High resolution SAR radargrammetry. application with COSMO-SkyMed spotlight imagery

The availability of new high resolution radar spaceborne sensors offers new interesting potentialities for the acquisition of data useful for the generation of Digital Surface Models (DSMs). Two different approaches may be used to generate DSMs from Synthetic Aperture Radar (SAR) data: the interferometric and the radargrammetric one. At present, the importance of the radargrammetric approach is rapidly growing due to the new high resolution imagery (up to 1 m GSD) which can be acquired by COSMO-SkyMed, TerraSAR-X and RADARSAT-2 in Spotlight mode. In this respect, it is well known that the two main steps for DSMs generation from SAR imagery according to the radargrammetric approach are the stereo pair orientation and the image matching. In this paper the topics related to image orientation of SAR stereo pairs in zero-Doppler geometry acquired by COSMO-SkyMed sensor in Spotlight mode are investigated. The defined and implemented model performs a 3D orientation based on two range and two zero-Doppler equations, allowing for the least squares estimation of some calibration parameters, related to satellite position and velocity and to the range measure. The model has been implemented in SISAR (Software per Immagini Satellitari ad Alta Risoluzione), a scientific software developed at the Geodesy and Geomatic Institute of the University of Rome “La Sapienza”. Starting from this model, based a on geometric reconstruction, also a tool for the Rational Polynomial Coefficients (RPCs) generations has been implemented. To test the effectiveness of the new model, two stereo pairs, acquired by COSMO-SkyMed in Spotlight mode over the test sites of Mausanne (Southern France) and Merano (Northern Italy), have been orientated varying the number of Ground Control Points (GCPs) and independent Check Points (CPs). The results obtained clearly show that the geometric potentialities of COSMOSkymed SpotLight stereo pairs as regards 3D surface reconstruction is at the level of about 3 meter, even with quite few GCPs