Abstract
We report on the performances of a coherent DIAL/Doppler fiber lidar called VEGA, allowing for simultaneous measurements of methane and wind atmospheric profiles. It features a 10µJ, 200 ns, 20 kHz fiber pulsed laser emitter at 1645 nm, and it has been designed to monitor industrial methane leaks and fugitive emissions in the environment. The system performance has been assessed for range-resolved (RR) and integrated-path (IP) methane measurements in natural background conditions (i.e. ambient methane level). For RR measurements, the measured Allan deviation at τ=10 s is in the range of 3-20 ppm, depending of the aerosol load, at a distance of 150 m, with 30 m range resolution, and a beam focused around 150-200 m. For IP measurements, using a natural target at 2.2 km of distance, the Allan deviation at τ=10 s is in the range of 100-200 ppb. In both cases, deviation curves decrease as τ-1/2, up to 1000 seconds for the longest averaging time. Finally, the lidar ability to monitor an industrial methane leak is demonstrated during a field test.
Highlights
With a high warming global potential, methane is known as one of the most important greenhouse gas to monitor
Wind measurements have shown a good agreement with a reference instrument, while methane IP measurements have been consistent with the expected value
The measurement precision for methane has been assessed in details, and random error models have shown to be in good agreement with statistically observed errors
Summary
With a high warming global potential, methane is known as one of the most important greenhouse gas to monitor. Several CH4 lidars, either range-resolved or path-integrated, have been reported before, employing direct detection systems and solid-state pulsed lasers like Optical Parametric Oscillators/Amplifiers (OPO/OPA) or Er:YAG cavities [2,3,4,5,6,7,8]. These systems generally show very good performances but exhibit a high number of free-space optics, for which alignment and long-term stability can be an issue, especially in harsh or vibrating environment conditions
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