A new method for measuring the outer scale of atmospheric turbulence

A method, based on the correlation functions of the wandering (lateral fluctuations) of two separated thin parallel laser beams propagating through the atmosphere, is proposed for measuring the outer scale of atmospheric turbulence. The method utilizes the ratio between the correlation functions of the wandering in two perpendicular planes. A simple relationship to obtain the outer scale from the measured correlation functions is established for a particular model of turbulence, the modified von Karman model. The method is validated by experimental data both in the laboratory and in the open air. To this purpose special measurements, which were conducted during an outdoor measurements campaign in 2004, are analysed. An instantaneous value of the outer scale can be obtained accurately. The results show that the size of outer scale of atmospheric turbulence changes very rapidly with time and that the proposed method can be applied in real atmospheric conditions.