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.
ABSTRACT
A multi-channel Raman lidar has been developed, allowing for the first time simultaneous and high-resolution profiling of hydrogen gas and water vapor. The lidar measures vibrational Raman scattering in the UV (355 nm) domain. It works in a high-bandwidth photon counting regime using fast SiPM detectors and takes into account the spectral overlap between hydrogen and water vapor Raman spectra. Measurement of concentration profiles of H2 and H2O are demonstrated along a 5-meter-long open gas cell with 1-meter resolution at 85 meters. The instrument precision is investigated by numerical simulation to anticipate the potential performance at longer range. This lidar could find applications in the French project Cigéo for monitoring radioactive waste disposal cells.
