Multistatic synthetic aperture radar autofocus for back projection imaging of a moving target

Synthetic Aperture Radar (SAR) plays a vital role in the surveillance of terrestrial and maritime targets, which are commonly in motion. As such, the ability to perform accurate real‐time focusing and localisation on moving targets, particularly those moving with complex motion, is desired. Many existing autofocus algorithms struggle to achieve this and rely on sub‐aperture processing of SAR data to estimate and compensate for phase errors attributed to unknown target motion. This paper presents a new metric‐based autofocus approach, called Localised Threshold Sharpness (LTS), which employs multistatic SAR data to localise and focus a target moving with up to six degrees of freedom motion on a real‐time, pulse‐by‐pulse basis. The algorithm is verified with experimental data, and its performance is compared against the performance of an existing measure of image sharpness suitable for pulse‐by‐pulse autofocusing, namely the intensity‐squared metric, with varying levels of added noise. Normalised cross‐correlation results demonstrate a resemblance of at least 80% between Multistatic SAR images focused via LTS autofocus and Multistatic SAR images ideally focused using target motion knowledge for signal‐to‐noise ratios above 3 dB.