The ground-layer turbulence evaluation with low-layer SCIDAR and Lunar scintillometer

Ground layer atmospheric turbulence significantly affects the performance of ground-based large aperture optical telescopes and the design of associated adaptive optics systems. This paper conducts a comparative analysis of the Low-Layer SCIDAR (LOLAS) and Lunar Scintillometer (LuSci) techniques for characterizing turbulence profiles at the ground layer. A testing campaign took place at the Xuyi Observation Station of Purple Mountain Observatory in China during October 2023. The paper presents ground layer turbulence profiles simultaneously obtained by LOLAS and LuSci, revealing a consist distribution. The average height of various percentiles of ground layer strength, as measured by both instruments, demonstrates a high degree of agreement. Comparison of integrated seeing at different altitudes (50m, 100m, 150m, 200m, and 250m) from the ground exhibit a strong agreement, with LuSci recording approximately 0.3′′ smaller values compared to LOLAS. LOLAS tends to underestimate seeing with prolonged exposure times. It is noted that approximately 75% of the ground layer (0-250 meters) turbulence strength originates below 50 meters. These methods can be directly used for site-testing for the proposed Chinese Large Optical / Infrared Telescope.