Abstract
Moving ship refocusing is challenging because the target motion parameters are unknown. Moreover, moving ships in squint synthetic aperture radar (SAR) images obtained by the back-projection (BP) algorithm usually suffer from geometric deformation and spectrum winding. Therefore, a spectrum-orthogonalization algorithm that refocuses moving ships in squint SAR images is presented. First, “squint minimization” is introduced to correct the spectrum by two spectrum compression functions: one to align the spectrum centers and another to translate the inclined spectrum into orthogonalized form. Then, the precise analytic function of the two-dimensional (2D) wavenumber spectrum is derived to obtain the phase error. Finally, motion compensation is performed in the two-dimensional wavenumber domain after the motion parameter is estimated by maximizing the image sharpness. This method has low computational complexity because it lacks interpolation and can be implemented by the inverse fast Fourier translation (IFFT) and fast Fourier translation (FFT). Processing results of simulation experiments and the GaoFen-3 squint SAR data validate the effectiveness of this method.
Highlights
Range Direction ship target obtained via the BP algorithm; (c) 2-D wavenumber spectrum of the image after the squint minimization process; process; (d) The image after squint minimization
Real experimental data recorded by the GaoFen-3 satellite were obtained to assess the performance of the presented refocusing method
A C-band (5.4 GHz) synthetic aperture radar (SAR) was installed on the GaoFen-3 satellite launched by China in August 2016 [35,36,37,38,39]
Summary
As a time-domain algorithm, the BP algorithm [11,12,13,14,15,16,17] is widely used in squint SAR imaging because it offers, e.g., more precise compensation to curved trajectories and lower computer memory demand [18] Since moving ship squint SAR images based on the BP algorithm usually suffer from geometric deformation and smearing, target detection and classification become considerably difficult.
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