An improved method for retrieving aerosol optical depth over Ebinur Lake Basin from Gaofen-1

Abstract

Lake Ebinur is the largest saltwater lake in Xinjiang. In recent years, the exposed dry lake bottom surface has become a remarkable source of salt and dust owing to the desiccation of the lake. Given the importance of the lake basin to human livelihoods, comprehensive monitoring of basin behavior is required. Remote sensing offers numerous novel approaches to monitoring the spatial and temporal distribution of aerosols. During this study, high spatial resolution aerosol optical depth (AOD) inversion at Lake Ebinur was still in the gap stage. The wide-field-of-view (WFV) data from four cameras on the GaoFen-1 (GF-1) satellite, launched by China in April 2013, offers high spatial and temporal resolution and excellent potential for AOD estimation. Owing to the shortwave infrared band (SWIR) deficiency and the complexity of surface reflectance, the coefficient of variation (CV) was proposed as a measure of surface reflectance to develop a surface reflectance database for land cover characteristics in the Ebinur Lake Basin. The significant improvements of the algorithm include (1) the design of an accurate and universal cloud detection algorithm through the blue and red bands. (2) The CV was used to assess the robustness of surface reflectance under long time series. After dividing the surface reflectance image pixels with low robustness, a reasonable value was assigned according to the surface reflectance variation characteristics of the image pixels. (3) Aerosol models were determined from the long-term measurements of the CIMEL solar photometer (CE318), and the validation of ground-based observations showed good correlation that WFV/GF-1 AOD was comparable to CE318 AOD (R = 0.705; root mean square error (RMSE) = 0.098; mean absolute error (MAE) = 0.078), and the smaller MAE and RMSE confirmed the feasibility of inversion of AOD by this method.