Measurement of atmospheric coherent length by four-aperture differential image motion method

A new kind of angle of arrival fluctuation measurement by differential image motion method(DIMM) is introduced. Fried parameter of two orthogonal base line directions can be obtained by angle of arrival fluctuation variance. The experiment results of horizontal propagation in the real atmosphere show that there are apparent differences between the four coherent length values, and the atmospheric turbulence is anisotropic. This characterization should be taken into account in applications. At least one of the measurement values of four directions is necessary for the analysis and study of determining the atmospheric coherence length.