Methane leak detection and sizing over long distances using dual frequency comb laser spectroscopy and a bootstrap inversion technique

Abstract

Abstract. Advances in natural gas extraction technology have led to increased activity in the production and transport sectors in the United States, and, as a consequence, an increased need for reliable monitoring of methane leaks to the atmosphere. We present a statistical methodology in combination with an observing system for the detection and attribution of fugitive emissions of methane from distributed potential source location landscapes such as natural gas production sites.We measure long (>500 m), integrated open path concentrations of atmospheric methane using a dual frequency comb 15 spectrometer and combine measurements with an atmospheric transport model to infer leak locations and strengths using a novel statistical method, the non-zero minimum bootstrap (NZMB). The new statistical method allows us to determine whether the empirical distribution of possible source strengths for a given location excludes zero. Using this information, we identify leaking source locations (i.e., natural gas wells) through rejection of the null hypothesis that the source is not leaking. The method is tested with a series of synthetic data inversions with varying measurement density and varying levels 20 of model-data mismatch. It is also tested with field observations of 1) a non-leaking source location and 2) a source location where a controlled emission of 2.1 E-5 kg s -1 of methane gas is released over a period of several hours. This series of synthetic data tests and outdoor field observations using a controlled methane release demonstrate the viability of the approach for the detection and sizing of very small (<2 g m -1 ) leaks of methane across large distances (4+ km 2 in synthetic tests). The field tests demonstrate the ability to attribute small atmospheric enhancements of 18 ppb to the emitting source 25 location against a background of combined atmospheric (e.g., background methane variability) and measurement uncertainty of 6 ppb (1-sigma), when measurements are averaged over 2 minutes. The results of the synthetic and field data testing show that the new observing system and statistical approach greatly decreases the incidence of false alarms (that is, wrongly identifying a well site to be leaking) compared with the same tests that don't use the NZMB approach, and therefore offers increased leak detection and sizing capabilities. 30Atmos. Meas. Tech. Discuss., https://doi

20 years of developments in optical frequency comb technology and applications

“…Generation of difference frequencies within the optical spectrum also allows for high-fidelity frequency transfer to the mid-infrared, terahertz, and microwave domains. OFCs quickly found application to a multitude of diverse optical, atomic, molecular, and solid-state systems, including X-ray and attosecond pulse generation 4 , coherent control in field-dependent processes 5,6 , molecular fingerprinting 7 , trace gas sensing in the oil and gas industry 8 , tests of fundamental physics with atomic clocks 9 , calibration of atomic spectrographs 10 , precision time/frequency transfer over fiber and free-space 11 , arbitrary waveform measurements for optical communication 12 , and precision ranging 13 . To support this broad application space, OFCs have seen rapid changes in laser development to enable coverage at different spectral regions, varying frequency resolutions, and to enable the development of systems that offer lower size, weight and power (SWAP) [14][15][16][17] .…”

Laser Absorption

“…Additionally, it is somewhat challenging to achieve high temporal resolution and wide wavelength coverage simultaneously. Frequency combs have recently been developed to an extent where they are relatively compact in size and have been deployed in power plant facilities as well as in field applications to detect species concentrations and other parameters of interest [27][28][29]. More details on the application of frequency-comb laser spectroscopy are discussed in Sec.…”

“…Recently, high-resolution comb lasers have been used to detect methane leaks (Fig. 8.22) in a relatively large area by utilizing laser absorption spectroscopy technique [28]. The open-path sensors were able to detect leaks that are smaller than the volume of exhaled breath.…”

20 years of developments in optical frequency comb technology and applications

“…Generation of difference frequencies within the optical spectrum also allows for high-fidelity frequency transfer to the mid-infrared, terahertz and microwave domains. Optical frequency combs quickly found application to a multitude of diverse optical, atomic, molecular and solid-state systems, including X-ray and attosecond pulse generation 4 , coherent control in field dependent processes 5,6 , molecular fingerprinting 7 , trace gas sensing in the oil and gas industry 8 , tests of fundamental physics with atomic clocks 9 , calibration of atomic spectrographs 10 , precision time/frequency transfer over fiber and free-space 11 , arbitrary waveform measurements for optical communication 12 , and precision ranging 13 . To support this broad application space, OFCs have seen rapid changes in laser development to enable coverage at different spectral regions, varying frequency resolutions, and to enable the development of systems that offer lower size, weight and power (SWAP) [14][15][16][17] .…”