Stellar scintillation in the short exposure regime and atmospheric coherence time evaluation

Sternberg Astronomical Institute, Universitetskij pr-t, 13, 119992 Moscow, Russia
e-mail: victor@sai.msu.ru

Received: 20 January 2011
Accepted: 24 March 2011

Abstract

Aims. Accurately measuring the atmospheric coherence time is still a significant 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 τ₀.

Methods. 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 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.

Results. The expressions for the mean wind speeds 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 τ₀ without the need of empirical calibration. The verification of the method based on real measurements of the resulting τ₀ agree well with independent methods.