Evaluation of UAV-based methods for quantifying methane point source emissions

Abstract. Uncrewed aerial vehicles (UAVs) are increasingly becoming essential monitoring tools across a rapidly growing set of applications, due to their operational versatility,  relatively low operating cost, and provision of data at a range of spatial scales. However, UAV-based measurement methodologies and associated instruments for atmospheric research are still in their early stages and require extensive efforts to exploit their full potential. In Arctic regions, geological CH4 seeps can  release CH4 at rates significantly higher than typical biogenic sources and those associated with permafrost degradation processes; hence, accurate quantification of their emission rates is crucial for the overall CH4 budget of the Arctic. The application of conventional greenhouse gas monitoring platforms – flux chambers and eddy-covariance towers – may become impractical as eddy-covariance towers are stationary point measuring devices that require long observation times with reliable footprint modeling to constrain emissions while flux chambers have a small footprints and therefore require multiple measurements and have a high potential of introducing disturbances. UAVs can overcome these limitations as they can capture the spatial extent of the gas plume released from a point source with minimal disturbance to the source. In July 2025, we deployed two UAV platforms with different sensing instruments to sample a known geological CH4 seep located at the Mackenzie River Delta, Canada. We flew vertical "curtain" patterns with open-path and closed-path CH4 instruments to sample gas concentrations in flux planes at different downwind distances from the gas seep. We first evaluated the performance of the UAV-mounted instrumentation, comparing the open- and closed-path greenhouse gas analyzers. We then compared two widely used quantification techniques – mass-balance and Gaussian plume inversion – finding that mass-balance approaches yielded the most robust quantification with smaller uncertainties. We estimate that the seep emission rate falls in the range of 7.1 to 16.2 kg CH4 h-1, with an average estimated rate of 11.4 ± 6.8 kg CH4 h-1. The emissions from this single point are equivalent to the biogenic flux from approximately 2.2 km2 of the surrounding permafrost landscape, underscoring the need to assess the potentially significant contribution of geological seeps to regional and pan-Arctic carbon budgets.