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QLM are developing a novel remote gas imaging sensor for the detection, imaging, and quantification of methane and other greenhouse gas emissions. The sensor combines aspects of Tunable Diode Laser Absorption Spectroscopy (TDLAS) with Differential Absorption Lidar (DIAL) and Time Correlated Single Photon Counting (TCSPC) to enable remote spectroscopy and ranging with low power semiconductor diode lasers. We directly measure the shape of a gas absorption line by continuously sweeping the output wavelength of a diode laser across the line, and simultaneously modulate the laser output to encode the light signal and then use a digital time-domain correlation algorithm between the transmitted and detected light to identify the returned light. By simultaneously tuning the laser wavelength and modulating the amplitude it is possible to determine both the range the laser light has traveled, as with typical Lidar, and the amount of a particular gas that the laser light has passed through, as with typical TDLAS.
Our methane sensors operate around the CH4 absorption line at 1650.9 nm. Tests with calibrated gas cells and controlled gas releases have demonstrated quantification of leak rates as low as 0.01 g/s with accuracy around 25% and detection at distances over 100 m. The accuracy, speed, and practicality of the sensor, combined with an expectation of low-cost in volume, offers the potential that these sensors can be effectively applied for widespread continuous monitoring of industrial methane emissions. We are developing a cloud-based server that automates the collection, analysis and reporting of gas data and provides an autonomous leak monitoring system that can accurately identifying emissions by position, size, and duration.
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