Precise Orientation of Spot Panchromatic Images with Tie Points to a Sar Image

The extraction of spatial data from satellite imagery requires that precise sensor models are used to orientate images. This is particularly important with images acquired by linear sensors, such as SPOT, frequently pointed with large incidence angles. Image orientation with pixel accuracy requires that accurate ground control points are used. The acquisition of ground control is especially difficult in remote areas, where satellite images are important data sources for the production and updating of topographic maps. This paper describes a method for the orientation of SPOT panchromatic images making use of tie points with a SAR image. SAR and SPOT images compose stereo-pairs with a good stereo intersection, from which heights can be derived. For the SAR-SPOT tiepoints, approximate heights are derived from parallaxes and can be corrected using altimetric ground control points. The method described makes use of the fact that the SAR image orientation can be derived from the orbit and SAR processing parameters, provided with SAR images, and does not require ground control points. The paper reports on a study carried out with SPOT and Radarsat images from Portugal. Accuracy assessments were done with digital cartography and field surveyed GPS data. It was possible to conclude that using a SAR image, accurate SPOT image orientation can be achieved requiring only very few altimetric control points.