A georeferencing technique incorporating a relief effect for imagery without attitude and orientation information

Most applications using remote sensing need the imagery to be georeferenced, and precision plays a fundamental role whenever cartographic or 'metric' aims are involved. Orthoimage generation techniques produce geometrically corrected images in which also the shift caused by reliefs is evaluated and removed. In addition to a digital terrain model (DTM) of the area, these methods require information on the orientation of the image and the attitude of the sensor-borne platform or, more in general, on the geometry of acquisition. In the case of satellite imagery, this information is not always available or accurate, in particular when sub-scenes have been extracted from a full frame. In this work a new georeferencing technique is presented which corrects the geometrical distortion due to the presence of reliefs. As auxiliary data, the proposed method needs only a DTM of the area and the identification of a set of ground control points, but information on the geometry of acquisition or on the characteristics of the sensor is not required. Two 3-D splines including height information are used, chosen so that they correctly match the ground control points and diverge far from them in linear manner. The proposed method appears to be more accurate compared to the use of polynomial best fit, because the high-frequency distortions due to height variations are accounted. for. Tests have been performed on an area including high-altitude variations. ©2005 Copyright SPIE - The International Society for Optical Engineering.