Optical measurement of the inner scale of turbulence

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Abstract
Presents a method for the determination of the path-averaged value of the inner scale of atmospheric turbulence, l0, using an optical scintillometric method. The proposed method involves the measurement of the bichromatic correlation of two laser beams of different wavelengths propagating in overlapping paths. Results obtained using this technique are compared with the ratio of the log-amplitude variances of the two laser beams and with l0 values derived from vertical wind velocity fluctuation measurements. The results of the correlation method agree well with theory based upon Hill's refractive index spectrum. Results obtained by the ratio of variances match those obtained by the correlation technique after correction for the refractive index dispersion due to humidity fluctuations. These two methods can be used jointly for the simultaneous determination of l0, CT2 and CQ2.