Daytime turbulence strength profile measurement at Kodaikanal Observatory

TL;DR

This paper presents the first daytime turbulence strength profile measurements at Kodaikanal Observatory using innovative methods, identifying a strong turbulence layer at 3 km and validating a low-cost measurement setup.

Contribution

It introduces two novel methods for daytime turbulence profiling and demonstrates their effectiveness at Kodaikanal Observatory.

Findings

Identification of a strong turbulence layer at 3 km altitude.

Validation of a low-cost turbulence measurement setup.

Measured turbulence parameters consistent with existing models and previous observations.

Abstract

The Indian Institute of Astrophysics (IIA) is developing a Multi-Conjugate Adaptive Optics (MCAO) system for the Kodaikanal Tower Telescope (KTT). In this context, we have measured the daytime turbulence strength profile at the Kodaikanal Observatory. The first method based on wavefront sensor (WFS) images, called S-DIMM+ (Solar-Differential Image Motion Monitor+), was used to estimate the higher altitude turbulence up to a height of 5 - 6 km. The second method used balloon-borne temperature sensors to measure the near-Earth turbulence up to 350 m. We also carried out simulations to validate the performance of our system. We report the first-ever daytime turbulence strength profile measurements at the observatory. We have identified the presence of a strong turbulence layer about 3 km above the observatory. The measured near-Earth turbulence matches the trend that is expected from the model for daytime component of turbulence and gives an integrated $r_0$ of about 4 cm at 500 nm. This is consistent with earlier seeing measurements. This shows that a low-cost setup with a small telescope and a simple array of temperature sensors can be used for estimating the turbulence strength profile at the site.