IMPROVED MODIS AEROSOL RETRIEVAL USING MODIFIED VIS/MIRSURFACE ALBEDO RATIO OVER URBAN SCENES

摘要

In this paper, we focus on the use of simultaneous MODIS and AERONET sky radiometer data to refine the surface albedo models regionally and improve on the current AOD operational retrieval. In particular, over New York City, 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 underestimated in comparison with high spatial imagery data from Hyperion thereby leading to an underestimate in the VIS ground albedos and explaining the subsequent overestimate of the VIS optical depth. Furthermore, we find that the VIS/MIR ratios depend only weakly on the scattering geometry allowing us to generate a regional VIS/MIR surface reflectance correlation coefficient map at spatial resolutions down to 1.5km. 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 10km resolution product. Moreover, we also show the high resolution surface model allows us to improve the resolution of the retrieved AOD to 3km. Although direct comparisons for a given day can only be made at the AERONET site, we find the AOD spatial variability from the improved MODIS retrievals is in far better agreement with temporal statistics seen in the AERONET time series retrievals. In addition to that, we also process and validate with another urban area, Mexico City, and the result is also significantly improved by using refined regional VIS/MIR surface reflectance ratio model.