Phase compensation of SAL imaging combining Rayleigh LGS with PGA in strong turbulence

High imaging resolution can be achieved by using synthetic aperture ladar (SAL) with laser radiation source. The destruction of the signal phase information caused by atmospheric turbulence makes the optical heterodyne detection efficiency reduce. Therefore the imaging performance of SAL degraded seriously. The study on the influence of atmospheric turbulence on SAL imaging is of great significance and an effective compensation method of image is necessary to be found. Research shows that conventional phase gradient autofocus (PGA) algorithm has some improvement on SAL imaging only in weak turbulence. The mixed phase compensation method combining Rayleigh laser guide star (LGS) with PGA algorithm is presented based on the real-time detection of optical wavefront phase distortion with Rayleigh LGS and the phase compensation method of the SAL images. The phase distortion caused by different turbulence intensities with von Karman spectrum is estimated with Rayleigh LGS. SAL echo signals are compensated with the estimated phase and the PGA algorithm is implemented in the final imaging data. The results show that significant improvements of the SAL images in moderate turbulence are obtained and the images can be identified basically by using the mixed phase compensation method in strong turbulence. The focusing effect of the SAL images is improved effectively, and a higher SAL resolution is gained in azimuth. In addition, the research of SAL imaging compensation in atmospheric turbulence in a slant path is carried out for the first time, which is of great significance to the practical application of SAL.

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