Accuracy assessment and enhancement of global DEMs for drainage morphometric analysis: a case study from Aïn Leuh Region, Morocco

The purpose of this study was to evaluate and improve the vertical accuracy of three free global digital elevation models (DEMs)—the Shuttle Radar Topography Mission (SRTM), the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), and the Forest and Buildings Removed Copernicus DEM (FABDEM). The vertical accuracy of the DEMs was evaluated through a survey of 3551 points using a Real-Time Kinematic global positioning system (RTK-GPS) in Aïn Leuh, Morocco. The findings indicated that the SRTM and FABDEM DEMs have a root mean square error (RMSE) of ± 7.25 m and 6.53 m, respectively, surpassing the ASTER DEM (± 8.12 m). Interpolation methods were then employed to correct and improve the DEMs using the surveyed GPS data at 15 m and 30 m spatial resolutions. Five interpolators were used: Inverse Distance Weighting (IDW), Natural Neighbor, Spline, ANUDEM, and ordinary kriging (OK). By integrating the GPS data with the DEMs, the interpolation methods were able to improve the accuracy of the models. However, it is worth noting that ANUDEM algorithm outperforms other algorithms in terms of accuracy and the surface's natural appearance of topography. Furthermore, our findings indicate that resampling to a 15-m spatial resolution achieves an appropriate balance between improving the DEM’s quality and revealing topographic features that weren’t discernible in the raw DEMs. The suggested approach resulted in a 49% reduction in errors compared to the raw DEMs. The RMSE values for the resampled DEMs were ± 3.6 m and ± 3.3 m for the SRTM + GPS and FABDEM + GPS, respectively.