Aerosol Optical Depth Retrieval on Particulate Observing Scanning Polarimeter (POSP) Data over Land using a new Look-up table (LUT) Search Method

Abstract Accurate estimation of Land Surface Reflectance (LSR) is the key to Aerosol Optical Depth (AOD) retrievals. However, it is noted that the band-specific LSRs retrieved using Look-Up Tables (LUTs) are typically pseudo-LSRs obtained by atmospheric corrections to the AOD predetermined in the LUTs that do not match the surface constraints established by the true LSRs alone. As a result, there is an uncertain error in modeling reflectance at the top of atmosphere (TOA) using pseudo-LSRs calculated by linear interpolation. This study proposed a new LUT search method to improve the AOD retrievals of the Particle Observing Scanning Polarimetry (POSP) sensor onboard the China GaoFen-5 (02) satellite. LSR atmospherically corrected using ERA5 reanalysis data and POSP AOD products for the year 2022 was adopted to create a new full-spectrum LSR self-consistent surface constraint. Results showed that the AOD of POSP in January 2023 retrieved using the new method agrees with the ground-truth AOD values from AErosol RObotic NETwork (AERONET) site observations with the correlation coefficient (R) at 0.703 and the root mean square error (RMSE) at 0.068. 76.77% of the values fell into the expected error (EE) envelope of range ± (0.05 + 0.15 AODAERONET), and 67.35% met the accuracy requirements of the Global Climate Observing System (GCOS).