COMPARISON OF DERIVATIVE TOPOGRAPHIC SURFACES OF A DEM GENERATED FROMSTEREOSCOPIC 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 topog raphic surfaces: slope gradient, incidence value, and profile curvatur e. The raw DEM surface is observed to contain a systematic pattern of noise, and analysis of semivariance is used to determine an appropriat e window size for filtering. Field measurements of slope gradient, inc idence 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 correlat ion 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 12.5 degrees to 7.6 degrees. The results e mphasize the caution that must be used before using the digital elevat ion model and its derivative topographic surfaces as estimates of the true landscape configuration.