A Vehicle-Based Remote Methane Detector Using Absorption Molecular Spectroscopy

The design and manufacturing of a fast, high sensitivity and portable remote sensor for methane detection is reported. This system acts based on Tunable diode laser absorption spectroscopy (TDLAS) using the second harmonic spectroscopy (SHS), as a detection method. The emitter is a tunable distributed feedback laser (DFBL) centered at wavelength 1653 nm. The optical receiver subsystem collects the weak light backscattered from the ground (soil, sands, etc.) and introduces it into a Photodetector (PD). The electrical signal after PD is amplified and processed by a home-made lock-in amplifier (LIA) and then is sent to Lab.View software for extracting the methane concentration information on a PC. This system was able to detect minimum detectable concentration down to 80 ppm-m from 20 m away at 300 ms integration time. By using the more precise LIA (Stanford Instrum.) and unamplified PD, measurement of concentrations up to 20 ppm-m at a distance of 20 meters was possible. This minimum detectable concentration allows the application of the device in the regular pipeline inspection.