Study On Generating DEM From Radarsat Stereo Images With Photogrammetry Methods

As a kind of positive sensor working with microwave, Synthetic Aperture Radar (SAR), which has the capacity of penetrating clouds to some extent, can observe the earth day and night and whole weather. It has some advantages that traditional optical and optoelectronic camera does not possess. SAR technology provide a new way to the topography mapping in the cloudy, rainy, and vegetate-covered areas.Radarsat is a SAR satellite launched in November 14, 1995 by Canada. It can obtain the SAR stereo images in two orbits. How to make use of the abundant SAR image resources to accomplish the task in which the traditional photogrammetry can't succeed is a challenge faced with us.The main emphasis of this paper is the study on the methodology of generating DEM from Radarsat image stereo pairs. In this paper , the principle of SAR formation image is briefly analysed firstly, the features of SAR image and specalities of stereo model made by SAR image pairs are discussed, three kinds of SAR image formation model are compared and analysed. According to the image data possessed, the formation model of equivalent line central projection is adopted to establish the correspondence between image and object space. Based on this model, every point's object space coordinates are calculated by space resection and space intersection. The exterior orientation elements are calculated by single image space resection with GCPs, and the object space coordinates are calculated by double image space intersection. The grid DEM is produced by interpolation. This is the whole flow of generating DEM from SAR stereo images.The calculation of exterior orientation elements is the difficult point of analytical treatment. The algorithm is adopted to overcome the correlation between the exterior orientation elements, in which the linear elements and angular elements are separated into two parts to iterative calculate. Because the SAR stereo model is different from optical image stereo model, the object space coordinates of ground points are calculated by iterative space iteration.The Radarsat image stereo pairs are used as experiment data in this paper. The DEM of test area is generated by using above-mentioned methods. The results of experimentshow that the methodology adopted in this paper is correct, and prove that generating DEM from Radarsat stereo images is practical. This provide a new thought and way for topography mapping in western China.