Improving geometric accuracy of optical VHR satellite data using Terrasar-X data

The very high geometric accuracy of geocoded data of the TerraSAR-X satellite has been shown in several investigations. This precision has been reached fully automatically without any human interaction and is due to good sensor calibration, high accuracy of satellite position and the low dependency on the satellites attitude solution. High resolution optical images from space don´t show this high geometric precision and need further ground control information, which is mainly due to insufficient attitude knowledge. Therefore TerraSAR-X data can be used as ¿ground control¿ to improve the exterior orientation and thereby the geometric accuracy of orthorectified optical satellite data. The technique used is the measurement of identical points in the images, either by manual measurements or through local image matching using adapted mutual information (MI) and to estimate improvements for the exterior orientation or Rational Polynomial Coefficients (RPCs). To be able to use this intensity based method, the radar data have to be filtered before starting the matching procedure. Through adjustment calculations falsely matched points are eliminated and an optimal improvement for the attitude angles is found. The optical data are orthorectified using these improvements and the available DEM. The results are very promising and compared using conventional ground control information from maps or GPS measurements.