Modeling Land Surface Reflectance Coupled BRDF for HJ-1/CCD Data of Rugged Terrain in Heihe River Basin, China

Rugged terrain significantly affects the Huan Jing (HJ)-1/CCD reflectance at the earth´s surface because the sloping surfaces change the sun-surface-sensor geometry. It is necessary to consider the land surface directional reflectance and reduce topographic effects to obtain the correct reflectance. An atmospheric model 6S (second simulation of the satellite signal in the solar spectrum) coupled with bidirectional reflectance distribution function (BRDF) shape, which is well suited to estimate the HJ-1/CCD land surface reflectance of rugged terrain and flat surface (BRATC, BRDF-based atmospheric and topographic correction), is reformulated in this paper. The BRDF shape, a statistics-based MODIS (moderate-resolution imaging spectroradiometer) BRDF prior-knowledge look-up table (LUT) stored in this algorithm, is applied to the HJ-1/CCD reflectance estimation that covers Heihe River Basin, China. The results of the indirect validation of the visual image and the linear relationship between the reflectance and the cosine of the solar relative incident angle show that the algorithm effectively reduces topographic effects. Compared with three land cover field measurement reflectances, the HJ-1/CCD-corrected reflectance is consistently good with an overall RMSE as low as 0.0128. The proposed method could be designed for an operational system of HJ-1/CCD reflectance products.