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《Carsologica Sinica》 2011-02
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Mapping cockpit karst in Southern China from ASTER stereo images:DEM validation and accuracy assessment

LIANG FU-Yuan1,SHI Yu-ruo 2,George A.Brook3(1.Department of Geography,Western Illinois University,Macomb,IL 61455 USA;2.Beijing SHRIMP Center,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;3.Department of Geography,University of Georgia,Athens,GA 30602,USA)  
Advanced Spaceborne Thermal Emission and Reflection Radiometer(ASTER) stereo images were used to automatically produce a digital elevation model(DEM) of a rugged karst area in southern China.The accuracy of the DEM was assessed by comparing elevation data at check points and along four transects with reference data derived from 1:50 000 scale topographic maps.The quality of the DEM was significantly improved when the number of ground control points(GCPs) from the topographic maps was increased from 30 to 60 but only slightly improved when 90 points were used.The 90-point DEM had an elevation root mean square error(RMSE) of 42.7 m,which is higher than the accuracy specifications for the ASTER sensor,mainly due to the variable quality of GCPs and the rugged terrain of the study area.Topographic shadows also influenced the accuracy of the DEM,as indicated by check points in areas under shadow that had a higher RMS elevation error than those not in shadows.RMS elevation errors were also higher in areas of more rugged relief,possibly because of a larger area in shadow,and possibly also because of differences in the shadow footprint(shape and extent) on the ASTER nadir-looking and aft-looking(3n and 3b) images used to generate the DEM.Although the DEM has a slightly larger RMS error,it still provides a valuable source of topographic data for morphometric analysis of rugged cockpit karst in southern China,as the dimension of closed depressions is much bigger than the RMSE of the DEM.
【Fund】: supported by a University Research Council Grant( #3-30258) from Western Illinois University~~
【CateGory Index】: TP751;P931.5
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