Validation of the Tandem-X Intermediate Digital Elevation Model with Airborne LiDAR and Differential GNSS in Kruger National Park

The recently released TanDEM-X intermediate digital elevation model (IDEM) product by the German Aerospace Center (DLR) provides elevation models at 12-m spatial resolution and above. It was derived from bistatic synthetic aperture radar (SAR) interferometry using the two TerraSAR-X satellites flying in close constellation. The aim of this study was to validate the vertical accuracy of the IDEM data at study sites in the Kruger National Park, South Africa. Two validation locations are presented: a dried up former reservoir (Nhlanganzwani Dam) characterized by bare soil and grassland and the peninsula between the Sabie and Sand Rivers near Skukuza characterized by dense woody cover. The results show that the IDEM elevation data are affected by residual vegetation canopy height and landform features smaller than the IDEM resolution cell. The scattering phase centers are located in the canopy but at a lower height than the location of the LiDAR first return signal. When only LiDAR ground hits or differential GNSS ground survey points are used for comparison, the IDEM data have an rmse <; 1 m and a small bias of less than 0.25 m in moderate terrain.