Maarten Pronk , Marieke Eleveld, Hugo Ledoux

Digital elevation models (DEMs) are a necessity for modelling many large-scale environmental processes. In this study, we investigate the potential of data from two spaceborne lidar altimetry missions, ICESat-2 and GEDI—with respect to their vertical accuracies and planimetric data collection patterns—as sources for rasterisation towards global DEMs. We validate the terrain measurements of both missions against airborne lidar datasets over three areas in the Netherlands, Switzerland, and New Zealand, and differentiate them using landcover classes. For our experiments, we use three and a half years of ICESat-2 ATL03 data and three years of GEDI L2A data, totalling 252 million measurements. The datasets are filtered using parameter flags provided by the higher-level products, respectively ICESat-2 ATL08 and GEDI L3A. For all areas and land cover classes combined, ICESat-2 achieves a bias of −0.11m, a MAE of 0.43m, and a RMSE of 0.93m. From our experiments, we find that GEDI is less accurate with a bias of 0.09m, a MAE of 0.98 m and a RMSE of 2.96 m. Measurements in open land cover classes, such as “Cropland” and “Grassland”, result in the best precision for both missions. We also find that the slope of the terrain is a major influence on vertical accuracy, and more so for GEDI than ICESat-2, because of its larger horizontal geolocation error. Contrastingly, we find little effect of either beam power or background solar radiation, nor do we find noticeable seasonal effects on accuracy. Furthermore, we investigate the spatial coverage of ICESat-2 and GEDI by deriving a DEM at different horizontal resolutions and latitudes. GEDI has higher spatial coverage than ICESat-2 at lower latitudes due to its beam pattern and lower inclination angle, and a derived DEM can achieve a resolution of 500 m. ICESat-2 only reaches a DEM resolution of 700 m at the equator but increases to almost 200 m at higher latitudes. When combined, a 500 m resolution lidar-based DEM can be achieved globally. Our results indicate that both ICESat-2 and GEDI enable accurate terrain measurements anywhere in the world. Especially in data-poor areas—such as the tropics—this has potential for new applications and insights.