Comparison of an Aerosol Assimilation System of MODIS Radiances with AERONET retrievals.

We present results from a simple off-line assimilation system of radiances from the MODIS channels that sense atmospheric aerosols over land and ocean. The MODIS information is directly inserted into the Goddard Chemistry and Aerosol Radiation Transport Model (GOCART) which simulates five aerosol types: dust, sea salt, black carbon, organic carbon and sulfate. We compare the products from this assimilation system with ground-based measurements of aerosol optical depth (AOD) and single scattering albedo from the AERONET network. Insertion of MODIS radiances draws the GOCART model closer to the AERONET AOD. Over ocean the assimilation aerosol optical depths (AOD) compare well with AERONET, over land less so. However, there are still uncertainties with surface reflectivity and the amount of absorbing aerosol when we assimilate using only the seven MODIS aerosol channels (.47 to 2.13 um). We will present new results using an additional channel at .412 um that should resolve some of these issues. We account for the effect of chlorophyll absorption on the water leaving radiance by using concentrations from a three-dimensional ocean general circulation biogeochemical model. Inclusion of the chlorophyll reduces the O-F radiances at the shorter wavelength MODIS channels.