Abstract
This study employs Ice, Cloud and Elevation Satellite-2 (ICESat-2) and the Global Ecosystems Dynamics Investigation (GEDI) observations to generate gridded digital terrain models (DTMs). Specifically, we (1) compared how acquisition characteristics affect the accuracy of ICESat-2 and GEDI observations, (2) assessed the sampling intensity with respect to observation accuracy (0.25–50 m) and grid resolution (90, 300, and 1000 m), and (3) interpolated DTMs at 90 m resolution and compared their accuracy with a global digital elevation model (DEM) Copernicus GLO-90. ICESat-2 data consistently outperformed GEDI footprints in terms of terrain elevation accuracy across a range of conditions (terrain slope, landcover, beam strength, and day/night). Sampling intensity is strongly shaped by the trade-offs between observation accuracy and grid resolution, limiting the coverage at finer scales and stricter thresholds. However, combining ICESat-2 and GEDI boosted sampling intensity, with over 60 % of cells containing at least one observation, which enabled a 90 m DTMs interpolation. The spaceborne lidar DTMs at 90 m resolution achieved RMSEs between 9.9 and 14.7 m, comparable to Copernicus DEM (9.9–15.6 m). However, the local accuracy of the interpolated DTMs depended on both the number of input observations and their accuracy. Where at least 4–6 observations per a 90 m cell with vertical accuracy better than 5 m were available, spaceborne lidar DTMs outperformed the Copernicus DEM, with RMSEs of 3.7 m vs. 11.2 m in forests and 2.6 m vs. 3.1 m in non-forested areas. This demonstrates that spaceborne lidar-derived DTMs could replace global DEMs.