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.
Based on the theory of optical wave propagation in the slant path and the ITU-R turbulence structure constant model
which is dependent on altitude, the on-axis scintillation index of the flat-topped Gaussian beam at the receiver plane in
slant path turbulence was given by using Kolmogorov atmospheric turbulence power spectrum model. The influences of
the link altitudes, atmospheric refractive index structure constant C0 at the ground，the source size and the beam order on scintillation index of the flat-topped Gaussian beam are discussed in detail. The result shows that the scintillation index
increased first and then decreased with the increase of the beam order. The advantage of a flat-topped Gaussian beam
over a single Gaussian beam is restricted to small source sizes, which is consistent with the case of the horizontal path.
To find the average bit error rate under weak slant path turbulence, the log-normal distribution model of the intensity
fluctuation was used. The influence of beam order and source size on BER was discussed. The result indicates that the
smaller sized flat-topped Gaussian beam will bring average bit error rate advantage over the same size Gaussian beam.
Our results correctly reduce to the result of the horizontal path with atmospheric structure constant fixed.