Preliminary Study On Retrieving Surface Albedo With FY-2D Data

Surface albedo has great impact on the radiative energy budget of the earth-atmosphere system and further affects the regional and global climate change. In the paper, data from Chinese geostationary meteorological satellite FY-2D were used to retrieve the surface albedo over China and the adjacent area. The main work of the paper is as following:(1) Atmospheric correction. After introducing the method of6S lookup table, this paper calculate the correction value of the pixel of incomplete input parameters by fitting a linear equation of reflectance before and after correction, and finally obtain accurate and continuous surface reflectance images through the revised of solar zenith angle. The results show that:the distribution of the images before and after atmospheric correction is in consistent, and the consistent correlation between them is greater than0.99. The corrected image is clearer, and can accurately show the surface features. Also, the atmospheric correction results of FY-2D have a good correlation with the MOD09CMG surface reflectance. In32cases, the correlation coefficient is greater than0.65, the maximum is more than0.9, and the correlation coefficient of the corrected is greater than that without correction. So the method in this paper is effectiveness.(2) Narrowband to broadband conversion. Take advantage of the reflectance spectra of China and the adjacent area, we use6S model to fit narrowband to broadband conversion equations of visible, near-infrared and shortwave spectra. By the contrast analysis with the MODIS broadband reflectance calculated by Liang’s conversion equations, we found the correlation coefficient is above0.8, so the conversion equation is effectiveness. Based on the confirmation of the accuracy of the method, the conversion equation of between MODIS1,2,3,4band and FY-2D visible band is obtained, which is suitable for China and the adjacent area. Comparing the MODIS broadband reflectivity calculated by the equation with FY-2D reflectivity before and after the atmospheric correction, the correlation coefficients are all above0.65in the32cases, which illustrates that the reflectivity of MODIS broadband is in good agreement with FY-2D. (3) Albedo inversion. In the paper, we will use RTLSR (RossThick-LiSparse-R) kernel driven BRDF model to retrieve white and black sky albedo of FY-2D. FY-2D and MODIS surface albedo (MCD43C3) have a good correlation, so the method is accurate. The absolute deviation between FY-2D and the MCD43C3surface albedo of some representative points, smaller absolute deviation also proves the accuracy of this method.