Quality Assessment of merged NASADEM products for varied Topographies in India using Ground Control Points from GNSS

NASADEM (NASA Digital Elevation Model) is a merged digital elevation product prepared by the National Aeronautics and Space Administration (NASA) from SRTM (Shuttle Radar Topography Mission) DEM as primary data along with other secondary datasets generated from remote sensing-based techniques like satellite photogrammetry and spaceborne LiDAR. These DEM products of NASADEM are reanalysis datasets produced from SRTM and datasets such as ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) DEM; Ice, Cloud, and land Elevation Satellite (ICESat) - Geoscience Laser Altimeter System (GLAS) elevation datasets; and Advanced Land Observing Satellite (ALOS) - Panchromatic Remote-sensing Instrument for Stereo Mapping (PRISM) DEM datasets, available at other locations globally. Three sites were chosen, namely Kendrapara (Odisha), Jaipur (Rajasthan), and Dehradun (Uttarakhand) with plain, moderate, and highly undulating terrain conditions for the assessment of NASADEM. The RMSE results were compared with other merged DEM products namely EarthEnv-DEM90 and MERIT (Multi-Error-Removed Improved Terrain) DEM. The ground control points (GCPs) collected through differential GNSS (DGNSS) surveys were used for the assessment of vertical accuracy and the statistical parameters, such as mean error (ME), mean absolute error (MAE), and root mean square error (RMSE). The RMSE of 4.71m at the Dehradun site depicts that in undulating regions NASADEM is performing better than both EarthEnv-DEM90 and MERIT DEM. However, in the case of urban and plain regions, the performance of MERIT DEM and EarthEnv DEM is superior to that of NASADEM.