Imaging of methane gas using a scanning, open-path laser system

We have developed an imaging system for the detection and of methane gas leaks. The system is based on a distributed feedback laser diode emitting at 1.65μm, the beam from which is directed at objects. The backscattered light is collected by a Fresnel lens and the concentration is deduced from the reduction in collected intensity as measured a second derivative wavelength modulation technique. The incident laser the collected beam are both scanned over an area to form an image of the gas . To ease the task of locating the source of the emission, we combine the low-resolution image of the gas emission with a high-resolution colour of the scene. Our results show that the system can image a gas cloud of 1mm effective thickness at a range of several metres, sufficient to detect a gas of 1 litre min−1 in light to moderate winds.