Evaluation of radargrammetric DEM from RADARSAT images in high relief areas

This paper addresses digital elevation model (DEM) generation with RADARSAT synthetic aperture radar (SAR) fine mode images (F2-F4 and F1-F5) over high relief areas. Shallow look angles and small intersection angles were chosen to reduce layover and radiometric differences in the stereo images and thus increase the performances of the image matching. The radargrammetric DEMs are thus evaluated as functions of processing methods (stereo viewing and editing) and different geometric parameters (intersection angle and derivative topographic surfaces). The first results show that the ground control points (CCPs) must be acquired with stereoscopic viewing instead of monoscopic viewing to avoid an error increase of over 30% in the DEM. An error of one pixel for the image matching has been estimated. The DEMs have also to be edited with semi-automatic and stereo viewing to increase their coherence and consistency, mainly at mountain ridges and lakes. The results also show that a 50% decrease in the intersection angle (80 versus 40) resulted in only a 15% decrease in DEM accuracy (24 m versus 28 m), in contradiction with the theory. Finally, the DEM accuracy is almost linearly correlated with the terrain slopes but not with the terrain aspect (expect better results for the foreslopes).