On the effects of reflections on time delay estimation for leak detection in buried plastic water pipes

This paper is concerned with the way in which wave reflections in a fluid-filled pipe affect the cross-correlation function of two leak noise signals used to detect and locate leaks in buried water pipes. Propagating waves generated by leak noise reverberate in a pipe network system, as they encounter features such as changes in section, and resistance such as valves, and pipe junctions. A theoretical model of a straight pipe with discontinuities, which cause reflections, is developed and incorporated into a model of the cross-correlation function. The reasons why the reflections and the low-pass filtering properties of the pipe can be largely removed by the generalised cross-correlation (GCC) phase transform (PHAT) are determined. Using the analytical model, theoretical predictions of the basic cross-correlation function (BCC) and the GCC PHAT are compared with experimental data from a specially constructed test site in Canada.