GEO-SAR Orbit Characteristics derived from the Hydroterra Mission Performance Model

The ESA Hydroterra mission concept is a GEO-SAR satellite aimed to perform interferometric and radiometric observations over different target areas in Europe and Africa. As a GEO-SAR mission, Hydroterra allows for a wide range of different orbits, while facing SAR specific constraints. The question arises to find the best suited orbit for the SAR performance of the mission, given the set of mission requirements and constraints. In this paper, a model for the SAR performance is presented, which allows for a comparison of GEO-SAR orbits for Hydroterra taking into account the varying imaging geometry over one orbit period. This Hydroterra performance model is analysed over a design space of orbits of different observation geometries and dynamics. The image revisit time is the key performance parameter used to evaluate the different orbits. For a fixed instrument, it is demonstrated that orbits with a linear shaped ground-track oriented normal to the target minimize the resulting image revisit time, at the same time fulfilling the interferometric and radiometric product requirements. This model was developed in the frame of the ESA contract Phase 0 System Studies of the Hydroterra Mission.