Polychromatic Time Domain Reconstruction Approach for Along-track Multistatic SAR Constellations with Varying PRI

Next-generation spaceborne Synthetic Aperture Radar (SAR) systems aim at very high resolution imaging over wide swaths in the order of hundreds of kilometers. One viable realization of such a concept is distributed SARs with along-track baselines operated under the Nyquist frequency. Undersampled received data stack needs to be reconstructed to obtain azimuth-ambiguity free data on a regular sampling grid. On the other hand, very high-resolution distributed SAR system requires very precise orbit control to avoid sampling instabilities in along-track and phase error due to the topographic sensitivity. Both time and Doppler domain reconstruction methods in the literature perform well in case of uniform and nonuniform sampling conditions. However, highly nonuniform sampling and coinciding sampling result in severe signal-to-noise ratio degradation or impossibility to recover the entire Doppler bandwidth. Depending on the frequency band, even a small cross-track baseline in the order of few meters may result in high phase errors over mountainous terrain. In this paper, we analysed the impact of the varying pulse repetition interval (PRI) on the azimuth sampling condition and proposed two time-domain polychromatic reconstruction methods suitable for multistatic SAR constellations with varying PRI.