We are happy to announce the release of a new merged Level-3 chlorophyll product derived from SeaWiFS and MODIS/Aqua. The products are being created routinely now for daily, 8-day, monthly, seasonal and annual time periods once the refined products for each of the contributing missions are processed. The table below shows the increase in coverage over the single mission product realized through the merging of the two data sets.
% increase over SeaWiFS = 52.8617
% increase over MODIS = 60.0602
% increase over SeaWiFS = 20.5960
% increase over MODIS = 24.0016
% increase over SeaWiFS = 4.68613
% increase over MODIS = 5.10188
% increase over SeaWiFS = 0.902050
% increase over MODIS = 0.856695
As you can see, there is a substantial improvement (> 50%) in coverage at the daily level, decreasing with the increase in the temporal period binned. The Aqua/SeaWifs merged product is generated in essentially two steps. First the Aqua Level-3 file is reduced in resolution from 4 kilometer to 9 kilometer using the "reduce_fac" parameter of the L3BIN program to match the global resolution of the SeaWiFS chlorophyll product. This involved combining the sum and sum squared field values for the (typically) four 4 kilometer bins into the corresponding single 9 kilometer bin. The number of observations for the input bins are summed to give the number of observations for the output bin. In the second step, the reduced-resolution Aqua file and the corresponding Seawifs Level-3 file are combined once again using L3BIN. Because both input files are at the same 9 kilometer resolution, the summing is performed in a bin-by-bin manner. The Standard Mapped Image file that is then generated from the merged Level-3 binned file outputs a scaled 16 bit integer value rather than the usual 8 bit value, giving the user much greater numerical precision and are supported in SeaDAS. The actual images displayed on the Ocean Color website in PNG format are provided for visual inspection only and there are direct links to the 16 bit HDF files either on the Level-3 Web Browser:
or via a link on our FTP distribution page:
As always, we welcome any feedback (flowers preferred over rotten tomatoes).
Members of the Ocean Biology Processing Group