Understanding Acoustic Emission Testing- Reading 1 Part B-A

The figure 1 shows how the position of the leaking point may be obtained and
the figure 2 shows an example of the cross-correlation function.
The diagram in figure 2 shows that the position of the leak, in relation to the
two sensing devices, is determined by detecting the maximum of the crosscorrelation
function related to the time delay of the signals. (?)
The coherence function shown in figure 3 allows establishing the reliability
rating of the measure carried out. It expresses the dependence of the signals,
detected at the two measurement points A and B, from a common leak noise
source. The Coherence is normally represented between zero and one,
therefore, the nearer the coherence is to one the closer is the link between
the two detected signals. (?)
Charlie Chong/ Fion Zhang
http://www.ndt.net/article/wcndt00/papers/idn183/idn183.htm