Integration of Imaging and Recognition for Marine Targets in Fast-Changing Attitudes With Multistation Wideband Radars

Affected by the ocean environments, such as sea waves and wind, the marine targets perform periodic three-dimensional swaying motion (3D-SM) (roll, pitch, and yaw), which leads to the characteristic of fast-changing attitudes in the process of wideband measurement. It challenges the conventional inverse synthetic aperture radar (ISAR) imaging techniques. In addition, the available studies on ship target recognition based on ISAR images mainly focus on the classification of military and civil ships as well as large-, medium-, and small-sized ships, while the recognition of the specific types of ship targets has been underresearched. To address the above problems, this article proposes a processing framework for marine targets in fast-changing attitudes to achieve the integration of imaging and recognition with multistation wideband radars. For ISAR imaging of complex maneuvering ships in fast-changing attitudes, there is spatial–time-variant characteristic (STVC) of rotational motion relative to radars. Hence, a modified grasshopper optimization algorithm-based fine phase autofocus algorithm is proposed to eliminate the complex spatial–time-variant phase errors caused by STVC by solving the maximum image contrast optimization. With regard to target recognition, a two-stage estimation method based on sequence ISAR imaging of multistation wideband radars is developed to obtain the instantaneous attitudes, geometric sizes, and periods of 3D-SM. Moreover, drawing on the knowledge of hydrodynamics, the typical recognition feature parameters (TRFP) of length between perpendiculars, width, draft, and metacentric height of ships can be further estimated by periods of 3D-SM, which lends crucial data support for the recognition of ship target type. The combination of the fine imaging and TRFP estimation algorithms thus makes it possible to integrate the imaging and recognition of marine targets in fast-changing attitudes. Extensive experiments with various types of ships in different motion states are provided to verify the feasibility and effectiveness of the proposed algorithm.