National Civil Space Infrastructure Satellite Aerosol Product Validation Network (SIAVNET) measurements: Supporting satellite aerosol product validation for different surface types over China

Understanding the uncertainty of satellite aerosol products for different surface types is very important for algorithm optimization and related applications. Ground-based aerosol observations provided by AERONET are most often used to validate satellite aerosol products. However, AERONET ground-based sites are unevenly distributed in China, mainly concentrated in urban areas, with few sites in other surface types, leading to limitations in evaluating the accuracy of products for different surface types. To address this issue, the National Civil Space Infrastructure Satellite Aerosol Product Validation Network (SIAVNET) is constructed to complement ground-based aerosol observations for multiple surface types in China and support the validation research of satellite aerosol products. The main purpose of this paper is to introduce SIAVNET and analyze the supplementary role it plays in the validation of satellite aerosol products for different surface types in China. Firstly, this study introduces the supplementation of SIAVNET to ground-based observations in different surface types. SIAVNET supplements 21 sites with multiple surface types, mainly supplementing vegetated areas, with 17 sites. In particular, SIAVNET places a site in bare land, which fills the gap of ground-based observation for bare land. Then, to further demonstrate the supplemental value of SIAVNET observation in the validation of satellite aerosol products, the accuracy of MODIS aerosol products with four different resolutions (i.e., 1 km, 3 km, 10 km, and 1°) for different surface types in China is evaluated using all ground-based observations. For bare land, the accuracy of different resolution products is obtained based on SIAVNET observations, with 50.91%–69.23% of the retrievals falling within the expected error, which fills the validation gap for bare land. For vegetated areas, compared to the AERONET-only based products evaluation, the use of SIAVNET significantly affects the validation results in grassland for the 3 km and 10 km products, with the proportion of retrievals falling within the expected error decreasing from 78.61%, 74.30% to 64.16% and 63.17%, failing to reach satisfactory levels (66%). For urban areas, supplemental SIAVNET observations have almost no effect on the validation results for the different aerosol products obtained based on AERONET. These results are expected to provide guidance for detailed satellite aerosol product validation over China using SIAVNET data.