Aerosol and surface products from cross-track scanning polarimeter POSP onboard GF-5(02) satellite (December 2021 - May 2023)

The Particulate Observing Scanning Polarimeter (POSP) onboard the GF-5(02) satellite, as part of the Polarization Cross-Fire (PCF) observation system, provides critical data for atmospheric aerosol and surface studies. This dataset contains aerosol and surface products collected by POSP from December 2021 to May 2023. Using high-precision multi-spectral (UV-VIS-NIR-SWIR) polarimetric observations, POSP provides valuable information on aerosol and surface characteristics. The dataset is generated using the Generalized Retrieval of Atmosphere and Surface Properties (GRASP) framework, a mature method for retrieving aerosol and surface reflectance from polarimetric data. POSP delivers detailed aerosol parameters such as Aerosol Optical Depth (AOD), fine-mode (AODF) and coarse-mode (AODC) optical depths, Ångström Exponent (AE), Single Scattering Albedo (SSA), and aerosol scale height. These products are essential for understanding aerosol size distribution, absorption, and layer height, which are important for studying climate and air quality impacts.Additionally, the dataset includes surface products such as the Bidirectional Reflectance Distribution Function (BRDF), Bidirectional Polarization Distribution Function (BPDF), black-sky and white-sky albedos, and the Normalized Difference Vegetation Index (NDVI). These variables are crucial for monitoring surface properties and assessing changes in surface reflectance and vegetation. Validation of the POSP aerosol products against AERONET reference data shows a good agreement, with correlation coefficients for AOD (550 nm) ranging from 0.82 to 0.87 over land and ocean, and RMSE within 0.12 over land and 0.09 over the ocean. The data is provided in NetCDF format, which facilitates integration with climate models and geospatial analysis tools, and is suitable for climate modeling, environmental monitoring, and Earth system science research.Product specification: List of fields in the POSP/GF-5(02) Level 2 NetCDF fileCriteria to select high-quality retrievals(i)            The relative fitting residual (residual_relative_noise0) smaller than 5%;(ii)           Over land, the AOD (865 nm) standard deviation within its 3x3 window (STD_AOD865) smaller than 0.1 or STD_AOD865 / Mean(AOD865) smaller than 0.2, where Mean(AOD865) is the mean AOD with the 3x3 window. Over ocean, the STD_AOD865 is smaller than 0.05;(iii)          The number of valid retrievals with a 3x3 window need to be higher or equal to 3.Know IssuesDuring the first POSP/GF-5(02) processing, we also identify some remain issues in the current baseline Level 2 products. (i) The cloud and glint mask over ocean seems too strict resulting in the ocean pixels percentage is much lower than expected; (ii) We also identify some existing stripes in the Level 2 aerosol and surface products that are caused by the delay of Level 1 data production, therefore some Level 1 tracks are recorded until the next day and overwrite the coming data. These known issues are documented in the data description and expected to be solved in the next processing. The orbit information with potential overlapping is provided together with the product files.Other unknowns …For more details about the processing method and data evaluation, please refer to the manuscript:https://essd.copernicus.org/preprints/essd-2024-483/