This paper has reported the design and installation of a highly multiplexed (45 point) methane gas detection system using single mode fibre optics linked to remote miniature open path absorption cells interrogated by a single DFB laser diode configured for frequency modulation spectroscopy. To our knowledge this is the first such system to be site tested. The system operates over a wide area with total link lengths from source to detector extending up to about 6 km and has proved to be rugged and stable through the operating conditions on an active methane gas producing landfill site. Initial results on a small scale trial system give optimism for future reliability and the system behaviour will continue to be closely observed. It also seems very probable that the data obtained from continuous positioning will give new insights into site dynamics. Within its present configuration the system could be readily extended to address 64 points though we believe that, for this application, a 128 point system is totally feasible and a 256 point system may be achievable.
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