Digital Elevation Models(DEMs)contain topographic relief data that are vital for many geoscience applications.This study relies on the vertical accuracy of publicly available latest high-resolution(30 m)global DEMs ov...Digital Elevation Models(DEMs)contain topographic relief data that are vital for many geoscience applications.This study relies on the vertical accuracy of publicly available latest high-resolution(30 m)global DEMs over Cameroon.These models are(1)the ALOS World 3D-30 m(AW3D30),(2)the Shuttle Radar Topography Mission 1 Arc-Second CBand Global DEM(SRTM 1)and(3)the Advanced Spaceborne Thermal Emission and Reflection Global DEM Version 2(ASTER GDEM 2).After matching their coordinate systems and datums,the horizontal positional accuracy evaluation was carried out and it shows that geolocation errors significantly influence the vertical accuracy of global DEMs.After this,the three models are compared among them,in order to access random and systematic effects in the elevation data each of them contains.Further,heights from 555 GPS/leveling points distributed all over Cameroon are compared to each DEM,for their vertical accuracy determination.Traditional and robust statistical measures,normality test,outlier detection and removal were used to describe the vertical quality of the DEMs.The test of the normality rejected the hypothesis of normal distribution for all tested global DEMs.Overall vertical accuracies obtained for the three models after georeferencing and gross error removal in terms of Root Mean Square(RMS)and Normalized Median Absolute Deviation(NMAD)are:AW3D30(13.06 m and 7.75 m),SRTM 1(13.25 m and 7.41 m)and ASTER GDEM 2(18.87 m and 13.30 m).Other accuracy measures(MED,68.3% quantile,95% quantile)supply some evidence of the good quality of AW3D30 over Cameroon.Further,the effect of land cover and slope on DEM vertical accuracy was also analyzed.All models have proved to be worse in the areas dominated by forests and shrubs areas.SRTM 1 and AW3D30 are more resilient to the effects of the scattering objects respectively in forests and cultivated areas.The dependency of DEMs accuracy on the terrain roughness is evident.In all slope intervals,AW3D30 is performing better than SRTM 1 and ASTER GDEM 2 over Cameroon.AW3D30 is more representative of the external topography over Cameroon in comparison with two others datasets and SRTM 1 can be a serious alternative to AW3D30 for a range of DEM applications in Cameroon.展开更多
A broad view of present-day 3D deformation field around the Northeast China region was derived from GPS and leveling observations. We draw the following conclusions： First, the Northeast China region moved towards no...A broad view of present-day 3D deformation field around the Northeast China region was derived from GPS and leveling observations. We draw the following conclusions： First, the Northeast China region moved towards northwest with an average velocity of 5 ram/a, with respect to South China. The entire Northeast China region was in a low strain state from the strain rate field. Second, we processed two periods of first- order leveling data in 1970s and 1990s, showing the vertical deformation of the Northeast China region is ＂uplift in western part and subsidence in eastern part＇展开更多
文摘Digital Elevation Models(DEMs)contain topographic relief data that are vital for many geoscience applications.This study relies on the vertical accuracy of publicly available latest high-resolution(30 m)global DEMs over Cameroon.These models are(1)the ALOS World 3D-30 m(AW3D30),(2)the Shuttle Radar Topography Mission 1 Arc-Second CBand Global DEM(SRTM 1)and(3)the Advanced Spaceborne Thermal Emission and Reflection Global DEM Version 2(ASTER GDEM 2).After matching their coordinate systems and datums,the horizontal positional accuracy evaluation was carried out and it shows that geolocation errors significantly influence the vertical accuracy of global DEMs.After this,the three models are compared among them,in order to access random and systematic effects in the elevation data each of them contains.Further,heights from 555 GPS/leveling points distributed all over Cameroon are compared to each DEM,for their vertical accuracy determination.Traditional and robust statistical measures,normality test,outlier detection and removal were used to describe the vertical quality of the DEMs.The test of the normality rejected the hypothesis of normal distribution for all tested global DEMs.Overall vertical accuracies obtained for the three models after georeferencing and gross error removal in terms of Root Mean Square(RMS)and Normalized Median Absolute Deviation(NMAD)are:AW3D30(13.06 m and 7.75 m),SRTM 1(13.25 m and 7.41 m)and ASTER GDEM 2(18.87 m and 13.30 m).Other accuracy measures(MED,68.3% quantile,95% quantile)supply some evidence of the good quality of AW3D30 over Cameroon.Further,the effect of land cover and slope on DEM vertical accuracy was also analyzed.All models have proved to be worse in the areas dominated by forests and shrubs areas.SRTM 1 and AW3D30 are more resilient to the effects of the scattering objects respectively in forests and cultivated areas.The dependency of DEMs accuracy on the terrain roughness is evident.In all slope intervals,AW3D30 is performing better than SRTM 1 and ASTER GDEM 2 over Cameroon.AW3D30 is more representative of the external topography over Cameroon in comparison with two others datasets and SRTM 1 can be a serious alternative to AW3D30 for a range of DEM applications in Cameroon.
基金supported by the Spark Programs of Earthquake Sciences(XH14069Y)the Special Earthquake Research Project of the China Earthquake Administration(201208009)
文摘A broad view of present-day 3D deformation field around the Northeast China region was derived from GPS and leveling observations. We draw the following conclusions： First, the Northeast China region moved towards northwest with an average velocity of 5 ram/a, with respect to South China. The entire Northeast China region was in a low strain state from the strain rate field. Second, we processed two periods of first- order leveling data in 1970s and 1990s, showing the vertical deformation of the Northeast China region is ＂uplift in western part and subsidence in eastern part＇
