The Digital Elevation Models (DEMs) are used to represent the topographic surface of the earth as it is used in many applications. Nowadays, many free DEMs are available online. This study aims to assess the accuracy of six free DEMs. This research uses the GPS observations to determine the elevation stations in the study area by using the Post-Processing Kinematic (PPK) technique and compares these elevations against the elevations computed at the same stations by using six free online Digital Elevation Models (DEMs): SRTM 1 Arc-Second, ASTER 1 Arc-Second, NASADEM 1 Arc-Second, SRTM 3 Arc-Second, GTOPO30, and ALOS PALSAR 12.5 m to find the best results from the free DEMs. The elevations of all stations of different data sources were calculated using the geoid model EGM96. The results indicate that the DEMs that give the best results in this study are obtained from NASADEM 1 Arc-Second, where (RMSE is 2.99 m, and the SD is 2.97 m), and SRTM 3 Arc-Second, where the (RMSE is 3.70 m, and the SD is 3.53 m).
