CALIBRATION STRATEGY FOR THE MEDUSA CAMERA SYSTEM

The MEDUSA camera system is a high resolution earth observation instrument designed to operate from a long endurance UAV flying at stratospheric altitudes. Due to the technical constraints imposed on the instrument regarding mass, power and dimensions, the MEDUSA instrument shall experience large temperature variations induced by its varying environment in which it is operated. The induced physical changes of the optical system (lenses and opto-mechanics) imply that the parameters of the geometric camera model of the MEDUSA instrument cannot be assumed to be constant. Generating geometric "correct" images under those circumstances requires a calibration procedure which is able to respond to this dynamic behaviour. This paper presents the calibration strategy for the MEDUSA instrument which is based on a full in-flight self-calibration with block bundle adjustment. A theoretical estimate of the geometrical accuracy of MEDUSA images has been explored. Based on this approach a first sensitivity check to certain temperature variations within the optical system has been addressed. A more detailed study has started making use of a refined image simulator based on the collinearity equations, a camera model and image distortion models. First preliminary results of this approach show the geometric accuracy over the complete image within different temperature windows for a camera model with constant parameters.