Remote methane sensor using raman amplified open path TDLS

Reported here is a long-range optical methane sensor designed with the purpose of enabling more efficient leak monitoring of natural gas pipelines, oil rigs and gas containers including ships. Combining sensitive Wavelength Modulation Spectroscopy (WMS) and a high power Raman amplifier system, the sensor launches a high power 1650.95nm signal at an inspection site at a distance of around 100m and analyses the backscatter via a large Fresnel lens to detect methane concentrations of 100ppm in a 1m gas cloud up to 100%. The work comprises the design and testing of a low-noise high-power fibre Raman amplifier system as a remote methane sensing source. Seeded by a single-mode 1650.95nm laser (DFB), upon which the WMS modulation is applied, the Raman amplifier produces a highpower, narrow-band methane sensing signal. Key to the system’s competitive advantage is its low cost, small size, low weight, high reliability and superior performance when compared to bulk long-range airborne systems. This results from designing a fibre based system that is constructed entirely from standard communications fibre and components. Lab trials at 11m have been conducted and show by extrapolation that a 1m cloud of methane at a concentration of 100ppm can be detected with a signal to noise ratio of 3:1 at a range of >100m