Sisar: a Rigorous Orientation Model for Synchronous and Asynchronous Pushbroom Sensors Imagery

The correct georeferencing of remote sensing imagery is a fundamental task in the photogrammetric processing for orthoimages, DEM/DSM generation and 3D features extraction. In this paper we focus on the georeferencing of pushbroom sensors imagery with rigorous model, that is the well known approach based on the collinearity equations. In particular, we developed, implemented and tested a rigorous model for the georeferencing both single images and stereopairs collected by EROS A, IKONOS and Quickbird satellites. The model, implemented in the software SISAR, reconstructs the orbital segment during the image acquisition through the Keplerian orbital parameters, and model the sensor attitude and internal orientation allowing for self-calibration parameters too. As regards estimation procedure, in order to avoid instability due to high correlations among some parameters leading to design matrix pseudo-singularity, Singular Value Decomposition (SVD) and QR decomposition are employed to evaluate the actual rank of the design matrix, to select the estimable parameters and finally to solve the linearized collinearity equations system in the least squares sense. The results are compared with rigorous models included in OrthoEngine (PCI Geomatica); three images are concerned in this paper, showing that SISAR performances are at the level of the OrthoEngine ones. In particular, results stemming from the elaborations of Quickbird and IKONOS imagery show that accuracies at sub-meter level, compatible with cartographic product at 1:5000 scale, are achievable. Future prospects regard the rigorous model extension to Cartosat-1, EROS B and Prism satellites.