Correlating SAR (CoSAR): Concept, performance analysis, and mission concepts

Synthetic Aperture Radar (SAR) systems construct the equivalent to a very long antenna array by coherently combining radar echoes of a scene acquired along the trajectory of a space- or airborne radar. A key underlying assumption, or requirement, is that the observed scene stays coherent during the acquisition. This is true for static scenes, in particular when the acquisition time is kept short. For decorrelating targets, the azimuth resolution achievable by a SAR system is limited by the coherence time of the targets, τ_coh, which limits the length of the synthetic aperture to the product of τ_coh and the azimuth velocity of the system. Typical cases where this can be an issue is for the observation of water surfaces, where the coherence times at microwave frequencies are typically well below 100 ms, which makes them short compared to the typically associated integration times.