Advances and Limitations in a Parametric Geometric Correction of Chris/proba Data

RESUME The geometric correction of remote sensing images is a preprocessing step required for most applications and studies. The success of CHRIS/PROBA as scientific mission is producing a large archive of image sets that is continuously growing. Although the geometric correction problem is already solved by means of ground control points (GCP) or image corregistration techniques, these methods require intense human intervention. Therefore they are not convenient for processing large number of images. For this reason the development of a quasi-automatic parametric algorithm for geometric correction of CHRIS/PROBA data was undertaken by our group. This work has given rise to some questions about the image acquisition procedure. As a result new information about the operation of CHRIS/PROBA has recently become available for the user community, pointing out that the operation for acquisition is based on time, instead of fixed fly-by zenith angles (FZAs), as was documented previously. It also states that to determine each particular acquisition the system assumes a circular orbit with radius equal to the semi-major axis. This paper presents a study of the implication that the new information has on how the parametric algorithm must be implemented, as well as the impact on the acquisition geometry, the observation angles, and the pointing accuracy.