Estimation of Vessel Rotational Motion From Satellite SAR Using Target Motion Phase Refocusing

This study quantitatively measured vessel rotational motion from satellite SAR data using a target motion phase refocusing function. In contrast to horizontal linear motion of vessel, vessel rotational motion caused by ocean wave force was not able to be monitored from AIS information and accordingly rarely studied. Nevertheless, extensive vessel rotational motion was directly related to vessel motion hazard and potential of maritime accident, which was required to be measured in order to thoroughly analyze vessel movement. A target motion SAR phase refocusing function was proposed, which effectively measured vessel velocity, acceleration, and accordingly its rotational motion, conventionally named as yawing, pitching, and rolling motion. A total of 29 vessels whose velocity exceeding 1 m/s were selected from three different satellite SAR images and analyzed using the target motion SAR phase refocusing function. It precisely measured vessel velocity and acceleration, and subsequently derived horizontal and vertical vessel angular accelerations, which reorganized vessel yawing, pitching, and rolling motion. When compared with AIS-driven motion, estimated azimuth velocity and horizontally projected range acceleration respectively derived RMSE offset of 0.49 m/s and 0.0032 m/s2. Moreover, the proposed phase refocusing function outperformed the conventional SAR phase focusing algorithms in aspect of focusing performance. As the measurement of the vessel rotational motion using the proposed refocusing function was presented, it can be practically applied to monitoring vessel motion hazard in ocean using satellite SAR data.