The mobile ‘dual-comb’ device adapts Nobel Prize-winning advancements in laser technology to continuously monitor a site for methane leaks. It is looking to replace costly infrared imaging and current spectrometer technology that is currently used to identify methane leaks.
Methane leak detection prevents a harmful greenhouse gas from entering the atmosphere and avoids wasting a valuable commodity; in a 2012 study, the National Resource Defence Council estimated that $2 billion (€1.6 billion) in revenue was lost to the natural gas industry due to leaks. This new technology allows for continuous measurement and increased sensitivity. The researchers are aiming to bring the cost of the device down to $300 (€243).
The leak detector uses ‘the world’s first’ field-ready dual-frequency comb laser spectrometer combined with corner cube retroreflectors. The team behind the development comes from the National Institute of Standards and Technology (NIST), the University of Colorado Boulder (CU Boulder) and the National Oceanic and Atmospheric Administration (NOAA).
Current methods use infrared cameras and spectrometers either attached to an aircraft or used manually to assess leakage in an area. Such techniques are laborious, time consuming and expensive, resulting in infrequent testing.
The comb laser spectrometer is a laser that generates a series of short (some millionth billionths of a second), equally spaced pulses of light. The technology has enabled advances in areas like chemical analysis and fibre-optic communications. John L. Hall of NIST shared the 2005 Nobel Prize in Physics for advancements in the area.
The laser pulses, like teeth on a comb, measure the spectral signature of any material they pass through. The ‘dual-comb’ detector uses two laser combs to increase precision: “When paired, the combs can act like hundreds of thousands of laser spectrometers working in unison, and yield a device that is 10 to 100 times better than a traditional spectrometer and very sensitive to leaks, even at a great distance,” said Ian Coddington, a NIST physicist and co-author of the paper.
A computer model is used to take local weather conditions and non-process related methane into account: “The monitoring can be done continuously over time so that every leak in a field is accurately detected and quantified,” said Kuldeep Prasad, a NIST mechanical engineer who helped design the computer model. “Furthermore, if you set up mobile spectrometers at adjoining fields, you can dramatically expand the total coverage area to several square kilometres.”
He added that, where line-of-site leak detection is impossible, the spectrometer can be placed above the site to assess gas leaks as the methane rises.
The study is called ‘Regional trace-gas source attribution using a field-deployed dual frequency comb spectrometer’ and was published in the journal Optica.