Estimation of optical parameters of sand dust clouds and ground reflectance from satellite data

The yellow sand dust transported from desert areas in the northern part of China is regarded as a main source of atmospheric aerosols in East Asia. A new method for estimating optical parameters of dust clouds and the surface reflectance simultaneously from POLDER data is described. The radiance and polarization at the top of the atmosphere were computed as a function of the optical thickness of dust clouds at 550 nm, t(550), refractive index of dust particles, Nr, exponent of Junge power-law, a, and the surface reflectance, A, and their values were saved in a look-up table, LUT. Optical parameters of dust clouds and the surface reflectance were determined such that the sum of relative absolute errors between the observed reflectance and polarization and those obtained from the LUT is minimum. Optical parameters of the dust cloud over a desert area and the surface reflectance were estimated at each of 443 nm and 670 nm channels. As a result, it is found that the values of parameters estimated at the 443 nm channel are almost the same as those at the 670 nm channel except for t(550).