Development, Implementation, and Analysis of a Multiple-Input Multiple-Output Concept for Spaceborne High-Resolution Wide-Swath Synthetic Aperture Radar

Abstract

Since the development of the first Synthetic Aperture Radar (SAR), radar has become an important sensor for imaging applications. Manifold fields of application ranging from climate change research, over change-detection, and 4-D mapping up to earthquake and flood monitoring are covered by SAR. Especially high-resolution, day- and night-, as well as weather-independent imaging capabilities led to the success of recent spaceborne SAR missions. However, due to a high demand for global SAR data sets, state-of-the-art sensors reach their limits in terms of resolution, swath-width, repeat cycle, and flexibility. To solve SAR-inherent limitations, in this dissertation, a new generation of SAR sensors with multiple transmit and multiple receive channels (MIMO) and Digital Beam-Forming (DBF) capabilities is proposed. Apart from an increased flexibility, this enables a large variety of new operation- and acquisition-modes for high-resolution wide-swath SAR imaging. To separate the individual channels in the post-processing, established processing techniques can not be applied, since SAR is highly sensitive to interferences. Hence, the Space-Time-Frequency Adaptive Processing (STFAP) algorithm is derived, which allows channel separation without any interferences. Basically, STFAP forms frequency- and time-variant antenna beams, which follow the echo signals of each transmitted waveform individually. However, this method demands waveforms of certain structures, which are described and suitable waveform types are compared in detail. STFAP and other DBF-SAR techniques need very sharp antenna beams in elevation. In presence of unknown topography, when the assumed geometrical model of the Earth surface is complex, antenna pointing might be mismatched with the surface geometry. To handle this issue, it is suggested to apply an additional algorithm prior to DBF, which determines the angle of the incident echo signal on the antenna array. The algorithm, which is proposed in this dissertation, is based on the matrix pencil method and allows a highly accurate and signal-adaptive DBF in real-time. For an experimental verification of new imaging modes and STFAP, a groundbased MIMO-SAR demonstrator in X-band has been developed. The dissertation concludes with its description and promising experimental results, which proof that the suggested concepts have the potential to enhance the capabilities of state-of-the-art SAR sensors significantly.