Investigation of passive acoustic anemometer by use of wind noise correlation

This paper examines feasibility of an acoustic anemometer by evaluating estimates of wind directions and wind velocities towards microphone array. These estimates are calculated based on a number of delay times among pair-microphones. To obtain the delay times, a low-frequency correlation of coherence function between wind noises for pair-microphones is practically utilized. This paper firstly discusses about the validity of the estimation method for wind direction and wind velocity by means of simulated wind noises to obtain some high-precision results. Secondly, the estimation accuracies of the wind directions and the wind velocities are evaluated for wind noises recorded in a practical environment. The winds are generated by a tower fan and recorded by three microphones that are closely located at each vertex of a triangle. The results for the recorded wind noises show that estimation errors are heavily dependent on the recording direction in contrast to the results for the simulated wind noises. Since these fluctuations of the errors are commonly observed in several recorded wind noises, a correction for unknown estimates is approximately calculated by employing some known estimates and their errors. As a result, the average relative error of the wind velocity was 5.4 % and the average absolute error of the wind direction was 6.64 deg. This correction method indicated the efficacy of estimating the wind directions and the wind velocities.