Abstract
This paper reports for the first time the fully optical remote monitoring of low-level CH4 gas with a wide area coverage of 10 km in diameter realized by utilizing ultralowloss silica optical fibre link and a compact absorption cell in conjunction with highly radiant InGaAsP and InGaAs light emitting diodes (LEDs) in the near infrared region. For this novel application, the near-infrared absorption spectra of CH4 molecules were measured and studied involving the ν2+2ν3 combination band around 1.33 μm and the 2ν3 overtone band around 1.66 μm. This fibre-optic system was demonstrated to be feasible and sufficiently sensitive and safe as being a practical CH4 gas remote sensor whose detection sensitivity is normally required to be 25% of the lower explosion limit (LEL) of CH4 gas in air. This result verifies a large potential for applying extensively to various strategic points within the environment, such as industrial and mining complexes as well as urban and residential areas, with considerably increased reability, safety and marketability over the presently available techniques.
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