Analysis And Application Of MODIS Albedos Over Tibetan Plateau

The land surface albedo is one of the important parameters as the reflection of energy balance in the earth-atmosphere system. The unique thermal and dynamic action of Tibetan Plateau affects the the weather changes in east Asia and even the whole world, such as the atmospheric circulation. Snow and glaciers are the special underlying surface of the Tibetan Plateau, and they affect each other. The high albedo of the snow and ice makes them being an important indicator of climate changes.Therefore the land surface albedo becomes the reliable datas to analyze the local and global climate changes. The characteristics of the land surface albedo can help discerning the snow and glaciers, and other land surface features. However, the ground sites over the Tibetan Plateau are relatively less and their distribution are uneven. The satellite remote sensing becomes the main means of getting the land surface albedo of the Tibetan Plateau.The MCD43 is the newly operational albedo products of MODIS (MODerate-resolution Imaging Spectroradiometer). Analyzing and validatiing the accuracy of MCD43 albedos will contribute to understand the products’quality. Similarly, analysis and validation of the relationship between albedos and snow, and using land surface albedos to monitor the changes of the glanciers are conducive to the application of albedo products over the Tibetan Plateau. Firstly, the study uses the land surface albedo results of the ground-sites over the Tibetan Plateau to validate the accuracy of MCD43B3 albedos. Secondly, this study analyzes the relation of the snow and albedos by studying IMS products and MODIS products, and lastly, the study use MCD43A3 and MOD10A1 to monitor the changes of geladandong glacier. The main conclusions are as follows.The variation trends of the ground-measured albedos are basically identical to that of MODIS albedos. In view of the spatial scale between the ground-based observation and MODIS observation, when MODIS albedos or the ground-observed albedos are less than 0.4, the root-mean-square errors (RMSEs) between the ground-based albedos and the black-sky albedos (BSA) and the white-sky albedos (WSA) derived with the full inversion and the magnitude inversion are calculated respectively. In general, the accuracy of the full inversion is higher than that of the magnitude inversion at Xidatan, Wudaoliang and Tanggula stations from 2005 to 2006. But the accuracy of the magnitude inversion is higher than that of the magnitude inversion at Amdo, BJ, D105 and NPAM from 2002 to 2004. When MODIS albedos are derived with the full inversion, the Maximum values of the RMSEs about BSA and WSA are 0.0321 and 0.0306, respectively. When MODIS albedos are derived with the magnitude inversion, the Maximum values of the RMSEs about BSA and WSA are 0.2004 and 0.2019, respectively. When the results are affected by snow, whether the accuracy of the full inversion or that of the magnitude inversion will decrease. Snow has great influnence on the accuracy of MODIS albedos.The snow area of the Tibetan Plateau is changed by seasons whether in the IMS products or in MCD43B3 albedo products. The snow area is very low every summer, and the area will significantly increase in winter. The variation trends of the snow area every year are similar. When the MCD43B3 albedo threshold is 0.3, the results about the area and the spatial distribution of the MODIS products are relatively close to the results of the IMS products. The main snow distribution area for a long time are in Pamirs, Tanggula Mountains and the Himalayas. The MODIS pixels and The IMS pixels are mutually corresponding. The MODIS pixels, which correspond to the IMS land pixels, are hardly regarded as snowy pixels, but the MODIS pixels, which correspond to the IMS snowy pixels, are easily regarded as land pixels.The monitoring results of MCD43A3 and MOD10A1 about Geladandong Glacier are similar. The concordance rates in most years are around 70%. The land surfance albedos decrease from the subject glacier to the edge in later warm seasons, and they decrease obviously by altitude. The area of the Geladandong Glacier are slowly decreasing during from 2001 to 2014. Sometimes the edge of the glacier remains relatively stable and even increase.