A generalized land surface reflectance reconstruction method for aerosol retrieval: Application to the Particulate Observing Scanning Polarimeter (POSP) onboard GaoFen-5 (02) satellite

Newly launched sensors often face challenges in obtaining sufficient observations in a short time to support the development of land surface reflectance (LSR) constraint for high-precision aerosol retrieval. To address this problem, we proposed a generalized spectral LSR reconstruction method. First, short-term overlapping observation of the target sensor and a reference sensor currently in operation is utilized to generate a representative spectral LSR comparison dataset. Then, the differences in spectral LSR caused by spectral response functions (SRF) are explored to construct a spectral LSR reconstruction model, which can convert the reference sensor's spectral LSR to match the spectral LSR of the target sensor. Finally, long-term spectral LSR data of the reference sensor can be reconstructed for the target sensor to support the surface constraint for aerosol retrieval. We applied this method to the newly launched Particulate Observing Scanning Polarimeter (POSP) instrument onboard GaoFen-5 (02) satellite, using MODIS as the reference sensor. We used one-month concurrently overlapping observation of POSP and MODIS to quantify the differences in spectral LSR and built the spectral LSR reconstruction model. Four years of MODIS LSR data were then reconstructed to develop the multispectral surface constraint scheme (B2RE) for POSP, which enables POSP data for high-precision AOD retrieval. We retrieved the global AOD at 550 nm over land for December 2021 to February 2022. Validation results of POSP AOD against AErosol RObotic NETwork (AERONET) AOD show that the POSP AOD derived from 490 nm observation is the most accurate with the correlation coefficient (R) of 0.914, root mean square error (RMSE) of 0.080, mean relative error (MRE) of 1.60% and 82.5% of the values falling into the expected error (EE) envelope of & PLUSMN; (0.05 + 0.15AODAERONET). The spatial distribution of monthly POSP AOD also has good agreement with MODIS Deep Blue AOD product.