Evaluation of slopes calculated from TanDEM-X digital elevation models at 3 spatial resolutions

The three resolutions of the TanDEM-X DEM show the effects of resolution on calculated slopes.  We compare those slopes with independently derived lidar DEMs at the same spatial resolutions (0.4, 1, and 3 arc seconds).  The TanDEM-X 0.4 arc second DEM shows significant differences from lidar derived DEMs at the same resolution, and generally has more variability which may be due to radar speckle, while the 1 and 3 second DEMs have very similar slope characteristics as the lidar DEMs.  The slopes decrease as the DEM spacing increases, but the rate of decrease does not vary systematically.  Slopes all increase with latitude.