The ultrasonic noise probe or gas detector detects points of entry of high-pressure gas into an open borehole by listening for an ultrasonic signature.

PRINCIPLE OF MEASUREMENT:

Sound energy caused by gas entering a borehole is focussed by a conical acoustic mirror within the probe onto a microphone. The microphone is tuned to measure the acoustic energy in a frequency band centred at 40kHz., characteristic of entry of high-pressure gas through a narrow orifice.