A Robust Technique for Precise Registration of Radar and Optical Satellite Images

Abstract

Combining data from different sensors for visual or classification analysis is a common task in remote sensing. The first step is normally to register the images which may be considered geometric integration; the accuracy of this step is important to create a valuable final hybrid image. This paper addresses geometric integration and introduces a new method for automatically registering two dissimilar images, such as, a radar image and an optical image with high accuracy. Pre-registration of the two images to within a specified tolerance is required. In our examples, this tolerance is up to 17 pixels (at the scale of the higher resolution image) and may be achieved by, for example, visually located control points. The described approach then uses large-scale edge gradient contours in a process that automatically locates candidate control points on the contours. The points are selected using a cost function that measures the degree of match between all possible pairs of points. Numerous control points (typically around 50 pairs) are found from matched pairs of gradient contours and used in a global, rubber sheet, polynomial warp to refine the registration. This approach is applied to register a Synthetic Aperture Radar (SAR) image (ERS2, 12.5 m pixels) and a Thematic Mapper (TM) optical image (Landsat-5, 28.5 m pixels) automatically. Several examples with different scene content are shown to validate the approach and discussed in terms of residual registration error and processing efficiency.