correlator works by detecting sound from the leak when it arrives at
sensor points positioned at each side of the suspected leak position.
The sound arrives at the closer of the two sensors first, then there
is a “time delay” (Td) before the sound arrives at the farther sensor.
This time delay, combined with the knowledge of the distance (D) of
pipeline between the sensors and the velocity (V) of the sound in the
pipe , enables the correlator to calculate the leak position (L)