Efficient Processing for Far-From-Transmitter Formation-Flying SAR Receivers.

In the framework of passive multistatic radars, formation-flying synthetic aperture radar (FF-SAR) represents an intriguing remote sensing solution due to the enhanced imaging capabilities with respect to the conventional SAR. In this article, we focus on FF-SAR systems operating in a far-from-transmitter geometry, developing a signal model suited to this specific configuration. Additionally, we present an efficient processing scheme that, by properly combining the received raw echoes in a coherent fashion, enables two peculiar imaging modes of FF-SAR, namely, signal-to-noise ratio (SNR) improvement and high-resolution wide swath (HRWS). Simulation results show that achieved radiometric and geometric imaging performances are in line with those offered by an equivalent monostatic SAR. In HRWS imaging mode, azimuth ambiguity suppression and SNR improve as the number of satellites increases and are maximized by specific receivers along-track baselines, whose expression is provided. Finally, we present a statistical analysis of the processing performance parameters for random receivers' positions, both assuming a fixed pulse repetition frequency (PRF) and allowing for an adaptive PRF tuning. This last analysis is also directly applicable to clusters of SAR receivers not far from the transmitter.