Active Stand-off Detection of Gas Leaks Using a Short Range Hard-target Backscatter Differential Optical Absorption System Based on a Quantum Cascade Laser Transmitter

Adrian Diaz,Fred Moshary,Benjamin Thomas,Paulo Castillo,Barry Gross,B Gross,F Moshary,M Arend

doi:10.1051/epjconf/201611905013

Abstract

Fugitive gas emissions from agricultural or industrial plants and gas pipelines are an important environmental concern as they can contribute to the global increase of greenhouse gas concentration. Moreover, they are also a security and safety concern because of possible risk of fire/explosion or toxicity. This study presents gas concentration measurements using a quantum cascade laser open path system (QCLOPS). The system retrieves the pathaveraged concentration of N 2 O and CH 4 by collecting the backscattered light from a scattering target. The gas concentration measurements have a high temporal resolution (68 ms) and are achieved at sufficient range (up to 40 m, ~ 130 feet) with a detection limit of 2.6 ppm CH 4 and 0.4 ppm for N 2 O. Given these characteristics, this system is promising for mobile/multidirectional remote detection and evaluation of gas leaks. The instrument is monostatic with a tunable QCL emitting at ~ 7.7 μm wavelength range. The backscattered radiation is collected by a Newtonian telescope and focused on an infrared light detector. Puffs of N 2 O and CH 4 are released along the optical path to simulate a gas leak. The measured absorption spectrum is obtained using the thermal intra-pulse frequency chirped DFB QCL and is analyzed to obtain path averaged gas concentrations.

Highlights

In order to reduce greenhouse gas concentrations, there is a need for tools able to detect fugitive gas emissions from agricultural, industrial plants, or natural gas pipeline infrastructure
We present a potential system for fast gas concentration measurements based on a distributed feedback quantum cascade laser (DFB - QCL), its central wavelength of emission when used in a long pulsed (200+ nanoseconds) mode is rapidly chirped during the course of the pulse resulting in a well defined frequency sweep allowing this type of laser to be use for intra-pulse spectroscopy [6]
In order to perform mobile or multidirectional remote detection of fugitive gas emission, we demonstrate in this contribution a backscatter

Summary

Introduction

In order to reduce greenhouse gas concentrations, there is a need for tools able to detect fugitive gas emissions from agricultural, industrial plants, or natural gas pipeline infrastructure. Optical methods to measure fugitive emission flux has been developed in order to detect greenhouse (or hazardous) gases [2,3,4,5], these methods are appropriate for fugitive emissions as they cover larger area than point sensors. In this contribution, we present a potential system for fast gas concentration measurements based on a distributed feedback quantum cascade laser (DFB - QCL), its central wavelength of emission when used in a long pulsed (200+ nanoseconds) mode is rapidly chirped during the course of the pulse resulting in a well defined frequency sweep allowing this type of laser to be use for intra-pulse spectroscopy [6]. Laboratory measurements have been performed on methane (CH4) and nitrous oxide (N2O), respectively the second and third most potent anthropogenic greenhouse gases [1] over a distance of 40 meters (~ 130 ft) and with a high temporal resolution (68 ms)

Methods

Results

Conclusion