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Data Format Specifications


Level-1A Data Products

Level-1A products contain the raw radiance counts from all bands as well as spacecraft and instrument telemetry. Calibration and navigation data, and instrument and selected spacecraft telemetry are also included. Level-1A data are used as input for geolocation, calibration, and processing.

The MODIS Level-1A format specifications can be found here: MODIS Level-1A format.

The SeaWiFS Level-1A format specifications can be found here: SeaWiFS Level-1A format.

The CZCS Level-1A format specifications can be found here: CZCS Level 1A format.


SeaWiFS Level-1A Browse Products

Each Level-1A browse product is generated from a corresponding Level-1A GAC or HRPT product. The main data content of the product is a true-color image generated from subsampled, calibrated, Rayleigh-corrected data for bands 2, 5 and 6, stored as one byte per pixel. Each Level-1A browse product corresponds exactly in geographical coverage (scan-line and pixel extent) to that of its parent Level-1A product and is stored in one physical HDF file. The Level-1A browse images can be viewed here].


MODIS Level-1B Data Products

The Level 1B data set contains calibrated and geolocated at-aperture radiances generated from Level 1A sensor counts. Additional data are provided, including quality flags, error estimates, and calibration data.

Information on the MODIS Level-1B format specifications can be found here: MODIS Aqua Level 1B page.


Ocean Level-2 Data Products

Each Level-2 product is generated from a corresponding Level-1A product.The main data contents of the product are the geophysical values for each pixel,derived from the Level-1A raw radiance counts by applying the sensor calibration, atmospheric corrections, and bio-optical algorithms. Each Level-2 product corresponds exactly in geographical coverage (scan-line and pixel extent) to that of its parent Level-1A product and is stored in one physical HDFfile.

The standard Ocean Color product contains 12 geophysical values derived for each pixel: six water-leaving radiances for bands 1 to 6, the chlorophyll a concentration, the diffuse attenuation coefficient at band 3, the epsilon value for the aerosol correction of bands 7 and 8, the angstrom coefficient for bands 4 and 8, and the aerosol optical thickness at band 8. The standard SST product contains 11-micron and 4-micron (nighttime only) SST for each pixel. In addition, 32 flags are associated with each pixel indicating if any algorithm failures or warning conditions occurred for that pixel.

More detailed information on the Level-2 format specifications can be found in the Ocean Level-2 Data Product document.


Level-2 Browse Products

Each Level-2 browse product is generated from a corresponding Level-2 product. The main data contents of the product are a subsampled version of the chlorophyll-a image stored as one byte per pixel. Each Level-2 browse product corresponds exactly in geographical coverage (scan-line and pixel extent) to that of its parent Level-2 product and is stored in one physical HDF file. The Level-2 browse images can be viewed here

More detailed information on the Level-2 browse product format specifications can be found in the Ocean Level-2 Browse Product document.


Ocean Level-3 Binned Data Products

Level-3 binned data products consist of the accumulated data for all Level-2 data corresponding to a period of one day, 8 days, a calendar month, or a calendar year.

Each Level-3 binned data product is stored in one or more HDF files. Each multi-file product includes a main file containing all product-level metadata and data for each bin that are common to all the binned geophysical parameters, and multiple subordinate files, each of which contains data of one binned geophysical parameter for all bins. Subordinate files must be read in conjunction with the associated main file.

More details:SeaWiFS Level 3 Binned details

More details:MODIS Level 3 Binned details

More detailed information on the Level-3 data product format specifications can be found in the Ocean Level-3 Binned Data Products document.


Ocean Level-3 Standard Mapped Image Products

The Level-3 standard mapped image (SMI) products are image representations of binned data products generated from SeaWiFS, MODIS, OCTS or CZCS data. The data in each SMI product represents an image of the parameter specified by the global attribute Parameter. This object is a two-dimensional array of an Equidistant Cylindrical (also known as Platte Carre) projection of the globe. The values can be stored as bytes, 2-byte integers, or 4- byte floats. The first two are scaled real values and may be converted projected to geophysical values using the global attributes Scaling, Scaling Equation, Base, Slope, and Intercept.

Actual SMI files can be downloaded from our level-3 browser.

The standard SMI products are generated from binned data products, one for each of the following geophysical parameters: chlorophyll a concentration, angstrom coefficient, normalized water-leaving radiance at each visible wavelength, aerosol optical thickness, epsilon, and diffuse attenuation coefficient at 490 nm. For MODIS, products are generated for sea surface temperature (SST), 4 micron SST (SST4) and nighttime SST (NSST). Thus, each SMI product represents data binned over the period covered by the parent product. The arithmetic mean is used in each case to obtain the values for the SMI grid points from the binned data products. Each SMI product contains one image of a geophysical parameter and is stored in one physical HDF file.

More detailed information on the Level-3 Standard Maped Image data product format specifications can be found in the Ocean Level-3 SMI Data Products document.


Near Real-Time Ancillary Data Products

Products of the meteorological data--meridional wind, zonal wind, pressure, and relative humidity--and total ozone, used during the Level-2 operational processing, are made available by the Project. (Relative humidity is not currently used during the processing.) The meteorological and ozone data are referred to as ancillary data. These products are gridded, Equidistant Cylindrical images of, or derived from, data from other agencies. These data represent global "snapshots" at frequencies of at least once per day and as suchare considered as near real-time (NRT) data. Each product is contained in one physical HDF file.

As part of its quality control procedures, the Project may modify suspect valuesand fill missing values of NRT ancillary data grid points. An associated "Q/C" field is stored with each ancillary parameter image for recording any modifications to the original data. If a grid point's ancillary data value is changed, the corresponding Q/C grid point is set equal to 1; otherwise, it is set equal to 0.


Climatological Ancillary Data Products

Climatologies of the ancillary data required for Level-2 processing have been created by the SeaWiFS Project. These climatologies can be used by the Level-2 processing software in lieu of NRT data when the NRT data are unavailable or deemed to be of poor quality.

Two climatological products, each a single HDF file, are used--one for four meteorological parameters and the other for ozone. For each of these five parameters, long-term monthly means were calculated using data from other agencies. The means, along with the associated standard deviations and number of observations, are stored as gridded, Equidistant Cylindrical images.


SeaWiFS Sensor Calibration Table

The sensor calibration table is comprised of a set of parameters required for applying the sensor calibration to raw (Level-1A) data. The table is stored as one physical HDF file that is available as a SeaWiFS product.

The calibration table includes parameters that will not be changed and parameters that may be updated. Updates are performed by the SeaWiFS Project and result in the appending of data to the file's contents. Whenever it is updated, a new version of the file is made available as a product. Results of vicarious calibration studies can indicate if updates are needed to improve previous calibration parameter values or to account for changes in sensor

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Updated: 09 November 2010