Turbulence profiler and seeing monitor for laser guide star adaptive optics

摘要

We have developed a system for real-time monitoring of the optical turbulence altitude profile in the atmosphere above large telescopes. A high order Shack-Hartmann wavefront sensor is used to observe bright binary stars, and the turbulence profile is recovered from a cross-correlation of the measured wavefront slopes. This method is referred to as SLODAR (SLOpe Detection And Ranging), by analogy with the well-known SCIDAR binary star scintillation profiling technique. SLODAR can be implemented using relatively simple and inexpensive hardware. The monitor described here is based on a commercially available unintensified Firewire digital video camera. The system has been installed at the 4.2m William Herschel telescope in La Palma and will be used to support observations with adaptive optical correction at the telescope. The turbulence data will allow optimisation of range-gate altitudes for Rayleigh laser beacons, deformable mirror conjugation altitudes and other AO system parameters, as well as characterisation of the AO corrected point spread function for anisoplanatism. The system will also provide statistical site characterisation data to permit accurate modeling of future AO instruments.