Coherent 1-microm lidar measurements of atmospheric-turbulence-induced spatial decorrelation using a multielement heterodyne detector array.

We have employed a coherent 1-microm Nd:YAG lidar system to measure directly, for the first time to our knowledge, the reduced spatial coherence length, p(0), of the lidar returns caused by atmospheric turbulence. Our experiments were conducted by using a 2 x 2 heterodyne detector array, which permitted real-time spatial correlation measurements of the lidar returns at two different detector spacings. The spatial correlation coefficients and spatial coherence length of the lidar returns from a hard target weremeasured during a day-to-night time period when the atmospheric turbulence parameter, C(n)(2), was measured to vary from 2 x 10(-13) to 2 x 10(-14) m(-1/3). These directly measured values of p(0) as a function of C(n)(2) were found to be in good agreement with theoretical predictions.