Prior information supported aerosol optical depth retrieval using FY2D data

The algorithm is based on the assumption that TOA reflectance increase with the aerosol load as well as the surface reflectance at same time gradually changes on different days within 14 days. Then the surface reflectance is derived from FengYun-2D (FY2D) measurements every 1 hour as the second darkest of reflectance for each time of day to minimize the effect of geometry change and cloud. The "true surface reflectance" of each time was calculated from the composite reflectance and their weighs. The weigh of each time, contribution of the surface and aerosol background were determined using the prior information, and both of them were various in different time. The AOD retrieval based on a Look-Up Table (LUT) using composite background (CB) method and improved composite background (ICB) algorithm were compared with AERONET sites, it was found that the ICB provides larger coverage and higher accuracy AOD product compared with CB.