Cavity Ring-Down Methane Sensor for Small Unmanned Aerial Systems

Abstract

We present the development, integration, and testing of an open-path cavity ring-down spectroscopy (CRDS) methane sensor for deployment on small unmanned aerial systems (sUAS). The open-path configuration used here (without pump or flow-cell) enables a low mass (4 kg) and low power (12 W) instrument that can be readily integrated to sUAS, defined here as having all-up mass of <25 kg. The instrument uses a compact telecom style laser at 1651 nm (near-infrared) and a linear 2-mirror high-finesse cavity. We show test results of flying the sensor on a DJI Matrice 600 hexacopter sUAS. The high sensitivity of the CRDS method allows sensitive methane detection with a precision of ~10–30 ppb demonstrated for actual flight conditions. A controlled release setup, where known mass flows are delivered, was used to simulate point-source methane emissions. Examples of methane plume detection from flight tests suggest that isolated plumes from sources with a mass flow as low as ~0.005 g/s can be detected. The sUAS sensor should have utility for emissions monitoring and quantification from natural gas infrastructure. To the best of our knowledge, it is also the first CRDS sensor directly deployed onboard an sUAS.

Testing the near-field Gaussian plume inversion flux quantification technique using unmanned aerial vehicle sampling

“…They can fly near the source and can be directed automatically using waypoints to enable even and unbiased spatial sampling (Greatwood et al, 2017;Feitz et al, 2018). There are three principal approaches for measuring methane mole fraction from a UAV in situ: on-board air samples can be collected for subsequent analysis (Chang et al, 2016;Greatwood et al, 2017;Andersen et al, 2018), air can be pumped through a long tube to a sensor on the ground for analysis (Brosy et al, 2017;Wolf et al, 2017;Shah et al, 2019) or air can be analysed live using a sensor mounted on board the UAV (Berman et al, 2012;Khan et al, 2012;Nathan et al, 2015;Golston et al, 2017;Martinez et al, 2020). Yet, a key limitation to accurate source identification and flux quantification is the precision and accuracy of methane mole fraction measurements (Hodgkinson and Tatam, 2013).…”

“…Some studies have used UAV remote-sensing measurements to derive emission fluxes (Golston et al, 2018;Yang et al, 2018). However, to our knowledge, only Nathan et al (2015) have derived fugitive methane emission fluxes using UAV in situ measurements. In that study, a UAV with an on-board in situ low-precision sensor (±0.1 ppm at 1 Hz) flew in orbits around a gas compressor station, using mass balance box modelling, with geospatial kriging for interpolation, to derive the emission flux.…”

Development of Drone-Mounted Multiple Sensing System with Advanced Mobility for In Situ Atmospheric Measurement: A Case Study Focusing on PM2.5 Local Distribution

“…For this study, we used a large industrial drone (Matrice 600 Pro; SZ DJI Technology Co., Ltd., Shenzhen, China) as a platform to measure atmospheric phenomena using the mounted MSS. Because of its advanced functionality, versatility, and scalability, this drone model has been applied in numerous studies and research projects [ 82 , 83 , 84 , 85 , 86 , 87 , 88 , 89 , 90 , 91 , 92 ] in various application fields. According to the official specifications provided by the manufacturer, the total weight and the maximum payload are, respectively, 10 kg and 6.0 kg.…”

Modeling landfill CH4 emissions

“…Such transient events can lead to significant fugitive CH 4 emissions, some of which are addressed under current U.S. landfill regulations which require a quarterly gridded "walkover" survey using a portable CH 4 analyzer, followed by timely remediation. Given rapidly evolving sensor (Martinez et al, 2020) and drone technology (Daug_ ela et al, 2020;Kim et al, 2021), it is likely that the surface detection methods can be significantly expanded, especially from localized areas that may not be currently included (i.e., steep slopes). Finally, of particular importance at U.S. landfills is the relatively common practice of removing an existing intermediate cover prior to vertical expansions for new cell development-this exposes fully methanogenic older waste resulting in very high CH 4 emissions per unit area from a small footprint (Cambaliza et al, 2017; Figure S4).…”