SeaWiFS Reprocessing 2010.0

The Ocean Biology Processing Group initiated a reprocessing of the SeaWiFS dataset in September 2010. This reprocessing includes the entire mission prior to the SeaWiFS orbit raising maneuver , and was motivated in part by a desire to incorporate all calibration knowledge prior to that significant event. A second and more pressing motivation was that the lunar calibration trends of the 412-nm band (and 443-nm, to a lesser degree) have started to deviate significantly from the temporal calibration model. This drift in the lunar calibration has only become clear since the reprocessing in 2009 . The effect of this calibration drift on the derived products is most evident in trends of inherent optical properties, where the 412-nm band plays a critical role in the separation of absorption components.

The impact of this reprocessing on standard SeaWiFS ocean color products is small. Changes in the blue-green water-leaving reflectances (relative to the 2009.1 Reprocessing), at any time during the mission, are less than 3% in oligotrophic to mesotrophic waters, with slightly larger impacts in eutrophic waters. Mean changes over the mission lifespan were less than 2%. The impact to chlorophyll is less than 5% everywhere prior to 2007, and less than 1% over deep waters, with the long-term trends effectively unchanged. The largest effects occurred after 2007, due to correction of the calibration trends in the 412 and 443-nm bands.

These impacts are evident in the comparative timeseries analysis (note: st76 is R2009.1 and st81 is R2010.0). The temporal trend comparisons show overlays and ratios in different water types.

The results show a slightly larger impact to the 670-nm reflectances and the mean aerosol Angstrom retrievals, as we are also taking this opportunity to lower the threshold on aerosol reflectance below which we disable the aerosol model selection process and revert to a fixed model. This same threshold change was already made to the MODIS/Aqua processing prior to the 2009.1 reprocessing of that mission, after some artifacts were revealed in testing.

Another minor change implemented with this reprocessing was to redefine the Level-2 stray light dilation as a flag rather than a mask. This is more consistent with how we treat MODIS. We mask on this flag at Level-3, so global products are unaffected, but Level-2 data will show many more retrievals near coasts, clouds, and other bright sources. User's may rejoice, but it also increases the need for caution when using the Level-2 products. Please consider the flags.