MODIS卫星数据地表反照率反演的简化模式

以内蒙西部地区的MODIS遥感图像数据和地表野外同步观测的光谱数据为例,在野外数据量较少且有定标数据的条件下反演地表反照率。使用6S大气1辐射传输模型进行大气校正,并通过MODTRAN4.0模型获取各波段地表入射光通量和窄波段的地表反照率;在窄波段反照率与宽波段反照率之间存在线性关系的前提下,以各波段的入射光通量占总入射通量的比例作为反演参数,实现窄波段到宽波段的反演。反演结果证明此方法简便可行。

A Simplified Surface Albedo Inverse Model with MODIS Data

Land surface albedo, which is a fundamental component needed for determining the radiation balance of the Earth-atmosphere system, is the surface hemispherical reflectivity integrated over the solar spectrum. Briefly said, it is the ratio of the total upwelling irradiance to the total downward irradiance. Given the limit of experiment field and instrument equipment, it is very difficult to obtain a great deal of surface measured data. Thereof, in our research, from the point of view that surface albedos are the ratio of flux, surface albedos can be reversed with less calibrated field synchronous observed data. During the conversion process of surface albdeos, the first is to obtain surface reflectance from remotely sensed data, which can be completed by running 6S atmospheric radiative transfer model; the second is to reverse surface narrowband albedos, which is fulfilled by MODTRAN model. The outputs of MODTRAN simulations are upwelling and downwelling irradiance. The sensor spectral response functions are integrated with these outputs to generate narrowband albedos; the third is to calculate surface broadband albedos, which is focused on determining the converting coefficients from narrowbands to broadbands under the the linear relationship between narrowband albedos and broadband albedos. The spectral distribution of solar irradiance at the surface is set as the weighting function for comverting the narrowband albedos to broadband albedos in the research. The conversion of broadband albedos is fulfilled finally. The simplified surface broadband albedo reverse model is tested for the west of Inner Mongolia using MODIS image data and synchronous observed surface spectral data based on the above conversion algorithm. The results show that the method is convenient and feasible under a specific surface/atmospheric condition.