A portable remote methane detector using an InGaAsP DFB laser
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A portable remote methane detector based on infrared-absorption spectroscopy using an InGaAsP distributed-feedback laser is described. This equipment transmits a laser beam and detects a fraction of the backscatter reflected from the target. From this, the detector thereby measures the integrated methane concentration between the detector and the target. The equipment operator can easily detect methane clouds at a distance by hand-scanning the laser beam. To achieve a high sensitivity of detection, wavelength-modulation spectroscopy is applied to the infrared-absorption measurement for methane. The wavelength of the light source is modulated at a frequency of 10 kHz, and the center wavelength is stabilized at the center of the 2ν3 band R(3) line of methane (1.65372 μm). When used with typical targets at distances up to 10 m, the detector has a detection limit of less than 5 ppm-m. To the best of the author’s knowledge, the detector is the only hand-held product capable of remote methane detection. Recently, this novel equipment was commercially introduced into the Japanese market as a product named the Portable Remote Methane Detector (PRMD). Some PRMD units were in research use for detecting methane emissions from garbage landfills, although the PRMD was mainly developed for remote detection of leaks from natural gas pipelines. The author expects that the PRMD could become the standard equipment for field measurements of methane emissions from land.
KeywordsMethane Remote sensing Tunable diode laser absorption spectroscopy (TDLAS) Wavelength modulation spectroscopy (WMS)
The author expresses thanks to his research group members in Tokyo Gas Co. Ltd., Anritsu Corporation, and Tokyo Gas Engineering Co. Ltd. for their cooperation during the development of the PRMD. The author also wish to thank Dr. Tanikawa, associate professor of the Hokkaido University, Dr. Yamada, Senior researcher of the National Institute for Environmental Studies, and Dr. Ishigaki, researcher of the National Institute for Environmental Studies, for their valuable advise.
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