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 affects 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 600 000 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 is 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. Copyright (C) 2000 John Wiley and Sons, Ltd.