The effectiveness of swath reconstruction algorithms in cross-track multistatic synthetic aperture radar (SAR) constellations heavily relies on the precise positioning of individual spacecrafts. Ideally, a static array configuration is desired, where the satellites are evenly distributed in a Local Vertical Local Horizontal (LVLH) frame, emulating a fixed antenna. However, achieving this ideal configuration is not feasible without the implementation of constant active control to counter the relative dynamics between the satellites. Alternatively, it is possible to design natural trajectories that yield the desired formation geometry for a significant portion of the orbital period.In this paper, we present a comprehensive analysis of the feasibility of a continuous control concept for building a static array in space. Additionally, we propose suitable formation strategies that eliminate the need for continuous control.

Geosynchronous synthetic aperture radar (SAR) missions offer the advantage of conducting multiple sub-daily interferometric acquisitions using a single platform. However, this comes at the expense of increased fuel and power budgets, due to the significant distance to Earth’s surface. Consequently, such missions are suited for delivering SAR products with relatively lower spatial resolutions, typically in the range of hundreds of meters, over large localized areas spanning more than one million square kilometers. Alternatively, a constellation of small SAR satellites operating in low Earth orbits (LEO) can also deliver similar interferometric products. In LEO, the reduced free-space propagation losses and simpler orbit insertion can be exploited to realize and operate a larger constellation of LEO-SAR satellites. This paper provides an equivalence framework between the two alternatives in terms of interferometric lags and coverage. It further outlines an example mission concept, equivalent to Hydroterra, one of ESA’s Earth Explorer 10 candidate missions.

We present in this paper an algorithm for the estimation of synchronisation phase errors in bistatic and multistatic SAR systems with azimuth diversity, such as multi-channel architectures or azimuth constellations, solely based on the evaluation of the received bistatic data. The suggested algortihm working with unfocussed SAR data shows more robustness against processing errors when compared to the current literature. The relevance of the approach is enhanced by the current interest in both multi-channel SAR architectures and companion SAR missions.

We present in this paper a sensitivity analysis of swath reconstruction algorithms for multistatic SAR constellations, mainly focused on geometric aspects of the formation, such as the irregularity of the sampling and the tilt.

Phase synchronization is a crucial requirement for bistatic and multistatic SAR missions. One possible solution for this problem could be to use the same master oscillator for the radar payload and the GNSS receiver, which could allow the recovery of the oscillator phase noise from the carrier phase measurements. This solution would be cost-effective and straightforward, but its effectiveness depends on whether the GNSS receiver would maintain the spectral purity of the master oscillator internally. We executed zero and short baseline experiments to evaluate this technique with a commercial receiver. Despite some unexpected signatures on the carrier phase single-difference measurements, we achieved frequency synchronization of less than 10 ppm and phase synchronization of less than one degree at the L1 carrier frequency after applying a moving average filter of one second at a 10 Hz sampling rate. The results suggest the feasibility of the GNSS-based phase synchronization concept, but further experiments are necessary to evaluate it thoroughly.