" System Calibration, Geometric Accuracy Testing And Validation of DEM & Orthoimage Data Extracted From SPOT Stereopairs Using Commercially Available Image Processing System".

Abstract.

The Paper describes the comprehensive testing of digital photogrammetric modules forming parts of the image processing systems from a number of remote sensing system suppliers-PCI, ERDAS, R-WEL, etc.-for use with SPOT stereo-pairs. The Tests have been conducted over a large area of 12,000 sq.km forming part of the Badia, adesert area located in the north-east of Jordan that is covered by block of five SPOT stereo-pairs. The terrain data available for calibration and testing has included a very high accuracy test field comprising 130 ground control points, whose positions and heights have been established using differential GPS. This supplemented by 150 km of profile data measured using real-time kinematic GPS and by digitized contour data derived from existing 1:50,000 and 1:250,000 scale topographic maps of the area produced using aerial photogrammetric techniques.

The results of a comprehensive series of geometric accuracy tests is given for both Level 1A and 1B image data. This is followed by the results of a series of tests to validate the DEMs and contours derived from the elevation data produced by each of the packages that have been tested. The final results from the validation are surprisingly good, but

only after extensive use of filtering techniques to remove the artifacts and spurious features generated by image matching routines employed by different systems. The results achieved during tests of the individual orthoimages and orthoimage mosaics produced using the SPOT DEM data sets are also given, both in terms of their radiometric quality and their geometric accuracy.

This comprehensive series of tests revealed a number of flaws and shortcomings in all image processing systems that have been calibrated and tested. Some of the more serious flaws are described and discussed in the paper. The finding from the tests resulted in the flawed parts of the varios systems being modified and then re-tested via a highly interactive interchange of programs and data between the authors and the system suppliers-to the benefit of future users of these systems. The test area, having proven its worth, is available for testing of other space image data-including that from the forthcoming commercial high –resolution satellites-in a similar manner to that described in the paper.