Abstract
In this paper, we present a detailed analysis on the performance degradation of inverse synthetic aperture radar (ISAR) imagery with the polar format algorithm (PFA) due to the inaccurate rotation center. And a novel algorithm is developed to estimate the rotation center for ISAR targets to overcome the degradation. In real ISAR scenarios, the real rotation center shift is usually not coincided with the gravity center of the high-resolution range profile (HRRP), due to the data-driven translational motion compensation. Because of the imprecise information of rotation center, PFA image yields model errors and severe blurring in the cross-range direction. To tackle this problem, an improved PFA based on integrated cubic phase function (ICPF) is proposed. In the method, the rotation center in the slant range is estimated firstly by ICPF, and the signal is shifted accordingly. Finally, the standard PFA algorithm can be carried out straightforwardly. With the proposed method, wide-angle ISAR imagery of non-cooperative targets can be achieved by PFA with improved focus quality. Simulation and real-data experiments confirm the effectiveness of the proposal.
Highlights
Inverse synthetic aperture radar (ISAR) can generate two-dimensional (2D) images for a non-cooperative moving target, which has wide military and civil applications
3.1 The performance degradation of polar format algorithm (PFA) when Δr ≠ 0 According to Equations (8 to 10), one notes that when the rotation center (RC) locates at the cell of the reference point (RP), the phase term of the dechirped signals can be expressed in the polar format
With the proposed integrated cubic phase function (ICPF) estimation of RC, the high-resolution range profile (HRRP) of shifted signals are shown in Figure 13d and the image with PFA is shown in Figure 13f, where compensation of both rotation induced migration through resolution cells (MTRC) and time-varying Doppler is achieved in an optimal manner
Summary
Inverse synthetic aperture radar (ISAR) can generate two-dimensional (2D) images for a non-cooperative moving target, which has wide military (e.g., military target classification and recognition) and civil (e.g., civil aircraft control) applications. [16], a method was proposed to estimate the rotation angle and center using a correlation-based function. It needs careful choosing and tracking of two scattering centers in the range-compressed phase history, which may be difficult for high-resolution ISAR. In ref [17], a method based on a concept of rotation correlation is proposed, which searches the rotation parameters by iteratively interpolating the RD image. A method based on integrated cubic phase function (ICPF) is proposed for PFA to eliminate the effect of the disturbance system and the rotation center can be derived precisely.
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