In the past decade, significant advances in global elevation modelling have been made with the release of the space-borne SRTM “Shuttle Radar Topography Mission” and ASTER “Advanced Spaceborne Thermal Emission and Reflection Radiometer” elevation data sets. Since a number of applications may rely solely on SRTM and/or ASTER GDEM, it is important to assess the quality of these DEMs using accurate data and precise techniques as well as finding simple but applicable approaches to improving these valuable free access DEMs. To doing so, present study has focused on comprehensive methods include DEM error quantification, DEM error distribution pattern as well as DEM statistical enhancement model. After LiDAR, SRTM and ASTER GDEM data preparation, at the first step, validation of SRTM v4.1 and ASTER GDEM v.2 have been examined using LiDAR information as truth data. Various visual, empirical, and analytical approaches were used as methods. Determination the impacts of terrain characteristics on SRTM and ASTER GDEM DEMs error distribution was next stage which have been done using determination of slope and aspect effects on DEM error distribution pattern in study area. Subsequently, techniques for SRTM and ASTER GDEM enhancement have been investigated by testing varied interpolation approaches on output DEM’s quality. Regression model as a next method have been applied on interpolated DEMs for acquiring better-enhanced results. Finally, to evaluate the effects of improvements approaches on SRTM and GDEM, quantification of DEM errors was done again, and amount of RMSE and statistical parameters was calculated for enhanced SRTM and ASTER GDEM. To sum up, Results could showed us, despite last version of ASTER GDEM has finer pixel size and its validation team claims its vertical accuracy is near to 17 meter (while for our case study 28 meter), still SRTM has better quality and is more reliable than GDEM. Improved RMSE of near 15 m versus 28 meter in original data for ASTER GDEM and 10 Meter opposite 19 meter for SRTM were the results of DEM enhancement in this study
