A drone-based method for simultaneous flux measurements of multiple greenhouse gases at hectare-scale with in-flight calibration and tracer gas release

<jats:p>Abstract. Convenient in situ methods are key for detecting, quantifying, and mitigating gas emissions. Uncrewed aerial vehicles (UAVs), comprising drones equipped with lightweight integrated instruments, offer a promising platform for mapping greenhouse gas (GHG) emissions. However, flux area attribution can be challenging, and the low-weight gas analyzers or sensors required for drones may exhibit drift over time that degrades detection limits and increases measurement uncertainty. We have developed a UAS (uncrewed aerial system) based approach with all instrumentation onboard, mapping gases, here focusing on simultaneous measurements of the GHGs methane (CH4), carbon dioxide (CO2), nitrous oxide (N2O), and ethane (C2H6). The key innovations are the combination of onboard multi-gas measurements, in-flight drift correction using onboard reference air, and integration of controlled tracer gas (C2H6) release to constrain the area attribution of detected fluxes. We explore four different flight patterns (box, two-wall, long wall, and 2D-mapping), each suited to different measurement scenarios, and demonstrate their application in diverse environments, including a rewetted peatland, the littoral zone of a lake, manure wells, and a barn housing dairy cows. Our results show the importance of in-flight drift correction or drift control, and that this can reduce baseline-related uncertainty of UAS-based mass balance approaches, which can be key for improving detection limits and estimation of GHG fluxes in a wide range of environments and settings. Furthermore, combining tracer gas emissions with drone flights aids in separation of sources in the area of interest, verification that targeted emissions are intercepted by the sampling walls, and determination of the upper integration height needed to capture source-related transport.</jats:p>