Retrieval of aerosol optical depth using FY-3D MERSI-II data over land

Abstract

<p>Fengyun 3 (FY-3) series of satellites is the second generation of Chinese polar-orbit, sun-synchronous meteorological satellites. As the fourth satellite in the series, FY-3D carries 10 sets of remote-sensing instruments to observe the earth's atmosphere, biosphere, hydrosphere, and cryosphere. The Medium Resolution Spectral Imager-II (MERSI-II) onboard the FY-3D satellite is equipped with aerosol-associated bands similar to MODIS which has great capability in detecting aerosols. However, there is still a lack of a stable and reliable aerosol retrieval method for the operational inversion of aerosols from MERSI-II images. This study focuses on developing a high-precision algorithm to retrieve aerosol optical depth (AOD) over entire land areas (except snow/ice and inland waters) based on MERSI-II observations. A new cost function was constructed to improve the retrieval efficiency based on the spectral dependence of AOD and the slow spatial variation of aerosol types. To extend the application adaption of the FY-3D MERSI-II AOD retrieval and avoid the errors caused by the surface Lambertian hypothesis, a monthly bidirectional reflectance distribution function (BRDF) database is built using Moderate Resolution Imaging Spectroradiometer (MODIS) products. Eight candidate aerosol optical models in different natural zones of China are constructed based on long time series of AERONET aerosol products. The new method is applied to MERSI-II images over China and validated with ground-based measurements from 14 stations in 2021. MODIS aerosol products from dark target (DT), deep blue (DB), and Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithms are also used for comparison purposes. The results show that MERSI-II AOD retrievals agree well with the ground-based measurements with correlation coefficient (R) and root mean square error (RMSE) of 0.911 and 0.128, respectively. In addition, 70.91% of AOD matchups fall within the expected error envelopes (± (0.05+20%)). MERSI-II AOD also shows higher stability in terms of spatial and temporal and better performance under heavy aerosol loading conditions than MODIS products. A good agreement in AOD distribution is also shown between MERSI-II and MODIS products with R of 0.756 to 0.868.</p>