Ship target ISAR imaging method based on fractional Fourier transform

Abstract

The invention provides a ship target ISAR imaging method based on fractional Fourier transform. The ship target ISAR imaging method comprises the steps of: acquiring a radar echo signal of a scattering point of a ship target in each distance unit; modeling the acquired radar echo signals in the distance units into multi-component secondary frequency modulation signals through pulse compression andmotion compensation; determining estimated parameters of scattering point echo signals in the distance units according to the secondary frequency modulation signals; updating radar echo signals in the distance units by adopting the estimated parameters of the scattering point echo signals in the distance units; and acquiring an ISAR image of a ship target by utilizing the updated radar echo signals. The ship target ISAR imaging method adopts a symmetrical correlation function, fractional Fourier transform and multi-product processing for the radar echo signals in sequence, avoids the couplingof time and time delay, estimates a quadratic term phase coefficient and a cubic term phase coefficient with high precision, adopts a range-instantaneous-Doppler imaging technology combining with parameter estimation, and obtains a high-quality and high-precision ISAR image of a moving target.

Description

technical field [0001] The invention relates to microwave imaging technology, in particular to a fractional-order Fourier transform-based ISAR imaging method for ship targets. Background technique [0002] Synthetic Aperture Radar (SAR) is the most common imaging radar, which is usually installed on moving platforms such as aircrafts and satellites, and is used to image delicate targets, that is, to the ground. Its essence is to synthesize a huge and effective antenna aperture equivalently in the azimuth direction through the relative motion between the radar and the target, thereby breaking through the limitation of the radar's real aperture antenna on the azimuth resolution, and making the radar imaging technology move towards A new level. Inverse Synthetic Aperture Radar (ISAR) is another radar imaging technology developed on the basis of SAR, aiming at solving the imaging problem of moving targets. ISAR is mostly placed in a fixed position to image moving targets, main...

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Problems solved by technology

In the case of complex sea conditions, the movement of the ship target is also complex, the three-dimensional rotation of the target is very serious, and the time-varying Doppler frequency is even more irregular. At this time, modeling the echo signal as an LFM signal is no longer sufficient. How to accurately estimate the various parameters of the signal is an urgent problem to be solved according to the needs of the actual situation

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