Correction of errors in SPOT-Derived DEM´s using GTOPO30 data

In hydrological studies of the Little Washita River Watershed, OK, a 1000 km² section of a satellite probatoire d´observation de la terre (SPOT)-derived digital elevation model (DEM) was observed to contain systematic elevation errors, and a technique for minimizing these errors was developed. Error minimization was achieved by first overlaying the Little Washita section of GTOPO30, the latest DEM providing global land coverage, and then computing GTOPO30-SPOT elevation residuals. Spatial analysis of these elevation residuals revealed a systematic elevation error oriented about a single axis, and rotating the SPOT-derived DEM scene about this axis minimized the GTOPO30-SPOT root mean square error (RMSE) by nearly 10%. The axis intercept, slope, and degree of rotation identified using the relatively coarse 1 km resolution GTOPO30 product were nearly identical to those identified using three separate DEM´s of 30 and 90 m resolution. Forty ground control points (GCPs) not used in the original stereocorrelation of the SPOT-derived DEM confirmed that rotation improved the Little Washita SPOT-derived DEM RMSE by nearly 26%. This research indicates that 60×60 km² SPOT-derived DEM scenes may have interior subsections that contain systematic elevation error, and that the GTOPO30 data set has an adequate systematic accuracy for identifying and correcting this error