UAV-based methodologies for quantifying methane emissions from point sources

Uncrewed aerial vehicles (UAVs) are increasingly becoming complementary monitoring tools in various scientific fields, particularly in atmospheric and climate science, as they are versatile, relatively cheap, and can provide data at various spatial scales. However, UAV-based methodologies are still in their early stages and require extensive effort to fully exploit the potential of UAVs. Accurate quantification of emission rates from point or localized sources, such as geologic seeps or oil and gas production sites, is important for understanding emission processes and mitigating climate change. Conventional greenhouse gas monitoring platforms (i.e., flux chambers and eddy-covariance towers) have a significant sampling gap as they struggle to provide the spatial extent needed to accurately estimate emission rates from point or localized sources. UAV platforms carrying greenhouse gas analyzers for CO2 and CH4, along with an anemometer to measure 2D wind speed, air temperature, humidity, and pressure, allow capturing the spatial extent of a plume originating from a point source, and therefore accurately quantify its source strength.

The UAV platform employed for this study was used to sample a geological methane seep located in the Mackenzie Delta, Canada. Geological methane seeps can act as super emitters, releasing methane at rates significantly higher than typical biogenic sources; hence, accurate quantification of their emission rates is crucial to estimate the overall CH4 budget of the area. In July 2024, different flight strategies were tested to monitor point sources, including several curtain flights and a grid flight conducted at varying downwind distances from the seep. Using these flight data, the emission rate of the methane seep was quantified using two different methods: a mass-balance approach and a Gaussian plume inversion technique. The CH4 plume released from the seep showed concentrations about ten times higher than the atmospheric CH4 background levels, underscoring the significant potential impact of the geological seeps on the overall Arctic carbon budget.