Active methane gas imaging and leakage quantification based on standoff TDLAS and pan-tilt units

Abstract

Methane (CH₄) is the main component of natural gas. Natural gas leakage can cause economic losses and safety hazards, making its accurate detection and quantification a critical issue in the natural gas industry. We developed a non-cooperative target-based, low-cost active standoff gas sensor for imaging and quantifying CH₄ leaks. The sensor is developed based on tunable diode laser absorption spectroscopy (TDLAS) to measure the path-integrated concentration of atmospheric CH₄. The wavelength modulation spectroscopy with first harmonic normalized second harmonic detection (WMS-2f/1 f) method is applied to reduce the measurement errors caused by the variation of the echo laser intensity. The key to active imaging is a pan-tilt unit integrating the standoff CH₄ sensor, a laser rangefinder, and a visible camera. With 2D scanning, CH₄ concentration data, ranging data, and pan-tilt angular data are fused to generate a pseudo-color map of CH₄ concentration. Further, the CH₄ leakage rate is estimated by a mass balance algorithm based on the wind speed data collected by an anemometer. The imaging quality and quantification accuracy were evaluated by targeting calibrated CH₄ gas bags and controlled CH₄ gas release at different concentrations. The experiments show that the developed sensor can detect CH₄ leaks down to 0.1 g/s at 30 m range and quantify leaks with accuracy better than 10 % at 10 m range, which demonstrates its potential for application in the natural gas industry.