MISR和MODIS二向性反射数据产品的对比分析

Comparison of MISR and MODIS bidirectional reflectance products

利用4种地表类型共16个地面站点的MISR9个角度反射率数据产品和MODIS反射率数据产品(MOD09A1),对比两种传感器获取的地表方向反射观测数据和用BRDF模型参数产品计算的方向反射数据,分析了这两种BRDF模型参数的外推能力。研究结果表明:(1)MISR和MODIS BRDF模型参数数据产品都具有一定的对观测数据以外方向反射的外推能力,相比用MISR BRDF模型参数数据外推到相应MODIS观测角度方向反射的结果一致性较强。(2)采用两种BRDF模型参数推算的方向反射率与观测数据的接近程度有随观测天顶角的增大而减弱的趋势,在观测天顶角较小时一致性较好。(3)所用数据处理结果显示,MODIS BRDF模型参数数据产品在近垂直主平面方向反射率推算结果相比近主平面方向的推算结果更接近观测数据。

The Bidirectional Reflectance Distribution Function （BRDF） of land surfaces specifies the behavior of surface directional reflectance as a function of illumination and viewing angles. The bidirectional reflectance products of the Moderate resolution Imaging Spectroradiometer （MODIS） and the Multiangle Imaging Spectroradiometer （MISR） and their BRDF model parameters products have been available respectively. Since the BRDF model parameters are inverted from limited angular observations for a given pixel, it is necessary to evaluate whether they can effectively characterize the directional reflectance in other viewing directions. In this study, we choose four kinds of land cover types to analyze the representation of MISR and MODIS BRDF model parameters, by comparing the directional reflectance extrapolated using the BRDF model parameters with the observed directional reflectance. The results show that： （1） both MODIS and MISR BRDF model parameters have better representation on directional reflectance at some viewing directions. Especially MISR BRDF model parameters have preferable representations at MODIS viewing directions; （2） the representative ability of both BRDF model parameters tends to weaken when the viewing zenith angle increases; （3） from the analysis of the observed data set shown in this paper, it seems that the representative ability of MODIS BRDF models is better near cross-principal plane than that near principal plane.