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Accurately measuring the atmospheric coherence time is still an importantproblem despite a variety of applicable methods. The Multi-aperturescintillation sensor (MASS) designed for the vertical profiling of opticalturbulence, also provides a measurements of coherence time, but its resultswere found to be biased. Hence there is a need for a more robust method todetermine $\tau_0$. The effect of smoothing the stellar scintillation by afinite exposure of the detector is considered. The short exposure regime isdescribed and its limits are defined. The re-analysis of previous measurementswith the MASS is performed in order to test the applicability of this approachin real data processing. It is shown that most of the actual measurementssatisfy the criteria of short exposures. The expressions for the mean windspeeds $\bar V_2$ in the free atmosphere from the measurement of thescintillation indices are derived for this regime. These values provide anestimate of the atmospheric coherence time $\tau_0$ without the need ofempirical calibration. The verification of the method based on realmeasurements of the resulting $\tau_0$ are in good agreement with independentmethods.

Stellar scintillation in short exposure regime and atmospheric coherence time evaluation