Measurement of turbulence profile from defocused ring images

TL;DR

This paper introduces a novel, low-cost turbulence monitoring method using defocused star images to measure atmospheric turbulence profiles, total seeing, and time constants, validated through simulations and prototype testing.

Contribution

It presents a new turbulence measurement technique based on analyzing ring-like images, enabling low-cost, portable site testing and improvements over existing monitors.

Findings

Successfully tested with a 0.13-m prototype on the sky.

Accurately measures turbulence profile, seeing, and atmospheric time constant.

Provides correction methods for exposure time and scintillation effects.

Abstract

A defocused image of a bright single star in a small telescope contains rich information on the optical turbulence, i.e. the seeing. The concept of a novel turbulence monitor based on recording sequences of ring-like intrafocal images and their analysis is presented. It can be implemented using standard inexpensive telescopes and cameras. Statistics of intensity fluctuations in the rings and their radial motion allow measurement of the low-resolution turbulence profile, the total seeing, and the atmospheric time constant. The algorithm of processing the images and extracting the turbulence parameters is developed and extensively tested by numerical simulation. Prescriptions to correct for finite exposure time and partially saturated scintillation are given. A prototype instrument with a 0.13-m aperture was tested on the sky. The RINGSS (Ring-Image Next Generation Scintillation Sensor) can be used as a portable turbulence monitor for site testing and as an upgrade of existing seeing monitors.