A high-precision laser spectrometer for methane monitoring aboard UAVs
"Deploying unmanned aerial vehicles (UAV) for methane sensing can provide valuable information on the spatial and temporal variability of methane sources at a level of detail that is not attainable with measurements from traditional stationary monitoring networks.
We report on the development of a lightweight, open-path absorption spectrometer for the measurement of atmospheric methane concentration. The spectrometer is based on a single-mode quantum cascade laser (DFB-QCL). The absorption signal is enhanced by using a novel circular, segmented multi-pass cell with an optical path length of 10 m that has a compact footprint, and shows low optical noise and high stability against mechanical distortion. The instrument weighs 1.6 kg (excluding battery) and has an average power consumption of 15 W. Low heat dissipation is achieved by intermittent continuous wave laser driving and a system-on-chip FPGA data acquisition module. The spectrometer is equipped with additional sensors for pressure, temperature and relative humidity, as well as a GPS receiver and an optional module for real-time data transmission. Therefore, it is possible to use the device aboard any drone, regardless of its specific communication protocol.
Our methane sensor reaches a precision of a few ppb at 1 s time resolution and significantly below 1 ppb after 10 - 1000 s integration. It has been regularly flown on a commercial drone (DJI Matrice 600). The open-path design allows very fast sampling, and absorption spectra are measured at > 10 kHz. This gives a wide flexibility in terms of the required precision and time resolution. Ongoing field experiments illustrate the potential of this unique instrument for the identification, characterization and quantification of natural and anthropogenic methane sources."
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Bela Tuzson (EMPA)
Bela Tuzson is a research scientist at Empa, the Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Air Pollution and Environmental Technology. The current activity focuses on instrumental developments based on laser spectroscopy and their application in environmental, industrial, and medical research
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