A novel radargrammetric model and a RPCs generation strategy: application with COSMO-SkyMed and TerraSAR-X imagery

The topic of this paper is the definition of a geometric model for stereo pair orientation of SpotLight Synthetic Aperture Radar (SAR) imagery collected by the new high amplitude reso-lution radar sensors COSMO-SkyMed (Italian) and TerraSAR-X (German). The suite for radar-grammetric approach 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”. The rigorous 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. Starting from this model, according to a terrain independent scenario, an additional tool for the Rational Polynomial Coefficients (RPCs) generation has been implemented. In this last respect, it has to be noticed that only the imagery collected by the high amplitude resolution radar sensor RADARSAT-2 (Canadian) are presently supplied with RPCs. In order to validate the orientation model and the RPCs generation strategy, they were applied to imagery collected over three test sites. The first test site is a zone of Merano (Northern Italy), the second test site is the San Pietro Island (Sardinia, Italy), where SpotLight images were acquired by COSMO-SkyMed; the third test site is Hannover (Northern Germany), where imagery were acquired by TerraSAR-X. The results obtained and here discussed clearly show that the geometric potentialities of COSMO-SkyMed and TerraSAR-X stereo pairs as regards 3D surface reconstruction is at the level of 2-3 meter both with rigorous model and with generated RPCs.