Orbit determination requirements for synthetic aperture radar

The formation of high fidelity focused synthetic aperture radar (SAR) imagery requires accurate knowledge of the radar-scene imaging geometry. For the case of a space based SAR system this implies accurate knowledge of the orbit of the platform. In order to determine the required accuracy for a given orbital SAR, the tolerance of the focusing parameter to inaccuracies in the parameters describing the orbit must be determined. This has traditionally been performed by describing the imaging geometry in terms of the local heading of the satellite and the direction of pointing of the radar beam relative to the motion of the satellite. A more intuitive description of the orbit is to describe it in terms of the Keplerian elements of the platform. The derivation of the focusing range polynomial of a space based SAR from the Keplerian elements that describe the orbit are presented. The tolerance of each of these elements to SAR focusing is then derived for a typical high resolution space based SAR system. These tolerances are then be related to the polar position and velocity measurement accuracy required of an orbit determination sensor. It will then be shown that even at very fine resolution, inaccuracies in the orbit determination will have little effect on SAR image formation.