Optimal Orbit Altitude of Satellite Formations for Across-Track SAR Interferometry

Interferometric synthetic aperture radar (InSAR) is a well-known technique for a wide range of remote sensing applications, among which is the generation of accurate, high-resolution digital elevation models (DEMs). The selection of the orbit altitude for InSAR systems is currently based on the heritage of previous SAR missions, for which altitudes lower than 500 km are typically avoided. This paper presents a novel criterion for optimizing the orbit altitude for InSAR missions when considering a formation of two or more satellites. Such a criterion is based on the minimization of the total energy required by the instrument and the control system while ensuring DEM accuracy and posting over a given observed area. This work considers both the well-known helix formation and an innovative fixed-baseline configuration and showcases specific design examples that combine the potential of both options. The analyses show that orbit altitudes around 400 km, i.e., lower than those that are typically considered nowadays, lead to a reduction of energy consumption, especially as the orbit duty cycle increases. The increased energy demand of the control, in fact, is compensated by the decreased energy demand of the radar. Additionally, when a satellite formation operates with short fixed baselines once per month, the increase in energy demand per orbit of a traditional helix configuration has a minimal impact on the system design while providing notable observation advantages. The outcomes of these analyses are of paramount relevance for the design of optimized future InSAR missions for DEM generation.