Gigantino, Antonio (2025) Processing and applications of bistatic and multistatic SAR in a long-baseline configuration. [Tesi di dottorato]

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Abstract

The objective of this PhD research is to investigate the capabilities of bistatic and distributed Synthetic Aperture Radar (SAR) systems when operated in long-baseline configurations. To this end, two main topics have been addressed: image processing and higher-level applications for both the bistatic and the distributed cases. Suitable algorithms have been developed, and comprehensive analyses have been carried out for each of them. Regarding processing, several solutions have been proposed in the scientific literature for combining images in distributed SAR systems. Different algorithms can be adopted depending on the goals of the multi-platform reconstruction and on the required performance improvements with respect to a single receiver. However, all these solutions have been specifically designed for distributed systems operating in quasi-monostatic configurations, i.e., with negligible separation between the transmitter and receiver. Although similar in principle, extending these algorithms to long-baseline scenarios is not straightforward and requires addressing the distinctive features of this observation geometry. This thesis tackles these challenges by proposing a multi-platform image synthesis algorithm that combines a time-domain focusing approach with a null-steering beamforming technique and including strategies tailored to handle long-baseline configurations. The performance of this technique is thoroughly analysed. First, time-domain focusing is implemented and tested in the bistatic SAR case using simulated SAR images generated within a specifically developed simulation environment. Then, the capability to suppress azimuth ambiguities is assessed with respect to different geometrical configurations of the system, such as the spatial distribution of receivers and their separation from the transmitter, taking as a reference the case of RODiO mission. Finally, an alternative solution is proposed for cases where the primary algorithm is not effective. Concerning applications, this research focuses on developing and analysing techniques that can benefit from long-baseline configurations and provide valuable high-level bistatic products. Three applications have been identified: the generation of a Radargrammetric Digital Elevation Model (DEM), ship detection over the sea, and ship velocity estimation. The advantages of each product compared to their monostatic counterparts are discussed, along with the fundamental principles behind them. For each application, the developed algorithm is presented, detailing the most relevant processing steps, and validated using either real representative data or simulated datasets. Performance assessment techniques are also described and applied to a reference mission scenario, namely PLATiNO-1. Additionally, an application for distributed SAR systems is investigated: multi-baseline along-track interferometry. The main advantages reported in the scientific literature are presented, together with preliminary considerations on the potential implementation of this technique in the future RODiO mission.

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