Autofocus motion compensation method of airborne ultra-high resolution SAR (Synthetic Aperture Radar) back projection image

Abstract

The invention discloses an autofocus motion compensation method of an airborne ultra-high resolution SAR (Synthetic Aperture Radar) back projection image. The phase error introduced by the deviation of a flight path cannot be fully compensated through a radar platform motion sensor under the condition of high resolution and accordingly the image focusing quality is affected. The target defocusing can exist along different inclined directions in the image reconstruction by a back projection algorithm, the target distance migration cannot be strictly limited within a distance resolution cell, and the traditional autofocus processing fails. The correction is performed on the sub-bandwidth autofocus motion compensation processing of an imaging grid; the data collection is performed on the inclined plane after the correction for image reconstruction and the space-variant characteristics of the target defocus direction is completely removed; the sub-bandwidth decomposition is performed on back projection processing data and the phase gradient autofocus and splicing is performed to obtain a refocused image. Compared with the existing algorithm, the high-order motion phase error is considered and the effective compensation of the phase error in the image reconstruction by the back projection algorithm is implemented.

Description

technical field [0001] The invention relates to the field of radar technology, in particular to a self-focusing motion compensation method for an airborne ultra-high resolution SAR back-projection image. Background technique [0002] Back projection (BP) algorithm is a classic time-domain imaging method of Synthetic Aperture Radar (SAR). In BP processing, the SAR echo data is obtained through space-variant back-projection and azimuth matched filtering, and the calculation load is very large. In practical applications, the fast back-projection method is usually used instead of BP to achieve efficient focused imaging of SAR data. In the present invention, BP and various fast back-projection methods are collectively referred to as back-projection algorithms. The back-projection algorithm has high precision and can achieve good focus of SAR data under any known track conditions. It has been widely used in large squint, nonlinear aperture, dual (multi-base) and new system SAR c...

AI Technical Summary

Problems solved by technology

However, the existing autofocus methods do not take into account the high-frequency motion phase error; the BP image autofocus processing based on the principle of maximizing image clarity is computationally intensive and extremely complex; in addition, the geometric space-based decomposition autofocus processing need to rely on high-precision motion measurement system

In the existing methods, considering the use of polar coordinate format grids for projection imaging, it can only eliminate the spatial variation characteristics of the target defocus in the central part of the scene under certain conditions; in addition, the sub-aperture self-focusing based on FFBP does not consider the high-order phase error, and difficult to apply under high strabismus conditions

Therefore, under the condition of airborne ultra-high resolution in the prior art, there are still defects in the self-focusing motion compensation of the back-projection reconstructed image

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