Retrieval of Ship Radial Velocity From Single-Channel Complex-Valued Spaceborne SAR Imagery

This article proposes two different techniques to estimate the radial velocity component in complex-valued single-channel space-based synthetic aperture radar (SAR) systems for ships on the open ocean in cases where ship wakes or other features are not observable. While the first technique is based on the well-known Doppler centroid anomaly detection method developed for improved SAR processing, the second novel technique exploits the difference between the azimuth or Doppler ambiguities on either side of the ship image caused by a radial motion. Measuring either the ambiguity shift or the intensity ratio and comparing it with the theoretically expected values permits inferring an estimate of the radial velocity component. Estimation results for both techniques are compared with the Cramér–Rao bound (CRB) and the accurate benchmark estimator along-track interferometric (ATI). Although not as accurate as ATI, it is demonstrated that useful velocity information can be deduced, which is currently not available on almost all existing space-based SAR systems.