Integration of radiative transfer into satellite models of ocean primary production

A major goal of ocean color observations from space is the determination of phytoplankton primary productivity (PP) and hence oceanic carbon uptake. Results of a PP model implemented to use satellite-derived fields of chlorophyll, photosynthetically available radiation (PAR) and sea-surface temperature (SST) are presented. The model gave a global estimate of PP of around 57 Gt C yr(-1) and gives a low RMS (0.16) when compared with in situ data. However, as the model's in-water light field parameterization only considers attenuation by pure water and chlorophyll, PP is overestimated in case II waters where other optically important constituents such as colored dissolved organic matter (CDOM) and suspended particulate matter (SPM) are also present. This paper develops a novel technique to determine PP by coupling a radiative transfer code, which allows the inclusion of CDOM and SPM, to the original photosynthesis model. For the global calculations, a look-up table has been generated using chlorophyll, CDOM, SST, PAR and day length as inputs. The resultant 364,500 element look-up table has been applied to data from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and Moderate-Resolution Imaging Spectroradiometer (MODIS). PP retrievals are improved in case II waters and global estimates are reduced to between 52 and 55 Gt C yr(-1).