MODIS反演多云地区地表反照率的一种新方法及其反演试验

在参考国内外卫星遥感反演地表反照率方法的基础上，提出了一种反演多云地区地表反照率的新方法，称之为组合反演法。对于受云影响而无法获得足够的晴空观测数据的像素点，在遥感地表分类数据和归一化植被指数（NDVI） 数据的辅助下，在其周围的有限范围内选择与其具有相同BRDF形状的像素点，将它们在观测角度上互为补充的晴空观测数据组合成对同一个BRDF形状的一组多角度观测数据，达到一定数量后直接利用线性的RossThick-LiSparse互易核驱动模型反演二向反射分布函数（BRDF）参数。然后，根据“16天”期间平均的当地正午太阳高度角计算反照率。选择青藏高原地区2004年6～8月间5组“16天”的Terra MODIS数据进行的反演试验表明，该方法不仅具有反演多云地区地表反照率的能力，而且能够更好地反映实际的地表信息，反演结果的精度与美国MOD43产品的精度相当。

A New Way to Retrieve Surface Albedo over Cloudy Areas with MODIS Data and the Retrieval Experiment

A new way is presented to retrieve albedo over cloudy areas,which is called compositive inversion.It selects pixels having the same BRDF(bi-directional reflectance distribution function) shape as the pixel frequently cloud-influenced within a limited area around it using information provided by data of land cover types and synchronous Normalized Difference Vegetation Index(NDVI) data,and unites their complementary angular observations into a set of multi-directional and multi-angular measurements till it is enough to retrieve reliable BRDF parameters directly with the linear kernel-driven RossThick-LiSparse Reciprocal(RossThick-LiSparseR) model.Then,black-sky albedo(BSA) and white-sky albedo(WSA) can be calculated with local noon solar altitude angle.Retrieval experiments with five "16-day" MODIS data from June to August 2004 over the Tibetan Plateau reveal that compositive inversion can retrieve albedo over cloudy areas successfully without depending on a priori BRDF information.Retrievals from compositive inversion can give more detailed land surface information than those from magnitude inversion,a method adopted in the U.S.MODIS BRDF/albedo algorithm under the same condition,and accuracy of retrievals from compositive inversion is equivalent to those from magnitude inversion.