The Shuttle Radar Topography Mission (SHTM) 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 ''.
