Quality of Orthorectified TerraSAR-X Products

Abstract

The German Aerospace Center (DLR) has developed the TerraSAR-X Ground Segment. One part is the geocoding system that provides orthorectification capability for multiresolution, multi-polarisation and multi-frequency data. Besides an ellipsoid corrected product a new product called Enhanced Ellipsoid Corrected (EEC) will be offered that considers Digital Elevation Models (DEM) of a moderately coarser resolution then the 1 up to 3 m resolution of the TerraSAR-X modes. SRTM/Xband DEMs with approximately 25 m spacing will be the backbone for this operational and fully automated service. As optional product an Geocoded Incidence Angle Mask (GIM) is available providing information about the incidence angle of the radar beam, as well as about layover and shadow areas. High precision terrain correction using high resolution DEMs, tie-pointing and image adjustment will be implemented in an experimental processor. This paper gives detailed information on the image quality, which is examined in detail based on the first available geocoded TerraSAR-X products. Therefore radiometric and geometric aspects will be investigated. It is to be shown that the orthorectification step does not tamper the original radiometric properties. The geometric accuracy of the orthorectification mainly depends on the quality of the used DEM. Besides the SRTM/X-band DEM additional elevation data like SRTM/Cband, ERS-derived and GLOBE data are used for EEC generation. The achieved pixel location accuracies will be presented. The quality characteristics of the Geocoded Incidence Angle Mask - depending also on the used DEM - are described. Moreover the high precision orthorectified image (called Geocoded Terrain Corrected - GTC) will be examined with regard to pixel location accuracy. A high resolution laserscanning DEM, tie-points and image adjustment will be used for this analysis. Furthermore information regarding processing performance will be given.