Improved MODIS Aerosol Retrieval using Modified VIS/MIR Surface Albedo Ratio over Urban Scenes

In this paper, we focus on the use of simultaneous MODIS and AERONET sky radiometer data to regionally refine the MODIS surface albedo models which are used for the AOD retrieval over land and improve on the current operational retrieval. In particular, we show that the correlation coefficient assumption used in the MODIS Collection (5) model between the VIS and MIR channels used for surface reflection parameterization are still severely optical depth. When applying the new VIS/MIR surface reflectance ratio model, we show the MODIS and AERONET derived optical thickness agreement is significantly improved for the operational 10 km resolution product. Furthermore, we show the high resolution surface model allows us to improve the resolution of the retrieved AOD to 1.5 km. We find the AOD spatial variability from the improved MODIS retrievals is in far better underestimated in an urban area in comparison with high spatial resolution imagery data from Hyperion thereby leading to an underestimate in the VIS ground albedos and explaining the subsequent overestimation of the VIS aerosol.