UAV-based CH4 flux estimation intercomparison using controlled releases within the IM4CA project

Methane (CH₄) is a key driver of near-term climate warming, and rapid mitigation requires robust, independent, and spatially resolved quantification of emissions, including their temporal variability and intermittency. Within the IM⁴CA (Investigating Methane for Climate Action) project, Unmanned Aerial Vehicles (UAVs) are being developed as flexible platforms to support emission monitoring and verification at the scale of individual sources. However, differences in instrumentation, flight strategies, and emission quantification methodologies can lead to substantial variability in derived flux estimates across teams and campaigns.

To address this challenge, a dedicated UAV intercomparison campaign was conducted in December 2025 at the Unmanned System Research Laboratory (USRL), near Orounda, Cyprus. Over five days, four research teams: Utrecht University (UU), The Cyprus Institute (CyI), AGH University Krakow (AGH), and the National Institute for Aerospace Research Elie Carafoli (INCAS), performed coordinated UAV measurement flights at a common site, targeting a controlled CH₄ release with known emission rates.

The teams operated with differing levels of platform independence: UU and CyI flew their instruments on their own UAVs, AGH deployed their sensor both on their own platform and on a CyI UAV, while INCAS operated their CH₄ sensor exclusively on a CyI platform. Meteorological data were collected using ground-based stations operated by CyI and AGH around the runway, as well as onboard measurements from the UU UAV. Controlled methane releases were designed to allow each team to sample all release rates under comparable environmental conditions. The emission rates, ranging from 0 to 25 kg h-1, were known by the release operator but disclosed to the teams only after the campaign, ensuring an unbiased intercomparison.

In this contribution, we first describe and compare the experimental setups of the participating teams, including sensor technologies, UAV platforms, and flight strategies. We then present and intercompare the CH₄ flux estimates derived from each system for identical release periods, focusing on accuracy relative to the known CH₄ flux, their internal consistency, and sensitivity to environmental conditions, such as wind speed and atmospheric stability. Differences arising from flight patterns, data processing choices, background determination and flux estimation methodologies are examined. The results will provide critical insight into the strengths and limitations of the UAV-based methane quantification approaches used in the context of the IM⁴CA project, and support robust results in future project-wide campaigns.