Effect of atmospheric turbulence anisoplanatism on LEO satellite-to-ground laser communications links.

Low earth orbit (LEO) satellite-to-ground laser communications (SGLC) links experience continuous variation in both the propagation paths and the atmospheric turbulence due to the satellite's orbital motion. This paper presents an atmospheric turbulence measurement system (ATMS) capable of simultaneously monitoring multiple optical paths to characterize turbulence parameters and validate anisoplanatism effects. The system evaluates atmospheric turbulence by analyzing both scintillation in light intensity and centroid drift in stellar speckle images. To enhance the accuracy of centroid positioning, a sub-pixel interpolation algorithm based on Zernike moments is proposed, further enhanced through a gray-gradient-weighted strategy. Experimental results from LEO-SGLC scenarios indicate that single-path measurements are consistent with the expected statistical properties of atmospheric turbulence. However, low correlation coefficients between different measurement paths were 0.0151 and 0.1667, respectively, demonstrating significant anisoplanatism. These findings underscore the critical role of multi-path observations in identifying minute scale optimal communication windows, thereby enhancing the stability and reliability of the LEO-SGLC link.