The current chlorophyll product is stored as a 16bit scaled integer in the L2 and L3 data products. This produces some artifacts in the data products when the chlorophyll data are log-scaled, as is commonly done for histograms of chlorophyll. It was suggested that the chl product be stored as log(chl), so that these truncation artifacts would be minimized. This has implications for L3 binning, and so an alternative suggestion to store the chlorophyll product as floating point values has been adopted. This eliminates any truncation artifacts as the result of scaling the data. Figure 1 shows a global chlorophyll histogram for the scaled-integer case and Figure 2 shows the same data stored as floating point values. Notice the 'comb-tooth' effect at the low end in the scaled integer case is eliminated in the floating point case.
This change will add approximately 2MB to the size of a typical L2 GAC file. A typical file is ~28MB (uncompressed), with chlor_a stored as a floating point the size will be ~ 30MB.
When chlorophyll is stored as a scaled iteger value, there is an inhernt chlorophyll range of 0.001 - 64.767 mg/m3. This is not a limitation of the chlorophyll algorith, and so storing chlorophyll as floating point values will permit a much larger dynamic range. For the purposes of Level 3 binning, a modification to the CHLWARN flag (which is currently set for chlorophyll values < 0.01 and > 64.0) has been made. The new definition of the CHLWARN flag is to flag chlorophyll values > 100.0 mg/m3. This flag will also now be masked at Level 3.
During the evaluation phase of the SeaWiFS PAR product development, a number of enhancements were made to the algorithm which improved the agreement with in situ data. The updated algorithm, called version 1.2, was put into production at the end of March 2001. Data processed prior to that date will be reprocessed to reflect the current algorithm.
We are currently testing the generation of additional Level-3 binned ocean products with a 4.6 km bin size for 8-day and longer time scales. The current 9-km bin size was originally chosen to approximately match the maximum spacing of pixels at the edge of the GAC swath. For daily products, a small bin size would result in a sparsely filled grid. However, since the size and navigation accuracy of the GAC data is still 1 LAC pixel, it has been shown that it is possible to produce reasonable 4.6-km products (as does the MODIS Ocean team) over these time periods. This will be tested to see if the grid-filling and quality of the products is acceptable at this bin size. If acceptable, we will continue to produce the current suite of Level-3 binned and mapped products at the original 9 kilometer resolution and add an additional product suite at the MODIS 4.6 kilometer resolution.
Sample 4 kilometer monthly chlorophyll - September 2001 - (8640 pixels x 4320 lines, 7.4 megabyte jpeg)
We are working closely with Jacques Descloitres and Jim Tucker (GSFC Laboratory for Terrestrial Physics) on the development and validation of SeaWiFS land products. We will be producing 4.65 km gridded land products which will be transferred to the GIMMS group at GSFC for validation and distribution to the DAAC. The products will include NDVI, EVI, and surface reflectances. The software and algorithms have been finalized, and final validation runs are underway. The processing of SeaWiFS land products for the period from September 1997 to present has been completed and once the evaluation has been completed, the products will be made available at the Goddard DAAC.
Sample 4 kilometer monthly surface reflectance - September 2001 - (8640 pixels x 4320 lines, 2.5 megabyte jpeg)
