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The Applicability of MODIS Land Surface Temperature Products to Simulating the Permafrost Distribution over the Tibetan Plateau

WANG Zhi-xia1,NAN Zhuo-tong2,ZHAO Lin2(1.College of Earth & Environmental Sciences,Lanzhou University,Lanzhou Gansu730000,China; 2.Cold and Arid Regions Environmental and Engineering Research Institute,Chinese Academy of Sciences,Lanzhou Gansu 730000,China)  
As a main parameter of energy balance on the earth surface,the land surface temperature(LST) is one of the necessary boundary conditions of a numerical permafrost model,and it is also an important observational item of any permafrost monitoring.Traditionally land surface temperature data are collected from meteorological stations.However,the point observation often cannot represent an areal situation well especially in mountainous areas.With its development,the remote sensing technique increasingly becomes an applicable way to observe land surface temperature.The limitations here are generally caused by complex terrain conditions which consequently bring large uncertainties to the derivation of LST.Applicability analysis is required prior to formal application of the derived LST data.This paper will investigate the applicability of MODIS LST products to permafrost simulation over the Tibetan Plateau,through single-point,area,and model based analyses.The single-point analysis,which compares 0-cm temperature data from 69 meteorological stations over the plateau to the MODIS LSTs of the corresponding grid cells,shows the MODIS LSTs have similar trends as measured 0-cm temperature data,but with obvious difference in terms of magnitude.The areal analysis,comparing the time series MODIS LST data to two interpolated areal 0-cm temperature data sets derived respectively by a LAT/LON/ELEV regression approach and a Kriging interpolation,reveals that there are a fairly good consistency between MODIS LST and regressed data set in terms of both space and time regardless of some differences.Meanwhile poor agreement is found between MODIS LST and Kriging interpolated data set as shown a small correlation and large mean differences.Both the single-point and areal analyses present poor agreements in the warm seasons(May-August) than the cold seasons(September-April).For model validation,the semi-physical and semi-empirical TTOP model were chosen,and the measured temperature data and the MODIS LST products were used,respectively,to simulate the permafrost distribution on the Tibetan Plateau.Area statistics and Kappa agreements calculated from the model approach show that the simulation with MODIS LST is closer to the published permafrost map.
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