Geomorphometry from SRTM: Comparison to NED

The Shuttle Radar Topography Mission (SRTM) produced near-global 1 and 3 DEMs. The cartographically-derived National Elevation Dataset (NED) provides a mechanism to assess SRTM quality. We compared 12 geomorphometric parameters from SRTM to NED for about 500,000 sample areas over the continental United States. For basic parameters like average elevation or relief, the two data sets correlate very highly. For more derived measures, such as curvature and higher moments (skewness and kurtosis), the correlations are much lower, with some parameters essentially uncorrelated between the two DEMs. Correlations improve after restricting analysis to region with average slopes greater than 5 percent, and the SRTM data set compares more closely to simulated 2 NED than to 1 NED. SRTM has too much noise in flat areas, increasing average slope, while in high relief areas SRTM over smoothes topography and lowers average slopes. The true resolution of 1 SRTM DEMs proves to be no better than 2 . Introduction Digital elevation models (DEMs) represent the Earth’s surface at a range of scales, and have been widely applied in uses from military terrain analysis through earth science and engineering practice to video games. Even before suitable computers or digital data sets existed, geomorphologists saw the potential of DEMs to enable geomorphometric quantification of ground surface relief and patterns (Evans (1980; 1998); Pike (1988; 2000; 2002)). The Shuttle Radar Topography Mission (SRTM) allowed production of a publicly available, consistent, and comprehensive DEM covering approximately 80 percent of the Earth’s surface. No other publicly available data exists at this resolution, and the SRTM dataset has instantly become the global standard for medium to small scale depictions of topography. Because of the varied applications for which the SRTM data is already being and will be used, we must evaluate and understand how it represents topography and surface morphology. Geomorphometric comparison of SRTM with the best comparable DEM, the National Elevation Dataset (NED, Gesch et al., 2002) will demonstrate how the two sources represent the same surface morphology. The comparison will yield information about SRTM, its systematic characteristics, and its true resolution. Figure 1 provides a visual comparison of the two DEMs. Geomorphometry from SRTM: Comparison to NED