抄録
We have developed a vehicle mounted methane detector by means of 1.65-micron LD (Laser Diode) spectroscopy combined with a mobile GIS (Geographic Information System). The detector is used for high-speed survey of gas leakage from underground pipelines.
The detection limit of the detector is about 70 ppb in optical path length of 1 meter with time constant of 1 second. This high sensitivity is achieved by second-harmonic detection of modulation frequency of the LD the center wavelength of which is stabilized on the center of an absorption line of methane.
The position of the vehicle is determined with accuracy of 1-3 meters by a vehicle positioning machine which is connected to a DGPS (Differential GPS, GPS: Global Positioning System) receiver and a fiber-optic gyroscope. Survey tracks and detection points are displayed and recorded on the mobile GIS which consists of information of pipeline network, streets, buildings and so on.
