SAR IMAGE GEOCODING USING A STEREO-SAR DEM AND AUTOMATICALLY GENERATED GCPs

SAR image geocoding needs an accurate DEM, but such a DEM can be difficult to obtain. This paper shows that the needs of geocoding can be satisfied using the DEM generated by employing a rigorous geometric model and an optimized least squares correlation method with a region-growing approach. The geometric model used is independent of any manually selected GCPs and is robust to orbit errors. The required number of GCPs for correcting any systematic effects after space intersection is only two. When good quality orbit information is unavailable, GCPs or tie points are essential for SAR image geocoding, but selection and measurement of these points is often difficult. This paper proposes a SAR simulation technique to automatically provide control for geocoding without manually selected GCPs or tie points. The GCPs were generated using a small known DEM chip of size 1km by 1km with significant terrain relief. The RMS errors of the four automatically generated GCPs are less than 3.4m in range direction and 4.6m in azimuth direction. RADARSAT SAR images have been tested using a reference DEM and an automatically generated DEM to produce geocoded images. The RMS errors of the check points range from 13m to 21m in easting and 16m to 21 in northing. The results derived in this paper demonstrate that the stereo-SAR generated DEM can be used for geocoding in flat-moderate areas, and a higher level of automation can be achieved.