SHARPEST: atmospheric turbulence characterization for future AO systems at the Subaru Telescope

Atmospheric turbulence profile plays an important role in designing and operating adaptive optics (AO) systems with multiple laser guide stars. To obtain representative free atmospheric profiles and resolved ground layer profiles for future AO systems at the Subaru Telescope, we are conducting the SHARPEST (Shack-Hartmann Atmospheric tuRbulence Profiling Experiment at the Subaru Telescope) project. In this project, we develop a turbulence profiler comprising two Shack-Hartmann (SH) sensors to observe a pair of bright stars through the Subaru Telescope with high spatial sampling by 2 cm subapertures. We perform two main analyses on the SH spot data: variance analysis on the spot scintillation for free atmospheric profiles, and on the spot slope for ground layer profiles. Through the three previous engineering observations, we establish a method to constrain the turbulence profile as well as the total seeing and the wind profile by analyzing data from the SH sensors. The free atmospheric profiles reconstructed by the two independent SH sensors show good agreement and are also consistent with simultaneous measurements by another profiler except for turbulence strength at ∼ 1 km, which might be explained by an overestimation problem of scintillation-based profilers. The wind profiles show good consistency with the direct measurements by a rawinsonde. The ground layer profile results, obtained by combining data from the two SH sensors, suggest that turbulence is concentrated in the range up to ∼ 50 m above the primary mirror. As a comparative measurement for the dome seeing, we are currently planning to install AIRFLOW, a small local turbulence sensor inside the dome.