Automatic Pole Detection in Aerial and Satellite Imagery for precise Image Registration with SAR Ground Control Points

The world-wide absolute geographic positioning accuracy of optical Satellite imagery is mostly about a few pixels of the image resolution. So for example WorldView-3 images have a CE90 of about 4 m. Also the direct georeferencing without ground control information of aerial imagery is in the same range of one to a few metres. These inaccuracies originate predominantly in uncertainties of angular measurements for the sensor attitude. An angular error of only one arc-second at a satellite 750 km above ground results in an absolute error on ground of 3.6 metres. On the other hand radar satellites like TerraSAR-X or TanDEM-X do not measure angles but signal runtimes. So if we identify the same point in an optical image and in a radar image we can solve the problem of inaccurate angle-measurements in the optical sensor models and are able to georeference optical images world wide absolute to below one pixel. In this paper we present a method for identification of point-objects which can be detected in both types of images: the footpoints of poles. If such a footpoint of a pole can be detected simultaneously in both types of images the geoposition of the optical image can be corrected to the accuracy of the point-measurement in the radar image. To achieve a high accuracy also a nearly perfect correction of all errors in signal propagation times of the radar signals has to be conducted. In this paper we describe how the footpoints of poles will be extracted in optical spaceborne or air-borne imagery and how these footpoints are correlated to the potential footpoints of poles detected in the radar imagery