Satellite-derived digital elevation model accuracy: Hydrogeomorphological analysis requirements

Digital elevation models (DEMs) are currently generated using satellite imagery, but little is known about how errors in satellite-derived DEMs affect hydrogeomorphological products such as relief, elevation contours, basin boundaries and stream networks. This study identified and minimized vertical errors for a SPOT-derived DEM of the 532 km2 Little Washita River, OK, watershed and then assessed how elevation inaccuracies affected hydrogeomorphological analyses. SPOT-derived DEM errors were identified using a set of ground control points (GCPs) and by comparing the 600000 pixels comprising the SPOT image of the study area to high and low accuracy US Geological Survey (USGS) 7.5-minute airborne-derived DEMs. The comparative analysis identified a basin-wide error structure in the SPOT product that post-processing of the SPOT image then reduced from an RMSE of 8.7 to 4.5 m. Although SPOT- and USGS-derived topographic relief images had a poor correlation at small spatial scales, at larger hillslope scales nearly 90% of the image pixels overlapped. For basin-scale descriptors, such as catchment area, stream length, stream density and Horton ratios, SPOT- and USGS-derived estimates differed by no more than 3%. At smaller spatial scales, however, an overlay of SPOT-derived vector images of basin boundaries and stream networks with equivalent higher accuracy products revealed that the products were incongruent on average at 100 m and at most up to distances of 1 km. In summary, the accuracy of the SPOT-derived DEM was adequate for deriving estimates of basin average hydrogeomorphology but was unable to match equivalent products derived from USGS 7.5-minute DEMs at scales finer than 100 m.