Measurement of atmospheric coherence length of optical propagation along long distance path

Atmospheric coherence length over a nearly horizontal and 3.95 km path was experimental studied by the large aperture scintillation and differential image motion measure angle-of-arrival fluctuation methods. For two direction (up and down) of the same path, the experiment results show that the correlation coefficient of the large aperture scintillation method is 0.94, while the correlation coefficient of differential image motion measure angle-of-arrival fluctuation method is 0.79. Analysis of path weight function reveals that scintillation is most sensitive to the eddy in the center of the path and its path weight function is symmetrical in the measured path; however, DIMM is most sensitive to the eddy near the receiver and its path weight function is increased monotonically along with measured path from transmitter to receiver. Therefore, the scintillation maybe more appropriate for measuring turbulent effects when light propagate along long distance path whose turbulence intensity distribution is indistinct.