An Optimal Imaging Time Interval Selection Technique for Marine Targets ISAR Imaging Based on Sea Dynamic Prior Information

Marine targets are usually involved in remarkably strong maneuvering motion due to sea wave disturbance, which will cause continual change of inverse synthetic aperture radar image projection plane (ISAR IPP). As a result, optimal imaging time interval (OITI) selection is indispensable to obtain well-focused ISAR images. Conventional OITI selection algorithms are entirely driven by echo signal, so strong noise has been always challenging the conventional methods in parameter estimation, and the algorithm accuracy is insufficient. Moreover, the analyses for echo signal in traditional methods cost a considerable number of computational loads, leading to low algorithm efficiency. In this paper, a novel OITI selection algorithm for marine targets is proposed via sea dynamic prior information (SDPI) (such as sea state, ship navigation speed, and wave direction angle) instead of echo signal. In the proposed technique, the coupling mechanism between time-varying 3D rotational motion of marine targets (roll, pitch, and yaw) and SDPI can be inferred integrating with hydrodynamics. Based on this, the effective rotational vectors (ERVs) of marine targets relative to radar line of sight (RLOS) can be deduced from the combination of rotational motion and translational motion. It is worth noting that the ERV is an accurate result with the accommodation of complex SDPI rather than an approximate value obtained from the echo signal. By means of the ERV and maximum contrast criterion, the optimal imaging instant (OII) and optimal imaging duration (OID) can be accurately determined, respectively. Without huge computational complexity, the proposed algorithm provides good robustness and high accuracy. Extensive experiments based on electromagnetic simulated data are provided to demonstrate the effectiveness of the proposed algorithm.