Continuous 24-hour Shack-Hartmann optical turbulence profiling on a small telescope.

Abstract

Atmospheric optical turbulence monitoring has been used for site selection and operation scheduling at observatories for decades, and is a critical element in the operational package for upcoming 20-40 m class telescopes. Furthermore it is a key validation method for adaptive optics systems. Continuous, 24-hour optical turbulence monitoring is a novel capability with a number of high-impact applications in astronomy, solar astronomy, optical turbulence forecasting and free space optical communications. The subject of this thesis is the Shack-Hartmann Image Motion Monitor (SHIMM), the first continuous 24-hour optical turbulence monitor. The instrument uses short-wave infrared observations of bright stars with a Shack-Hartmann wavefront sensor and small telescope to measure optical turbulence parameters and a low-resolution Cn^2 profile. Combined slope and intensity measurements from the Shack-Hartmann sensor are used to characterise the turbulence profile, and methods are validated through Monte Carlo simulations. The opto-mechanical design consists primarily of commercially-available components and is portable on a 28 cm telescope. The transmission spectrum is estimated and validated, finding a central wavelength of approximately 1280 nm. Using the simulation results, the maximum target star magnitude is found to be 0.07 in the J band and target availability to be sufficient for continuous measurements. Finally, on-sky results are presented for two sites: Paranal observatory and Barcelona. At the former, the SHIMM is found to agree well with existing turbulence monitoring instruments at the site. The latter is a permanent urban monitoring station, and early site monitoring are discussed indicating strong turbulence and that adaptive optics would be advantageous for a potential ground station.