Integration of High-Order Motion Compensation and 2-D Scaling for Maneuvering Target Bistatic ISAR Imaging

It is challenging to achieve bistatic inverse synthetic aperture radar (Bi-ISAR) imaging and scaling for maneuvering targets. In the Bi-ISAR system, high-order translational and spatial variant (SV) rotational motion errors induced by the target's maneuvering characteristics and time-varying bistatic angle would severely blur the imaging result. Moreover, both range and cross-range scaling (2-D scaling) are needed to exploit the size information of the target in practical applications. By parametric global modeling and extracting the coupling relationship between the target's rotational motion and time-varying bistatic angle, this article presents a new Bi-ISAR imaging framework to achieve the integration of high-order motion compensation and 2-D scaling (IHOMC-2S) for maneuvering targets. First, a multidimensional motion errors signal model is developed. Based on the established parametric global model, a joint high-order translational motion compensation and SV autofocus method (JHTSVA) is presented via parametric minimum entropy optimization with the quasi-Newton solver. Then, with the estimated optimal parameters, the effective rotational velocity (ERV) and distortion coefficient can be estimated simultaneously by solving a 1-D unconstrained optimization problem. In addition, in order to successfully perform the 2-D scaling, a data-driven initial bistatic angle estimation method based on the linked feature scatterers is given. It is worth noting that the linear geometric distortion must be corrected before 2-D scaling, otherwise the sheared Bi-ISAR image may lead to an unreliable target recognition result. Finally, underpinned by the efficient and robust approach, IHOMC-2S can achieve high-resolution Bi-ISAR imaging and scaling for maneuvering targets avoiding the selection of prominent scatterers. Several experiments confirm the feasibility and robustness of the proposed algorithm.