Sound velocity measurement in acoustic leak noise correlation systems

In this paper, the acoustic leak noise correlation method is applied for the measurement of the sound velocity of the propagated acoustic signal in water filled metallic pipes. Artificially introduced leaks are used as out-of-bracket excitation signal sources. The standard time domain correlation method is adopted for the computation of the required difference time of arrival between noise leakage signals propagating in the pipeline network, which are collected by the use of accelerometers mounted on the surface of the pipe. A new method is proposed for the improvement of the accuracy of the measured sound velocity, introducing a technique of estimation fusion, based upon results obtained from multiple measurements. A simple to use formula is derived for the enhancement of the accuracy of the estimation, introducing a weighted mean of the estimations over various realizations, with the weighting coefficients depending upon the the quality of each estimator and on the geometric characteristics of each experiment. The effectiveness of the proposed method is demonstrated using experimental data for (a) the measurement of the sound velocity and (b) the localization of artificially introduced in-bracket leaks using the measured sound velocity.