Optical anemometry based on the temporal cross-correlation of angle-of-arrival fluctuations obtained from spatially separated light sources

For two optical waves propagating through the turbulent atmosphere, the temporal cross-correlation of their angle-of-arrival (AOA) fluctuations contains information regarding the path-averaged beam transverse horizontal wind velocity. Two estimators, namely the time delay of the peak (TDP) and slope at zero lag (SZL), both based on the temporal AOA cross-correlation function obtained from a pair of spatially separated LEDs, are utilized for the retrieval of the transverse horizontal wind velocity, v_t. The maximum rms difference between optically retrieved and ultrasonic anemometer measured values of v_t was found to be 0.18 ms^-1 for the TDP estimator and 0.23 ms^-1 for the SZL estimator, over a period of 9 h during which v_t varied between -1.3 ms^-1 and 2.0 ms^-1. An objective treatment of the TDP and SZL wind estimators is presented with respect to their relative accuracy and limitations.