyll maps have been produced by merging the data corresponding to several years. The carbon fixation rates in each of the subbasins have been computed on a monthly basis, and annual mean values derived thereafter. The primary production values are compared with sparse field determinations. They are also compared with those previously derived for the Western basin, also by using CZCS data (Morel and Andre, 1991). When put together, these companion works provide a kind of record of the trophic status of the entire Mediterranean Sea in the early 1980s. Ocean color sensors to be launched next, like SeaWIFS, will allow the seasonal and interannual variabilities in the late 1990s to be addressed.

JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 100: (C8) 16193-16209 AUG 15 1995

Key Words: Particulate Organic-Matter, Oceanic Primary Production, Phytoplankton, Sea, Nutrients, Light, Photosynthesis, Transparency, Variability, Dynamics

Abstract: Nitrogen-limited estuaries, shallow coastal and continental shelf waters account for nearly half the global oceanic primary production. Accelerating primary production, or eutrophication, of these waters appears linked to increasing anthropogenic N loading. Among loading sources, atmospheric nitrogen deposition (AND) (as wet- and dryfall) is of considerable and increasing importance (100 to over 1000 mgN . m-2 . yr(-1)). Current contributions of AND to total external N loading range from 10 to over 50%. AND may play a central role in mediating ''new'' production in coastal oceans downwind of emissions. Examples of AND-impacted waters include: US Atlantic coastal waters, where atmospheric N inputs can significantly enhance CO₂ fixation and chlorophyll a production, the Baltic and North Seas, the Canadian Atlantic seaboard, and the Western Mediterranean Sea. Recent increases in toxic and non-toxic phytoplankton blooms in these waters may be linked to accellerating nutrient loading at the land-sea interface; a significant fraction of it attributable to AND. This hitherto-neglected nutrient-production interaction requires evaluation on regional and larger synoptic scales. Aircraft and satellite-based ocean color remote sensing (i.e. SeaWiFS) will be useful in characterizing and linking the spatial-temporal interactions of this and other >>new<< nutrient inputs with eutrophication of estuarine and coastal waters.

OPHELIA 41: 237-259 MAR 1995

Key Words: Chlorophyll-A Production, Stream Surface Seawater, North-Sea, Trophic Implications, Nutrient Limitation, Marine-Environment, Organic Nitrogen, Chesapeake Bay, Deep Ocean, Acid-Rain

Abstract: We present a simple modification to the standard coastal zone color scanner (CZCS) atmospheric correction algorithm for application to Sea-viewing-wide-field-of-view-sensor (Sea WiFS). The modification reduces the error in the water-leaving reflectance using the standard algorithm by a factor of 2-6 when the aerosol behaves as predicted by the LOWTRAN-6 models. For many aerosol models likely to approximate aerosol properties over the oceans the error in the retrieved water-leaving reflectance is predicted to be less than or similar to +/- 0.002 at 443 nm for an aerosol load approximately 2 to 3 times that normally occurring in a maritime atmosphere. These errors in atmospheric correction lead to an error in the pigment concentration (C), retrieved using the blue-green ratio algorithm, of less than or similar to 50% for more than 75% of the aerosol models tested, whenever the algorithm retrieves a ''reasonable'' pigment concentration, and when 0.1 less than or equal to C less than or equal to 1 mg/m(3). This accuracy may be sufficient for some applications, for example, at-sea processing to guide ships to desirable sampling locations. An important feature of this algorithm is that, unlike more sophisticated and computational intensive algorithms, aerosol models are not required to effect the actual atmospheric correction. Investigators already having the CZCS algorithm implemented on an image processing system should be able to process Sea-WiFS imagery by making very simple modifications to the code.

REMOTE SENSING OF ENVIRONMENT 50: (3) 231-239 DEC 1994

Key Words: Coastal Zone Color Scanner, Surface-Roughness Considerations, Ocean Color, Phytoplankton Pigments, Imagery, Sensors, Radiances, Whitecaps

Abstract: The effects of oceanic whitecaps on ocean-color imagery are simulated and inserted into the proposed Sea-Viewing Wide-Field-of-View Sensor (SeaWiFS) atmospheric-correction algorithm to understand its tolerance to error in the estimated whitecap contribution. The results suggest that for wind speeds less than or equal to 10-12 m/s, present models that relate whitecap reflectance to wind speed are sufficiently accurate to meet the SeaWiFS accuracy goal for retrieval of the water-leaving radiance in the blue, when the aerosol scattering is weakly dependent on wavelength. In contrast, when the aerosol scattering has a strong spectral signature, the retrievals will meet the goal only when the whitecap reflectance is underestimated.

APPLIED OPTICS 33: (33) 7754-7763 NOV 20 1994

Key Words: Wind-Speed, Scanner, Surface, Imagery, System

Abstract: We investigate the influence of the curvature of the Earth on a proposed atmospheric-correction scheme for the Sea-Viewing Wide-Field-of-View Sensor (SeaWiFS) by simulating the radiance exiting the top of a spherical-shell atmosphere and inserting the result into the proposed correction algorithm. The error in the derived water-leaving reflectance suggests that the effects of the curvature are negligible for solar zenith angles (theta0) less-than-or-equal-to 70-degrees. Furthermore, for theta0 > 70-degrees the error in atmospheric correction can ususally be reduced if the molecular-scattering component of the top of the atmosphere reflectance (rho(r)) is computed with a spherical-shell atmosphere radiative transfer code. Also, for theta0 > 70-degrees the error in atmospheric correction in a spherical-shell atmosphere, when rho(r) is computed with a spherical-shell model, can be predicted reasonably well from computations made with plane-parallel atmosphere radiative transfer codes. This implies that studies aimed at improving atmospheric correction can be made assuming plane-parallel geometry and that the investigator can be confident when theta0 > 70-degrees that any improvements will still be valid for a spherical-shell atmosphere as long as rho(r) is computed in spherical-shell geometry. Finally, a scheme for computing rho(r) in a spherical-shell atmosphere in a relatively simple manner is developed.

APPLIED OPTICS 33: (30) 7096-7106 OCT 20 1994

Key Words: Surface-Roughness Considerations, Scanner, Imagery, System

Abstract: Algorithms that use the SeaWiFS radiometer band reflectance data for the retrieval of phytoplankton pigment concentration, suspended sediment concentration, and yellow substance absorption in coastal water are set up by a computation based on a three-component model of sea color. The varying coastal environment is characterized by a site-specific correlation among the three parameters, subjected to large spatial and temporal fluctuations. The computation is performed with respect to the summer situation of the Gulf of Naples (Mediterranean Sea). The sensitivity of the retrieval of each parameter to variations in the concentration of the two other quantities is investigated by numerical simulations. The sensitivity to the variability of the absorption and scattering properties of phytoplankton and suspended sediment is analyzed, as well as the error induced by the uncertainty of the remote-sensing data. The algorithms's performance is satisfactorily tested on sets of SeaWiFS band reflectances randomly generated within wide water composition ranges. Although the results obtained cannot be generalized and require experimental validation, the series of tests performed suggests that the proposed algorithms, with numerical constants adjusted to the lcoal conditions, can be effectively applied to several types of coastal environment.

APPLIED OPTICS 33: (12) 2369-2378 APR 20 1994

Key Words: Matter, Sea

Abstract: The importance of tilt capability for sun glint avoidance for future global ocean color missions was analyzed. The analyses focused on Sea-viewing Wide Field-of-view Sensor (SeaWiFS) mission, because its radiometric, orbital, and sensor characteristics are well defined. The analyses concentrated on two major questions: 1) does tilting to avoid sun glint increase or decrease the total ocean coverage, and 2) at high latitudes far from the region of maximum sun glint, should the sensor be tilted or untilted?

For ocean coverage maximization, if the sensitivity of ocean color algorithms to sun glint is of the same order as the error in the atmospheric correction algorithms, then a tilted sensor produces nearly 20 percent better coverage than an untilted one after 2 d in the absence of clouds, and 12 percent after 4 d including clouds. Thus, the tilt capability can improve the ocean coverage of future ocean color missions.

At high latitudes differences in transmitted water-leaving radiance between tilted and untilted sensors were well within the algorithm errors. Furthermore, sun glint radiances exceeding the algorithm errors occurred at high wind speeds as far as 70-algorithms from the solar declination, suggesting that sensors should remain in the tilted mode up to this limit.

IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING 32: (4) 866-877 JUL 1994

Key Words: Optical-Properties, Natural-Waters, Model, Atmospheres, Irradiance, Scattering, Radiance, Aerosol, Scanner

Abstract: This report details the South African involvement in satellite remote sensing of ocean colour and thermal signatures. We outline the South African ocean-colour and upwelling experiment, thermal infra-red imagery, and calibration and algorithm development, as a tool for oceanographic research around and south of the South African coast. We also describe the contribution satellite remote sensing of ocean colour and surface chlorophyll may make to international climate-change programmes. The acceptance of south Africa's proposal, by the National Aeronautics and Space Administration (NASA), for the forthcoming Sea Viewing, Wide field-of-view Sensor (SeaWiFS) ocean-colour project provides new opportunities and responsibilities for satellite remote sensing in South Africa in the future, which we also discuss, particularly with respect to national and international climate-change programmes.

SOUTH AFRICAN JOURNAL OF SCIENCE 90: (1) 37-44 JAN 1994

Key Words: Sub-Tropical Convergence, Benguela Current Region, Agulhas Current, Thermocline Water, Upwelling Front, Atlantic-Ocean, Current System, Retroflection, Circulation, Features

Abstract: During its lifetime the coastal zone color scanner (CZCS) produced approximately 66,000 images. These have been placed in an archive of ''raw'' radiance (sensor counts) in a subsampled format that is easily accessible. They have also been processed to form global fields, at reduced resolution, of normalized water-leaving radiance, phytoplankton pigments, and diffuse attenuation coefficient. Using this archive, we have tried to characterize some aspects of the ''system calibration'' for the 8-year lifetime of CZCS. Specifically, we have assumed that the sensitivity of the red band decayed in a simple manner similar to the well-known long-term degradation of the shorter-wavelength bands, and we examined the sensitivity of the green and yellow bands by computing the globally averaged water-leaving radiance, over 10-day periods, for all of the imagery. The results provide evidence that in addition to the long-term degradation, short-term (2 weeks to 1 month) variations in the radiometric sensitivity of these bands started in early fall 1981 and continued for the rest of the mission. In contrast, the data suggest the absence of such variations prior to August 1981. It is reasonable to believe that the sensitivity of the blue (and probably the red) band underwent such variations as well; however, our methodology cannot be used to study the other bands. Thus after these fluctuations began, the actual values of CZCS-estimated pigment concentrations at a given location should be viewed with skepticism; however, the global patterns of derived pigment concentration should be valid. Had an extensive set of surface measurements of water-leaving radiance, e.g., from moored buoys or drifters, been available during the CZCS mission, these fluctuations could have been removed from the data set, and this would have greatly increased its value. The lessons learned from CZCS, that is, the requirement of good radiometric calibration and stability and the necessity of ''sea truth'' stations to monitor the performance of the system (sensor plus algorithms), are being applied to the sea-viewing wide-field-of-view sensor (SeaWiFS) scheduled for launch in August 1993.

JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 99: (C4) 7293-7307 APR 15 1994

Key Words: Surface-Roughness Considerations, Atmospheric Correction, Ocean Color, Radiometric Sensitivity, Phytoplankton Pigments, Remote Sensors, NIMBUS-7 CZCS, Scattering, Imagery, Radiances

Abstract: The Caribbean Sea is an area that traditionally has been considered oligotrophic, even though the Orinoco River contributes large quantities of fresh water, nutrients, and other dissolved materials to this region during the wet boreal (fall) season. Little is known about the impact of this seasonal river plume, which extends from Venezuela to Puerto Rico shortly after maximum discharge. Here we present results from a study of the bio-optical characteristics of the Orinoco River plume during the rainy season. The objective was to determine whether the coastal zone color scanner (CZCS) and the follow-on sea-viewing wide-field-of-view sensor (SeaWiFS) satellite instrument can be used to assess the concentrations of substances in large river plumes. Recent in situ shipboard measurements were compared to values from representative historical CZCS images using established bio-optical models. Our goal was to deconvolve the signatures of colored dissolved organic carbon and phytoplankton pigments within satellite images of the Orinoco River plume. We conclude that the models may be used for case II waters and that as much as 50% of the remotely sensed chlorophyll biomass within the plume is an artifact due to the presence of dissolved organic carbon. Dissolved organic carbon originates from a number of sources, including decay of dead organisms, humic materials from the soil, and gelbstoff.

JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 99: (C4) 7443-7455 APR 15 1994

Key Words: Dissolved Organic-Matter, Optical Classification, Natural-Waters, North-Atlantic, Ocean Color, Model, Sea

Abstract: A coupled atmosphere and ocean radiative transfer model, the Gulf of Maine (GOM) model, was developed to simulate water-leaving radiance from a vertically stratified ocean containing a bloom of the coccolithophore Emiliania huxleyi. The model is based largely on atmospheric and ocean data representing the Gulf of Maine. The atmospheric submodel simulates direct sunlight and diffuse skylight illuminating the sea surface and is adjusted to account for seasonal changes in atmospheric aerosols. The optical properties of E. huxleyi, required by the ocean submodel, are derived from measurements collected in Gulf of Maine coccolithophore blooms occurring in 1989 and 1990. The modeled response of volume reflectance to the combined effects of chlorophyll and particulate calcite compares favorably with field measurements of E. huxleyi cell abundance and coastal zone color scanner (CZCS)-derived volume reflectance representing a coccolithophore bloom in the northeast Atlantic Ocean. The GOM model was used to investigate the response of normalized water-leaving radiance, modeled for visible CZCS and sea viewing wide field of view sensor (SeaWiFS) bands, to particulate calcite and chlorophyll a. Ranges in the concentrations of particulate calcite, chlorophyll a, and colored dissolved organic material (CDOM) are selected to represent conditions reported for coccolithophore blooms. Water-leaving radiance increases with increasing particulate calcite concentration, primarily because of a disproportionately large amount of backscatter from detached coccoliths (about an order of magnitude larger than is predicted using Mie theory). As a result, CZCS plant pigment algorithms based upon radiance ratios may be corrupted more severely than previously estimated. As an alternative to radiance ratio-based algorithms, an iterative procedure (also referred to as optimization) is used to invert the GOM model in order to simultaneously retrieve particulate calcite and chlorophyll a concentrations. The approach uses normalized water-leaving radiance computed for all visible CZCS or SeaWiFS bands. Tests of the approach suggest that independent of errors associated with instrument calibration and atmospheric correction, errors in the retrieved concentrations are small, even when high concentrations of CDOM and vertical structure within the water column are neglected, i.e., with the assumptions that CDOM concentration is small and the water is vertically homogeneous. However, since there are no data sets of contemporaneous chlorophyll a concentration, particulate calcite concentration, and CZCS imagery, a rigorous test of the model and inversion technique must wait for the launch of new ocean color scanners such as the NASA SeaWiFS.

JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS 99: (C4) 7483-7499 APR 15 1994

Key Words: Dissolved Organic-Matter, Optical-Properties, Irradiance Model, Ocean Color, Phytoplankton, Scattering, Absorption, Atmospheres, Satellite, Surface

Abstract: Passive ocean-color data at 32 wavelengths in the visible domain and laser-induced fluorescence line heights of chlorophyll and phycoerythrin, measured simultaneously from an aircraft in the New York Bight area, are used to examine the problem of developing algorithms for pigment retrieval from ocean-color data that would be capable of distinguishing between chlorophyll and phycoerythrin. Using factor analysis, it is shown that it is indeed possible to develop such algorithms. Furthermore, the wavelengths used in the algorithms can be reduced from 32 to 6 (similar to the SeaWiFS channels) without much loss in information. These multiwavelength algorithms yield significantly higher correlation coefficients for chlorophyll compared with the conventional blue-green ratio used for retrieval of this pigment. The Coastal Zone Color Scanner wavelengths appear to be inadequate for quantitative retrieval of the phycoerythrin signal.

APPLIED OPTICS 33: (6) 1081-1089 FEB 20 1994

Key Words: Atlantic Bight, Chlorophyll, Satellite, Water, Dinoflagellate, Reflectance, Model

Abstract: Approximately half of the world's ocean ic primary production originates in coastal waters wh ich are often nitrogen (N) limited and sensitive to externally supplied N. Among anthropogenically generated N sources, atmospheric deposition of N (ADN) (as wet- and dryfall) contributes 10-50% of the total external N load at present (20-100 mmol N.m(-2).yr(-1)), and this will increase. At current levels, atmospheric N inputs lead to a significant enhancement of CO₂ fixation and chlorophyll a production. ADN may play a central role in mediating ''new'' production in coastal oceans downwind of emissions. Alterations in productivity, nutrient flux, and trophic changes have recently been documented from the Baltic and North seas, the Northwest Atlantic seaboard, and the Western Mediterranean. The recently noted ''epidemic'' of toxic and nuisance phytoplankton blooms is possibly due to accelerating nutrient loading inshore, especially from atmospheric sources. A need exists to spatially and temporally evaluate, quantify, and potentially manage this nutrient-production interaction on regional and larger synoptic scales. Aircraft- and satellite-based multiband ocean color remote sensing (SeaWiFS) will help characterize and link the spatial-temporal interactions of this (and other) ''new'' nutrient inputs with biogeochemical and trophic changes in coastal and offshore waters.

CANADIAN JOURNAL OF FISHERIES AND AQUATIC SCIENCES 50: (10) 2254-2269 OCT 1993

Key Words: Free Amino-Acids, Nutrient Limitation, Phytoplankton Growth, Marine Ecosystems, Organic-Matter, Pacific-Ocean, North-Sea, Inorganic Nitrogen, Chesapeake Bay, Natural-Waters

Abstract: The second generation of ocean-color-analyzing instruments requires more accurate atmospheric correction than does the Coastal Zone Color Scanner (CZCS), if one is to utilize fully their increased radiometric sensitivity. Unlike the CZCS, the new instruments possess bands in the near infrared (NIR) that are solely for aiding atmospheric correction. We show, using aerosol models, that certain assumptions regarding the spectral behavior of the aerosol reflectance employed in the standard CZCS correction algorithm are not valid over the spectral range encompassing both the visible and the NIR. Furthermore, we show that multiple-scattering effects on the algorithm depend significantly on the aerosol model. Following these observations, we propose an algorithm that utilizes the NIR bands for atmospheric correction to the required accuracy. Examples of the dependence of the error on the aerosol model, the turbidity of the atmosphere, and surface roughness (waves) are provided. The error in the retrieved phytoplankton-pigment concentration (the principal product of ocean-color sensors) induced by errors in the atmospheric correction are shown to be <20% in approximately 90% of the cases examined. Finally, the aerosol thickness (tau(alpha)) is estimated through a simple extension of the correction algorithm. Simulations suggest that the error in the recovered value of T(alpha) should be less than or similar to 10%.

APPLIED OPTICS 33: (3) 443-452 JAN 20 1994

Key Words: Coastal Zone Color Scanner, Surface-Roughness Considerations, Atmospheric Correction, Phytoplankton Pigments, Cloud Albedo, Satellite, Scattering, Imagery, Turbidity, Particles

Abstract: In a variety of remote sensing applications inverse modeling is used to retrieve parameters of our environment from measurements of the radiance spectrum. As the dimensionality of the data increases with the number of spectral channels or as models become more complicated, inverse modeling becomes expensive in terms of computing time. We describe a technique to parameterize a given inverse model, which reduces the necessary computing time by orders of magnitude. An example that uses simulated data of SeaWiFS, an advanced ocean color sensor to be launched in 1993, is given, whereby the concentrations of suspended matter, phytoplankton, and gelbstoff (yellow substance) in water are determined.

APPLIED OPTICS 32: (18) 3280-3285 JUN 20 1993

Key Words: Coastal, Matter

Abstract: The Sea-viewing Wide Field-of-view Sensor (SeaWiFS) will be the first ocean color satellite since the Nimbus-7 Coastal Zone Color Scanner (CZCS), which ceased sending data in 1986 after more than seven years of operation. Unlike the CZCS, which was conceived as a proof-of-concept experiment, SeaWiFS will provide routine global coverage every two days and is designed to provide estimates of photosynthetic pigment concentrations of sufficient accuracy for use in quantitative studies of the ocean's primary productivity and biogeochemistry. The SeaWiFS instrument is described within a comparative review of the CZCS mission, from which the many design features employed to improve radiometric accuracy and minimize instrumental effects are elucidated. The former includes the use of solar and lunar calibration signals, and an internal electric signal to track long-term gain shifts, while the latter includes detector nonlinearity, offsets, bright target recovery, parasitic response, filter spectral shifts with temperature and humidity, out-of-band radiation, polarization sensitivity, stray light, mirror coating degradation, coherent noise, and electromagnetic interference (EMI) effects.

MARINE TECHNOLOGY SOCIETY JOURNAL 27: (1) 3-15 SPR 1993

Key Words: Scanner, NIMBUS-7, Phytoplankton, Calibration, Imagery, Ship

Abstract: Computed geophysical fields from a 3-D general circulation model are coupled with the Coastal Zone Color Scanner (CZCS) satellite data on chlorophyll content of surface ocean waters. The CZCS satellite data on chlorophyll content of surface ocean waters are used to estimate the 'photochemical lability' of dissolved organic matter in the surface ocean. Monthly estimates are made of the global ocean to atmosphere flux of a biogeochemically important gas, carbonyl sulfide (OCS), with 2.8-degrees x 2.8-degrees latitude-longitude spatial resolution. This novel technique provides a conceptual and computational method for integrating data collected as part of future satellite measurement campaigns, such as the Earth Observing System (EOS) and Sea-viewing Wide-field-of view Sensor (SeaWiFS), with 3-D chemistry-climate prediction models.

GEOPHYSICAL RESEARCH LETTERS 20: (8) 683-686 APR 23 1993

Key Words: Carbonyl Sulfide, Surface Waters, Ocean, CO₂