Pules Detection Using Cross Correlation
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Accurate timing of acoustic pulses can be carried out by comparing them with a template pulse of similar shape. We have set up a cross-correlation timing procedure for the signals detected by the ORE UVM at 3-Mile Slough.

To the eye, it is often easy to distinguish special features in the graph of a function - a bump, a series of bumps, a signal "turning on" or "turning off." It is not quite as easy to make a computer program do the same thing. Cross correlation is a mathematical way of shifting a template shape along a signal waveform, to determine at what position the two signals line up best. The technique is to calculate the cross-correlation as a function of the shift of the template. It is maximum where the two signals correlate best.

Consider a signal waveform s(t), represented in the computer by an array of length ns, and a template (or replica) waveform r(t), of length nr. The cross-correlation function c(tau) is defined by