Digital elevation model (DEM) is a three-dimensional representation of the earth’s surface which provides information regarding the terrain relief. Nowadays, DEM became an inevitable component in remote sensing and GIS because of its requirement in various fields like preparing 3D simulations, run-off modelling, topographic mapping, infrastructural studies, etc. DEMs can be generated using different techniques such as ground surveys, interpolation of contour maps, photogrammetric techniques using satellite stereo images and aerial stereo photographs, interferometry and air borne laser scanning. Some of the open-source DEMs available are SRTM (Shuttle Radar Topography Mission), ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer), GTOPO30 and CARTOSAT-1. Each DEM contains some natural errors (gross, systematic and random errors) depending on technology used in its primary data acquisition and also on processing methodology in relation to the land cover type and particular terrain. The accuracy of these datasets is often unknown and non-uniform within each dataset. In this study, the elevation accuracies were assessed for some freely available DEMs like ASTER, SRTM and CARTOSAT-1. For this work, the study area taken was Prakasam district which lies along the coastal belt of Andhra Pradesh state in India. The study area has diversified terrain relief with hills in western part and plain region on east along the sea coast of Bay of Bengal. As a reference to validate the elevations of DEMs, total 100 ground control points (GCPs) were taken from Google Earth Pro software, in different terrains (accessible and inaccessible) of the study area. Over these GCP locations, the corresponding elevations on SRTM, ASTER and CARTOSAT DEMs were found out using geospatial techniques in QGIS 3.10 software. The RMS errors of elevations for the SRTM, ASTER and CARTOSAT-1 DEMs were resulted as 2.770, 11.71 and 85.33 m, respectively, from WGS84 datum. From the studies, it was observed that, for the study area of this research, SRTM DEM gives the highest accuracy in vertical elevations compared to other DEMs.
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