Inversion Of Surface Reflectance In Ragged Area Based On MODIS Data

In the mountainous area with undulating terrain,the surface information recorded by the optical satellite sensor is affected by the terrain and there is a certain difference between the real information of the ground objects.This difference can be eliminated by terrain correction.The purpose of terrain correction is to correct the difference in the incident solar irradiance caused by slope and aspect,and to restore true surface information.This paper considers the effect of the surrounding terrain,deduces the undulating surface reflectance model,and inverts the undulating surface reflectance.Based on the theory of radiation transmission,the radiation received by the earth's surface is divided into solar direct radiation,atmospheric scattered radiation,and surrounding terrain reflected radiation.Direction-direction reflection and direction-hemispherical reflection were introduced,and the surface relief model was obtained based on the relationship of irradiance,radiance and reflectance.In combination with RTLSR model and Hapke model,the undulating surface reflectance model based on RTLSR and the undulating surface reflectance model based on Hapke are obtained.Using the MODIS 09 reflectance data and ASTER GDEM data combined with the undulating surface reflectance model to perform inversion of surface reflectivity in the area south of Ruoqiang Town,Ruoqiang County,Bayingolin Mongolian Autonomous Prefecture,Xinjiang Uygur Autonomous Region.In the relief surface topographic factor solution,reflectance information is extracted from MOD09GQ/MYD09 GQ data.Solar zenith angle,solar azimuth,observation of the zenith angle and observation of the azimuth angle are extracted from MOD09GA/MYD09 GA data.The slope and aspect,terrain-view factor,sky-view factor were calculated from the data of ASTER GDEM.The direct irradiance of the sun and the irradiance of the atmospheric scattering were obtained by MODTRAN.Inversion of the undulating surface reflectivity model factor based on RTLSR and the undulating surface reflectance model factor based on Hapke are compared with RTLSR model factor and Hapke model factor,respectively.The results show that the model factor difference increases with the increase of slope,and it is necessary to apply the undulating surface reflectance model in the study of remote sensing parameter inversion.Inverting the surface reflectance of the undulations and evaluate the inversion results.The MODIS image reflectance,Cosine model corrected MODIS reflectance,and C model corrected MODIS reflectance were compared.The comparison results show that the Hapke model is suitable for the low reflectivity region inversion study,and the inversion error is larger in regions with reflectance higher than 0.3.The RTLSR-based undulating surface reflectance model works best for inversion of reflectivity.