A new rigorous model for the orthorectification of synchronous and asynchronous high resolution imagery

This paper proposes a new rigorous model for the orthorectification of high resolu- tion imagery. Firstly, the model was developed and tested in the most general situation, that is considering the asynchronous EROS A satellite; now it is under extension in order to be able to process imagery acquired by other high resolution synchronous sensors (IKONOS II, QuickBird, SPOT 5). Therefore it is necessary to model the high geometric distortions by a rigorous photogrammetric approach that requires the viewing geometry reconstruction through the knowledge of the acqui- sition mode, sensor features and satellite position and attitude. The model was implemented in a C++ software SISAR and some tests were carried out to evalu- ate the intrinsic precision and accuracy achievable by using different angle off-nadir imagery. Results were compared with the corresponding ones obtained by the model implemented in the commercial software OrthoEngine 9.0 (PCI Geomatica), the only rigorous model for EROS A imagery presently available. The comparison shows good agreement on the whole between the software as regards precision and accuracy; nevertheless, the model implemented in SISAR exhibits more stable dependencies of precision and accuracy on the Ground Control Point (GCP) number. A final specific concern was devoted to the impact of outliers in GCP coordinates: the behav- iours of two rigorous models (OrthoEngine 9.0 and SISAR) were again analyzed and compared to the one attaining to the second order Rational Polynomial Function (RPF) model implemented in OrthoEngine 9.0. In agreement with well-known theoretical deductions, the rigorous models exhibited a good robustness, whilst the RPF model proved to be highly vulnerable and inade- quate for cartographic applications.