SAR retrieval of a ship vertical profile from her roll and pitch motion

Abstract:
SAR imaging of a running ship classically entails location aberration due to across-track component of the ship velocity as well as azimuth defocusing due to the along-track component. Inverse SAR approach allows retrieval of relative target rotation rate thus compensating its along-track velocity component. This approach assumes that the sensor motion with respect to the ship frame is confined to the imaging plane. With increasing resolution, integration time increases beyond the period of typical ship pitch and roll motion, thus significantly deviates from a plane the sensor motion with respect to the ship frame. Autofocus by multilateration on several tie-points on the ship frame allows to retrieve accurate 3D sensor relative trajectory. Ship image focusing becomes strongly height-dependent due to trajectory undulation. Height of point-like echoes can be determined by comparing sharpness of a set images focused on a range of height. The height documented SAR images when projected on a vertical plane yields profile views of target useful for ship identification.