Coherent Multistatic UAV-Based SAR

Multistatic synthetic aperture radar (SAR) with unmanned aerial vehicles (UAVs) as platforms enables applications not possible with monostatic SAR by spatially separating transmitter and receiver. Single-pass interferometry and tomography or the analysis of different scattering mechanisms become feasible while having the large flexibility of UAV-based systems. In order to fully exploit the advantages, the single nodes have to operate cooperatively. Coherency is required in time, frequency, and phase. In conventional approaches these requirements necessitate high synchronization accuracies. In this work, a highly scalable concept is introduced that utilizises receive-only nodes and a dedicated transmitter in contrast to typical passive radar techniques. Radar and reference signal required for demodulation are both received, directly sampled, and stored locally onboard the UAV. The high demands on timing accuracy translate into localization accuracy, which is needed for SAR processing anyway. Coherency is created in postprocessing by digital demodulation, allowing for phase coherent SAR imaging. The processing steps are explained and the influence of possible error sources is analyzed. The concept is validated by static radar measurements as well as a bistatic UAV-based SAR experiment of a realistic scenario.