Development of level 2 aerosol and surface products from cross-track scanning polarimeter POSP onboard GF-5(02) satellite

Abstract. Development of long-term continues, consistent and high-quality satellite remote sensing aerosol and surface products is crucial to constrain climate models and improve our understanding on climate change. Particulate Observing Scanning Polarization (POSP) is the first space-borne multi-spectral (UV-VIS-NIR-SWIR) cross-track scanning polarimeter dedicated to complement Directional Polarimetric Camera (DPC) multi-angular polarimetric measurements and perform synergetic observations namely the Polarization Cross-Fire suite (PCF) onboard Chinese Gaofen series GF-5(02) satellite. The POSP unique single-viewing spectral (UV-VIS-NIR-SWIR) high-precision polarimetric measurements provide rich information for atmospheric aerosol and surface characterization. Here we developed aerosol and surface products from POSP/GF-5(02) based on the Generalized Retrieval of Atmosphere and Surface Properties (GRASP)/Models approach. The detailed retrieval approach and processing scheme are provided. The baseline level 2 product was generated for the first 18 months POSP measurements from December 2021 to May 2023 and publicly available and registered at doi.org/10.57760/sciencedb.14748. The obtained POSP/GF-5(02) aerosol and surface products are validated and intercompared with ground-based AERONET reference aerosol dataset and other independent satellite products, such as NOAA-20 VIIRS/DB aerosol product and MODIS MCD43 surface product. The results show generally good consistency of POSP products with AERONET, VIIRS/NOAA-20 aerosol dataset and MODIS surface product. Moreover, it is possible to conclude the developed POSP product includes reliable estimates of not only total Aerosol Optical Depth (AOD), but also detailed properties of aerosol such as aerosol size, absorption, layer height, type, etc., as well as full surface Bidirectional Reflectance Distribution Function (BRDF), Bidirectional Polarization Distribution Function (BPDF), and black-sky, white-sky albedos and Normalized Difference Vegetation Index (NDVI). These parameters are of high importance to constrain the Earth-atmosphere radiation budget. The retrieval of these properties seems to be possible due to the polarimetric capabilities and wide UV-VIS-NIR-SWIR spectral range of from POSP observations and advances of used GRASP/Models retrieval approach. Finally, some potential improvements for POSP level 1 to level 2 processing chain are identified, and limitations and lessons learned are discussed.