MODIS、MISR与POLDER 3种全球地表反照率卫星反演产品的比较与分析

对MODIS、MISR和POLDER 3种由多角度卫星观测反演得到的全球地表反照率数据(无冰雪覆盖区域)短波波段(SW,0.3~5 μm)与可见光波段(VIS,0.3~0.7 μm)的黑空地表反照率(DHR)进行了相互比较。3种产品6年平均的全球均值存在显著差异,其值从大到小依次为POLDER,MISR和MODIS。3种产品的纬向平均在35°N以北区域表现出较大的差异。3种产品彼此之间相关性比较高,其中MODIS与MISR产品的相关性最强,MISR与POLDER产品的相关性最低,短波波段的相关系数(r) 分别为0.939与0.911。3种产品在可见光波段的相关性大于短波波段。在不同地表类型上,3种产品表现出了大致相似的差异,表明其对地表类型并不敏感。对气溶胶的分析表明:MODIS与MISR的550 nm气溶胶光学厚度(AOD)较为相似,其差异不足以解释DHR的差别;但是POLDER的865 nm AOD明显小于MISR,因此可以认为是由于POLDER的AOD估算偏低,导致了POLDER的DHR值大于MODIS与MISR。

Intercomparison of Albedo Product Retrieved from MODIS,MISR and POLDER

Albedo is a key parameter of climate model.Global albedo products retrieved from Multi|angular satellites has been used in Climate modeling investigation.But the consistencies among these albedo products have not been sufficiently analyzed.So this paper compared the Level|3 directional|hemispherical reflectance (DHR) products (snow|free area only) retrieved from MODIS,MISR and POLDER.Two broadband DHR were used,namely,shortwave (DHR_SW,300~5 000 nm) and visible (DHR_VIS,300~700 nm).The results revel that six|year average of these products shows an evident relationship of POLDER>MISR>MODIS.There are systematic differences among these products.The differences on global means of DHR_SW (DHR_VIS) are 0.01~0.02(0.01~0.03) for MODIS and MISR,0.02~0.05(0.03~0.07) for MODIS and POLDER,and 0.01~0.03(0.01~0.04) for MISR and POLDER,respectively.Differences are larger in visible band than shortwave band.The zonal means of the three products show relative large differences in latitudes higher than 35°N,which may accumulate snow in winter and snow|melt in spring.The correlations among the three products are high,in which MODIS and MISR is the highest,MISR and POLDER is the lowest,the correlation coefficients in shortwave band are 0.939 and 0.911,respectively.Although the difference between MODIS and POLDER is the largest,their correlation is still high,e.g.0.937 in shortwave.The correlations are higher in visible than in shortwave.The differences are almost similar to all land cover types,which shows it is not sensitive to the land cover type.The differences in Aerosol Optical Depth(AOD) between MISR and POLDER may contribute to the corresponding discrepancy in DHR,but cannot explain the differences between MISR and MODIS.Although the three products utilized different retrieve algorithm,they showed good correlation,the main discrepancy may come from the atmospheric correction process,which shows that their albedo retrieval algorithm are practicable.