Stellar scintillation in short exposure regime and atmospheric coherence time evaluation

TL;DR

This paper presents a new method to accurately measure atmospheric coherence time using stellar scintillation in the short exposure regime, reducing bias and eliminating the need for empirical calibration.

Contribution

It introduces a robust approach for determining atmospheric coherence time from MASS measurements by analyzing short exposure scintillation data, improving accuracy over previous methods.

Findings

Most measurements satisfy short exposure criteria

Derived expressions for mean wind speed in the free atmosphere

Good agreement with independent coherence time measurements

Abstract

Accurately measuring the atmospheric coherence time is still an important problem despite a variety of applicable methods. The Multi-aperture scintillation sensor (MASS) designed for the vertical profiling of optical turbulence, also provides a measurements of coherence time, but its results were found to be biased. Hence there is a need for a more robust method to determine $\tau_0$. The effect of smoothing the stellar scintillation by a finite exposure of the detector is considered. The short exposure regime is described and its limits are defined. The re-analysis of previous measurements with the MASS is performed in order to test the applicability of this approach in real data processing. It is shown that most of the actual measurements satisfy the criteria of short exposures. The expressions for the mean wind speeds $\bar V_2$ in the free atmosphere from the measurement of the scintillation indices are derived for this regime. These values provide an estimate of the atmospheric coherence time $\tau_0$ without the need of empirical calibration. The verification of the method based on real measurements of the resulting $\tau_0$ are in good agreement with independent methods.