Comparison of Derivative Topographic Surfaces of a DEM Generated from Stereoscopic SPOT Images with Field Measurements

A digital elevation model (DEM) derived from SPOT satellite imagery is evaluated for accuracy in elevation and three of its derivative topographic surfaces: slope gradient, incidence value, and profile curvature. The raw DEM surface is observed to contain a systematic pattern of noise, and analysis of semivariance is used to determine an appropriate window size for filtering. Field measurements of slope gradient, incidence value, and profile curvature are used to evaluate the accuracy of the derivative surfaces. Several processing options are employed to maximize the correlation between the surface representations and the field data. For example, with slope gradient measurements the correlation between field and digital values increased from 0.40 using the raw DEM to 0.78 with a custom-filtered DEM, and the standard deviation of differences decreased from 22.5' to 7.6'. The results emphasize the caution that must be used before using the digital elevation model and its derivative topographic surfaces as estimates of the true landscape configuration.