Development of Solar scintillometers and Lunar scintillometers for profiling the near-ground turbulence

Solar Scintillometer (SoSci) and Lunar Scintillometer (LuSci) can efficiently assess the near-ground optical turbulence, which are crucial characteristic parameters for astronomical observatory sites. This paper presents the development and comparative analysis of two side-by-side SoSci / LuSci systems, aimed at determining the accuracy of turbulence data and its dependence on instrument calibration. Experiments conducted at both the park area of Nanjing Institute of Astronomical Optics & Technology and the Xuyi Observation Station of Purple Mountain Observatory in China demonstrate that atmospheric turbulence primarily affects solar or lunar flux fluctuations in the low-frequency range. The differences in the refractive index structure constant values obtained from the scintillometers with the identical configurations are minimal at the pivot points. Similarly, there are negligible differences in turbulence integrals, seeing values, and atmospheric coherence length values between them. Theoretical analysis and numerical computation of the weight function indicate that employing a normalized disk instead of the actual sun or moon image will lead the scintillometer to overestimate the turbulence near the ground. If the out scale of turbulence considered for data processing is larger or smaller than the actual value, the scintillometer will theoretically underestimate or overestimate high-altitude turbulence, respectively. However, the out scale of turbulence has minimal impact on the scintillometer's ability to assess low-altitude turbulence, making it reliable for profiling ground layer turbulence. Furthermore, the temporal trends observed in the seeing measurements via the Lunar Scintillometer are in good agreement with those from the Differential Image Motion Monitor, indicating that ground layer turbulence dominates the total turbulence.