Characterisation of the Optical Turbulence at Siding Spring

TL;DR

This study characterizes optical turbulence at Siding Spring Observatory, revealing dominant ground-layer turbulence, non-Kolmogorov behavior, and median seeing of 1.2" to inform adaptive optics performance predictions.

Contribution

It provides a detailed turbulence profile model based on SLODAR measurements, highlighting the dominance of ground-layer turbulence and its non-Kolmogorov nature.

Findings

Ground-layer turbulence accounts for up to 80% of total turbulence.

Turbulence exhibits non-Kolmogorov power law with index ~10/3.

Median atmospheric seeing is approximately 1.2 arcseconds.

Abstract

Measurements of the optical turbulence profile above Siding Spring Observatory were conducted during 2005 and 2006. This effort was largely motivated by the need to predict the statistical performance of adaptive optics at Siding Spring. The data were collected using a purpose-built instrument based on the slope-detection and ranging method (SLODAR) where observations of a bright double star are imaged by Shack-Hartmann taken with the Australian National University 24 inch and 40 inch telescopes. The analysis of the data yielded a model consisting of a handful of statistically prominent thin layers that are statistically separated into the ground layer (37.5, 250m) and the free atmosphere (1, 3, 6, 9, 13.5 km) for good (25%), typical (50%) and bad (25%) observing conditions. We found that ground-layer turbulence dominates the turbulence profile with up to 80% of the integrated turbulence below 500 m. The turbulence tends to be non-Kolmogorov, especially for the ground-layer with a power law index of $\beta \sim 10/3$. The mirror/dome seeing can be a significant fraction of the ground-layer turbulence. The median atmospheric seeing, is around 1.2", in agreement with observational reports.