NED development included procedures to correct and/or minimize the artifacts found in source DEM files.
DEM's produced by manual profiling techniques were evaluated for data quality and filtered if necessary.
A "mean profile filtering" algorithm was used to reduce the banding artifact observed in profile DEM's. The algorithm isolates the elevation differences that cause the banding, and then subtracts them from the DEM.
The first step is to smooth each row in the DEM independently using a large Gaussian-weighted convolution kernel, up to 101 pixels wide. After this operation, each column consists of a weighted mean of many columns, and constitutes a "mean profile" in the y dimension. The banding artifacts are caused by a systematic operator bias in operating the profiler, and alternate sign from band to band. Since they lie along the x-axis, they are not significantly attenuated by the smoothing operation, and are visibly present in the y-axis mean profiles. By gently smoothing each mean profile with a small convolution window, about the size of a band (7 pixels works well), an array may be constructed of the residuals obtained by subtracting each mean profile from its lightly smoothed version. The resulting profile effectively models the banding. By subtracting these residuals from the original DEM, a largely band-free DEM is obtained. The magnitude of the residuals is under two meters, with an RMS of one meter typical. The resulting data is saved and replaces the input DEM file. This same method works well in removing patch boundary artifacts from DEM produced by the GPM II, though it must be run in two directions. (courtesy of the USGS) | 
