Geolocation enhancement of spaceborne cameras: The SAR-Optic approach

Abstract. As many observation data providers are delivering spaceborne optical images with a resolution close to airborne sources, users are expecting the same level of geolocation accuracy. Unfortunately, locating the line of sight of a camera on the ground from, at least, 500km is still a challenge. It requires a precise knowledge of the camera absolute orientation beyond current technology. Spaceborne SAR images do not suffer from this problem as the location accuracy depends only on the antenna position and speed. An operational approach is presented exploiting the geometric stability of SAR sensors to improve the location accuracy of optical images. It is based on the ability to find correspondences between overlapping SAR and optical images. The refinement of camera orientations is then achieved through photogrammetric (almost) classical techniques. A medium scale validation campaign conducted across France demonstrated an absolute horizontal geolocation accuracy of 1.5m (CE90).