(gene@seawifs.gsfc.nasa.gov) (301) 286-9428 Last updated 30 March 2000
| GSFC | |
| SeaWiFS Project | Telephone: (301) 286-9676 |
| Code 970.2 | Fax: (301) 286-0268 |
| NASA | Internet: seawifs_info@seawifs.gsfc.nasa.gov |
| Goddard Space Flight Center | |
| Greenbelt, MD 20771 USA | |
| Dr. Charles McClain, | Project Manager/Project Scientist |
| Dr. Gene Feldman, | Data Systems Manager |
| GSFC DAAC User Support | Telephone: (301) 614-5224 |
| Code 902 | Toll Free: 1-877-794-3147 |
| NASA | Fax: (301) 614-5268 |
| Goddard Space Flight Center | Internet: daacuso@daac.gsfc.nasa.gov |
| Greenbelt, MD 20771 USA | |
| Ocean Color Data Support Team: | ocean@daac.gsfc.nasa.gov |
| Telephone: (301) 614-5435 | |
| Orbital Sciences Corporation | |
| Dr. John McCarthy | Telephone: (703) 406-5504 |
| SeaStar Program Manager | Fax: (703) 406-5461 |
| Orbital Sciences Corporation | Internet: jmcca@orbital.com |
| 21700 Atlantic Blvd. | |
| Dulles, VA 20166 USA | |
| NASA/HQ | |
| Dr. Janet Campbell | Telephone: (202) 358-0310 |
| Program Scientist, SeaWiFS | Fax: (202) 358-3098 |
| NASA | Internet: jcampbe1@mail.hq.nasa.gov |
| Washington, DC 20546 USA |
SeaWiFS will produce two types of science data: Local Area Coverage (LAC; 1.13 km nadir resolution) of ocean color will be direct broadcast and selectively recorded, while Global Area Coverage (GAC; subsampled on board every fourth line, every fourth pixel) will be recorded on board the SeaStar spacecraft. Direct broadcast LAC will be routinely received at GSFC for the U.S. East Coast as part of the project mission assurance effort. Other encrypted LAC data may be received at approved NASA Space Act Agreement research direct readout stations around the world, funded by non-NASA sources, which obtain NASA Space Act Agreements in accordance with this Dear Colleague letter. Decryption codes for research ground stations will be provided no sooner than two weeks after data capture. A coverage mask for the GSFC ground station is provided in Figure 1.
In order to meet the science goals, the Project objectives are to
obtain full GAC coverage every two days. This requires nearly complete
use of on board recorder capacity. The limited onboard memory for LAC
recording will be allocated, in priority order, to essential sensor
monitoring functions, obtaining calibration data from diffuser plate
and lunar observations, remote coverage of key
Figure 2 shows the SeaWiFS Project and external elements within an end-to-end system overview. The elements of the SeaWiFS Project are the Science Data Processing System (SDPS), the Calibration and Validation Support System, the GSFC Mission Operations, the Data Capture Facility (DCF), the Project Scientist, and the Project Manager. External elements include Orbital Sciences Corporation (OSC), the GSFC Version-0 Distributed Active Archive Center (DAAC), Wallops Flight Facility (WFF), and research ground stations. The SeaStar satellite will broadcast encrypted SeaWiFS data in real time to the GSFC ground station, as well as to any ground station capable of receiving it. Recorded data---GAC and limited LAC---will be broadcast on a delayed basis to WFF and OSC. These recorded GAC and LAC data, LAC data collected from the GSFC direct readout research ground station, and selected LAC data from non-NASA ground stations will be transferred to the SDPS.
The SDPS element receives raw science data and generates the global ocean color data products. Within the SDPS are separate development, test, and production environments. Standard data products will be provided to GSFC's Version-0 DAAC, which will be responsible for archiving and distributing data.
The Calibration and Validation element develops algorithms and oversees the quality of the SeaWiFS data products and ancillary data (ozone, surface wind speeds, and atmospheric pressure) and generates analysis reports. It is responsible for establishing and updating calibration procedures for the SeaWiFS data, using correlative data for the validation of the higher level products, and performing trend and anomaly analysis.
The Mission Operations element serves as the Project's single point-of-contact for OSC and for the NASA Space Act Agreement research ground stations to communicate and coordinate scheduling and to report problems (W. Gregg, pers. comm.). The Mission Operations element also monitors telemetry and performs scheduling activities for scientific aspects of the mission operation. The Mission Operations element provides navigation information and orbital elements required for processing and data collection.
The Data Capture Facility operates and maintains the GSFC ground station, facilitates the delivery of recorded data from WFF to the SDPS, and provides bit and frame synchronization. The Project Scientist is responsible for scientific oversight, processing algorithm approval, and recorded GAC/LAC allocation arbitration. The Project Manager is responsible for overall project oversight and policy guidance.
Of the external elements, OSC is completely responsible for the space segment and command integration and uplink. WFF is the primary downlink station for recorded data, the DAAC is the distribution and archival facility, and research ground stations may receive direct broadcast SeaWiFS data in accordance with Appendix C.
The SeaWiFS Technical
Report Series
The SeaWiFS Program has been made possible, affordable, and timely due to its unique private vendor---data purchaser structure. As part of the contractual agreement between NASA and OSC for the ocean color data, NASA retains all rights to data for research purposes, and OSC retains all rights for commercial and operational purposes. There is an embargo period of two weeks from collection for general distribution of data to research users to protect OSC's commercial interests, and a five-year period after data capture before the data become public domain. Three exceptions to the two-week embargo include: a) field experiments requiring data for ship positioning, b) Application Demonstration Projects (ADPs) to prove feasibility and usefulness for operational purposes, and c) assessment of calibration/validation and instrument performance by NASA. Selection of cruises and ADPs for near-real time support will be made by NASA in consultation with the research community. During the five-year period, access will be permitted to the data for research purposes by authorized users. Data access for commercial or operational purposes will be denied by NASA. The data may be used without restraint five years after the data are collected.
Non-research users include commercial and operational users of data. The OSC contract defines commercial use as that involving the sale or resale of data, as well as data derived therefrom, for more than the cost of reproduction. Operational use is defined as routine real-time or close to real-time use of the data, as well as data derived therefrom, during the 14-day embargo period provided above, other than research exceptions that are expressly authorized by NASA.
Strict accounting must be kept for all users. This will include accounts of names of all authorized users, type and volume of data requested, and date and time of data distribution. This will help ensure that the SeaWiFS data will reach only authorized users for research. The accounting mechanisms will also keep track of the data distribution so that users can be notified when the sensor calibration, processing algorithms, or ancillary data used for producing the SeaWiFS products are revised. Updated authorized user lists will be maintained and distributed on electronic mail to allow users and ground station operators to keep within the bounds of the contractual agreement.
The GSFC DAAC has the responsibility to ensure the distribution of SeaWiFS data from NASA's archive to all approved SeaWiFS data users upon request. Authorized users may also request and receive LAC data archived at NASA Space Act Agreement ground stations. A consolidated, on-line, electronic catalog of all holdings of SeaWiFS data at GSFC and NASA Space Act Agreement ground stations may be accessed by all authorized SeaWiFS research users. Requests for data not held by the GSFC DAAC will be directed to the LAC station that holds the data. SeaWiFS data from any source will be provided at no more than the marginal cost of filling the specific request. The DAAC will support the distribution of data in its holdings through electronic means and on selected magnetic or optical media.
Table 1. SeaWiFS performance summary. Radiances are in units of mW cm-2 mm-1 sr-1
Band Wavelength Maximum Cloud Maximum Ocean SNR
FWHM (nm) Radiance Radiance
1 403-423 60.2 10.90 940
2 434-454 67.9 10.56 950
3 481-501 68.2 8.18 1160
4 499-521 66.5 7.16 1060
5 546-564 65.0 5.74 690
6 658-678 54.9 3.25 800
7 745-785 43.0 2.29 860
8 846-887 34.4 1.64 670
Barnes, R.A., W.L. Barnes, W.E. Esaias, and C.R. McClain, 1994:
Prelaunch Acceptance Report for the SeaWiFS Radiometer NASA TM 104566,
Vol. 22, 32 pp.
Spatial Resolution 1.1 km LAC and 4.4 km GAC
Radiometric Accuracy < 5 % absolute each band
Calibration/Stability Monitor solar diffuser (daily) lunar view (monthly)
Relative Precision < 1 % linearity of signal output to radiance
Between Band Precision < 5 % relative band-to-band, over 0.5 to 0.9 f.s.
Polarization Sensitivity < 2 % worst case, all scan and tilt angles
Dynamic Range 10 bit quantization; four gains each channel
Bright Target Recovery < 10 pixels
Scan Plane Tilt +20, 0, -20, within 30 seconds
Swath Width 2800 km (=B158-3=B0 LAC; =B145=B0 GAC)
Orbit Sun-synchronous, descending, 705 km, noon, 115 min.
Design Life > Five years
HRPT Frequency 1702.5 Mhz
Table 2. SeaWiFS standard data products.
Level-lA Unprocessed GAC and LAC data with calibration
and navigation information appended
Level-2 Pigment concentration (chlorophyll-a + phaeophytin)
Chlorophyll a concentration
Diffuse attenuation coefficient at 490 nm
Normalized water-leaving radiances (5)
Aerosol radiances (3)
Data quality flags
Level-3 Global gridded products (approximately 9 km
resolution) of Level-2 products at time averages
ranging from daily to monthly to annual periods
Table 3. Recommendations for a SeaWiFS ground station: minimum configuration
Given Satellite Parameters:
Sat. Transmitting Power ...................... 5 Watts
HRPT L-band frequencies ...................... 1698, 1707, 1702.5 Mhz
Frequency Stability .......................... 20 ppm
Modulation ................................... 67.5 Split-phase
Modulation Rate .............................. 0.6654-0.667 Mbps
Sat. Transmitter-Antenna Loss ................ 2.0 dB
Sat. Antenna Gain ............................ 2.8 dBiC
EIRP ......................................... 31 - 37 dBm
Slant Range .................................. 2900 km
Free Space Loss .............................. 166.1 dB
Fading and Rain Margin ....................... 0.5 dB
Ground Station Minimum Requirements
The requirements for Earth station systems can be classified into three
categories: Electrical, Mechanical and Overall performance. The main
Overall performance requirements are:
- High receiving antenna gain.
- Low noise temperature.
- Low sidelobe level from the interference standpoint.
- Low VSWR.
- High pointing and tracking accuracies.
- Compatible with environmental conditions.
- Good accessibility and ease of maintenance.
Electrical Performance:
.............................................. Suggested
Ground Antenna Diameter ...................... 5 ft
Ground Antenna Gain .......................... 28.5 dB
G/T Figure of Merit (5 degree) ............... 6.0 dB/K
Eb/No BER =3D 10E-6 including
implementation loss .................... 11.5 dB
Link Safety Margin ........................... 3 dB
Antenna Noise Temperature .................... 70 k
Mechanical Performance:
.............................................. Suggested
Angular Travel AZ ............................ 190 degree
EL ...................................... 0-180 degree
Angular Velocity AZ/EL ....................... 5 degree/sec
Angular Acceleration ......................... 30 degree/sec/sec
Backlash ..................................... 0.1 degree
Limit Switch ................................. AZ/EL
Pointing Accuracy ............................ 0.1 degree
Computational Precision ...................... 0.1 degree
Wind Survival (operational) .................. 50 mph
Wind Survival (Stall) ........................ 90 mph
Feed Polarization ............................ Circular
.............................................. LH & RH
LNA & Feed Line Length ....................... <10 ft
(should be integrated with feed)
LNA Gain ..................................... 30 dB
LNA/downconverter Noise Figure ............... 1.0 dB
Tracking Method .............................. Program
Tracking Program Error ....................... <6 sec/14 days
Archive System:
Data Storage (for real-time Users) .......... 600 Mbytes
Data Storage (for delayed users).............. 5 Gbytes
.............................................. 8 or 4 mm Tape Drive
Component Redundancy:
Weather Shielded ............................ Integrated feed and
.............................................. LNA/Downconverter
.............................................. 8 or 4 mm Tape Drive
Table 4. Example ground station link budget (PC/486 System) - Ingest only
Sat. Transmitter Power ....................... 5 Watts 6.98 dBw
SeaWiFS L-band frequency ..................... 1702.5 Mhz
Modulation ................................... Split-phase
Sat. Antenna TX Loss ......................... 2.0 dB
Sat. Antenna Gain ............................ 1.8 dBiC
EIRP ......................................... 31 dBm
Free Space Loss .............................. 166.1 dB
Bit Rate ..................................... 665.4 Kbps
Parabolic Antenna Dia ........................ 2.4 m (8 ft)
Ground Antenna Gain .......................... 29.5 dB
Ground Antenna Temp .......................... 70 k
Eb/No (BER =3D 10E-6) ........................ 10.5 dB
RF System Temp ............................... 270 k
Link Safety Margin ........................... 3 dB
G/T Figure of Merit .......................... 6.6 dB/k
C/T .......................................... -128.5 dBm/k
C/No.......................................... 70.1 dB
C/N........................................... 11.1 dB
Data Storage.................................. 330 MB IDE HD
.............................................. 4 mm Tape Drive
Front End System Configuration................ Bit Synchronizer
(Fit in PC expansion slots)
.............................................. Demodulator/Rec.
.............................................. Decommutator/Frame Formatter