Atmospheric turbulence profiling using multiple laser star wavefront sensors

TL;DR

This paper presents advanced methods for atmospheric turbulence profiling using multiple laser guide star wavefront sensors in the Gemini MCAO system, including adaptations of SLODAR and wind profiling techniques for multi-layer atmospheric analysis.

Contribution

It introduces a novel adaptation of the SLODAR method for close-loop, multi laser guide star systems and demonstrates turbulence profiling for up to 16 layers from 0 to 19 km altitude.

Findings

Characterized turbulence up to 16 layers from 0 to 19 km.

Validated wind profiling as a tool for turbulence and system verification.

Addressed challenges like Rayleigh scattering and centroid gain variations.

Abstract

This paper describes the data preprocessing and reduction methods together with SLODAR analysis and wind profiling techniques for GeMS: the Gemini MCAO System. The wavefront gradient measurements of the five GeMS's Shack-Hartmann sensors, each one pointing to a laser guide star, are combined with the DM commands sent to three deformable mirrors optically conjugated at 0, 4.5 and 9 km in order to reconstruct pseudo-open loop slopes. These pseudo-open loop slopes are then used to reconstruct atmospheric turbulence profiles, based on the SLODAR and wind-profiling methods. We introduce the SLODAR method, and how it has been adapted to work in a close-loop, multi Laser Guide Star system. We show that our method allows characterizing the turbulence of up to 16 layers for altitudes spanning from 0 to 19 km. The data preprocessing and reduction methods are described, and results obtained from observations made in 2011 are presented. The wind profiling analysis is shown to be a powerful technique not only for characterizing the turbulence intensity, wind direction and speed, but also as it can provide a verification tool for SLODAR results. Finally, problems such as fratricide effect in multiple laser system due to Rayleigh scattering, centroid gain variations, and limitations of the method are also addressed.