SeaWiFS Ocean Reprocessing 5.1

The primary purpose of SeaWiFS reprocessing 5.1 is to update the K_490 and chlorophyll products. The K_490 update was approved by consensus at the OCRT meeting in April. The chlorophyll change is due to an update of the solar spectrum model to Thuillier 2003. At the same time, we have decided to update the ancillary ozone archive to incorporate the recently reprocessed TOMS Version 8 data. The TOMS project started producing Version 8 products in August of 2004, and our existing ancillary archive reflects that shift, but we are now updating the historical archive from TOMS Version 7 to TOMS Version 8. This is expected to have a small impact to water-leaving radiance retrievals, especially in the 555nm channel, but we have not yet evaluated this effect. Finally, it has been suggested by users that we change the dimensions of the 9-km SMI map products from 4096x2048 to 4320x2160, to better match the latitudinal distribution of the input Level-3 bin files and thereby reduce sampling bias in the map products. Details of these changes are provided below, along with test results to indicate the impact of the changes.

The K_490 and chlorophyll changes discussed here were put into forward-stream production in May 2005. Reprocessing of the mission archive was completed in July 2005.

Status of Current Operational Products

The current SeaWiFS operational products are based on reprocessing 5.

Proposed Changes

  • Updated K490
  • Thuillier-based Rrs
  • Switch to TOMS V8 Ozone
  • Revised dimension of 9km SMI maps
  • Evaluation of Reprocessing Configuration

    Prior to the ozone update, a complete mission reprocessing was performed on a temporal subset consisting of the first 4 days of each 32-day period to evaluate the K_490 and solar irradiance updates. A generic discussion of the analysis methods is available here. On average, the change from Neckel & Labs to Thuillier solar irradiances has the effect of raising OC3 chlorophyll by 3% in clear water and 5% in coastal waters, but larger changes are possible. No change in nLw was expected or observed. The effect of the solar irradiance change relative to SeaWiFS reprocessing 1.1 on global deep-water nLw and chlorophyll is shown below. The complete analysis is available here.

    The ozone update has the effect of generally reducing the normalized water-leaving radiances at 555nm, which also impacts the chlorophyll. The effect of the ozone change to global mean chlorophyll is usually in the opposite direction to that of the solar irradiance change. As a result, the change in global mean chlorophyll (e.g., deep-water average) due to this reprocessing can be negligibly small for some periods, but changes on a regional spatial scale can still be significant. The cumulative effect relative to SeaWiFS reprocessing 1.1 on global deep-water nLw and chlorophyll is shown below.

    For further details, see: