Development of an open-path, laser dispersion spectroscopy (LDS) analyser for the measurement of large area methane emissions

Graham Leggett, MIRICO (GB)

Laser Dispersion Spectroscopy (LDS), is a new gas sensing technique that applies a novel approach to tunable diode laser spectroscopy. Common techniques depend on measuring detected intensity to derive concentration. This significantly impacts measurements in “dirty” environments where detected intensity of the transmitted light is bound to fluctuate. MIRICO’s LDS-based instrument derives concentration using the phase of light. This makes it highly immune to intensity fluctuations received at the photodetector. The instrument enables precise, real time measurements of trace gas molecules in demanding environments. Furthermore, compared to absorption techniques, the analyser can measure gas concentrations within a very wide dynamic range (typically about five to six orders of magnitude), meaning for example from parts per billion all the way to sub percent concentrations without the requirement for dilution.

In a long open-path, multi-direction configuration, coupled with a retroreflector array, and anemometer, the LDS analyser is capable of measuring concentrations of methane and ethane associated with large area sources, and locating and quantifying point source emissions within said area. Here we describe the principle of LDS, and the development of the prototype instrument. In addition, we report the results of a pilot study where the capabilities of the LDS instrument set-up described above was tested using a controlled release of methane from a point source within a large target area.


Pen Profile

Graham graduated with a Ph.D. from University of London in 1999.  His thesis presented the development of new purification strategies for the purification of gases, and solvents, used in the semiconductor fabrication process.  He continued working for his sponsor, Air Products, for several years, developing and commercializing new purification technologies.

This was followed by seven years at National Physical Laboratory as a senior research scientist in the Gas Metrology Group working on the development of trace gas standards.
After time with the environmental consultancy, AEA Technology, he then spent periods with US analytical instrument manufacturers, Tiger Optics, and Picarro, both of which develop cavity ring-down instruments for industrial and scientific applications.

As of July 2016, Graham has been instrumental in a new venture, MIRICO Ltd.  Key on his agenda is to bring the company’s Laser Dispersion Spectroscopy to market, working to identify new markets, and applications, and steer product development.


+31 (0)15 2 690 448