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

Abstract

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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> . The maximum rms difference between optically retrieved and ultrasonic anemometer measured values of v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> was found to be 0.18 ms <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> for the TDP estimator and 0.23 ms <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> for the SZL estimator, over a period of 9 h during which v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> varied between -1.3 ms <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and 2.0 ms <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . An objective treatment of the TDP and SZL wind estimators is presented with respect to their relative accuracy and limitations.