Accuracy assessment of open DTM and DSM products in urban environments

The digital terrain model (DTM) and digital surface model (DSM) are fundamental data used in many geospatial applications. There are several global open DTM and DSM products. Though previous studies have evaluated open DTM products in high-relief mountain and coastal regions, their performance in urban environments characterized by rapid urban expansion, complex land cover, and high-rise buildings remains insufficiently understood. In this study, we evaluated the elevation accuracy of seven open DTM and DSM products, including ASTER, AW3D30, FABDEM, Copernicus DEM GLO-30, NASADEM, SRTM, TanDEM-X 30 m EDEM in two urban environments in the cities Nanjing and Hong Kong of China. Differential GPS, the ATL08 product of Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2), and airborne LiDAR-derived DTM and DSM were used as references. Results demonstrate that when used as a DTM, FABDEM exhibits the highest accuracy, with normalized median absolute deviation (NMAD) less than 2.2 m in Nanjing and NMAD less than 5 m in Hong Kong. Yet, FABDEM shows systematic underestimation of elevation in both study areas across all land cover types, possibly due to overcorrection of height bias. When evaluated as DSMs, none of the products achieved a high level of performance, with none reaching NMAD < 2 m or LE90 (90% line error) <10 m. GLO-30 demonstrated relatively higher accuracy. Furthermore, we observed a notable contrast in the performance of TanDEM-X 30 m EDEM: it was the second-worst performing DSM in Nanjing but the best in Hong Kong. Our study underscores that modeling Earth’s surface (DSM) is more challenging than modeling bare-earth terrain (DTM). Therefore, future research should emphasize improving the accuracy and reliability of DSMs.