Abstract
Abstract. A compact and lightweight mid-infrared laser absorption spectrometer has been developed as a mobile sensing platform for high-precision atmospheric methane measurements aboard small unmanned aerial vehicles (UAVs). The instrument leverages two recent innovations: a novel segmented circular multipass cell (SC-MPC) design and a power-efficient, low-noise, intermittent continuous-wave (icw) laser driving approach. A system-on-chip hardware control and data acquisition system enables energy-efficient and fully autonomous operation. The integrated spectrometer weighs 2.1 kg (including battery) and consumes 18 W of electrical power, making it ideally suited for airborne monitoring applications. Under stable laboratory conditions, the device achieves a precision (1σ) of 1.1 ppb within 1 s and 0.1 ppb CH4 at 100 s averaging time. Detailed investigations were performed to identify and quantify the effects of various environmental factors, such as sudden changes in pressure, temperature, and mechanical vibrations, which commonly influence UAV-mounted sensors. The instrument was also deployed in two feasibility field studies: an artificial methane release experiment and a study on vertical profiles in the planetary boundary layer. In both cases, the spectrometer demonstrated its airborne capability of capturing subtle and/or sudden changes in atmospheric CH4 mole fractions and providing real-time data at 1 s time resolution.
Highlights
Global emissions of methane are continuing to increase, making CH4 a relevant component for managing realistic pathways to mitigate climate change, especially with nearterm benefits (Shindell et al, 2012)
This was motivated by two practical factors: (i) distributed feedback quantum cascade lasers (DFB-QCL) with high optical power can readily be used, and (ii) the P branch of the ν4 band is at the edge of the atmospheric window – i.e., interfering absorption due to water vapor is considerably weaker
Equipped with a highpower thermoelectric cooler (TEC)-assembly mounted on a water-cooled heat sink (Lytron Inc., USA), the chamber allows for rapid temperature modulation
Summary
Global emissions of methane are continuing to increase, making CH4 a relevant component for managing realistic pathways to mitigate climate change, especially with nearterm benefits (Shindell et al, 2012). They can provide valuable information about the spatial and temporal variability in emissions regardless of terrain complexity or pollution source characteristics This significantly extends the scale and the level of detail of measurements compared to those provided by traditional stationary monitoring networks. The potential of this approach is well reflected by the increasing number of reported commercial as well as research-grade sensors and related applications (e.g., Berman et al, 2012; Villa et al, 2016, and references therein). The majority of these solutions are triggered by oil and gas industry fugitive emission monitoring
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