Quantifying methane emissions from mud volcanoes using in-situ fixed-wing drone measurements

Azerbaijan hosts one of the largest global concentrations of mud volcanoes, which are natural geological formations that erupt mud, water, and gases, with methane (CH₄) being the dominant component. Here, we present results from the recent METHANE-To-Go Azerbaijan field campaign, which aimed to quantify CH₄ emissions from mud volcanoes using in-situ fixed-wing drone measurements.

The campaign was carried out mainly in two field phases in May and October 2025, supplemented by additional flights throughout the year, resulting in a total of 36 flight hours. Measurements were performed using a fixed-wing MAS DIHA 350 VTOL UAV equipped with a lightweight, high precision CH₄ analyzer, along with wind measurements derived from pitot tube data. A dedicated measurement strategy was developed and optimized specifically for mud volcanoes in the Azerbaijani environment. The approach follows a mass balance framework based on Gauss’s divergence theorem, whereby the drone flies concentric circles around the emission source at multiple altitudes. Fluxes of CH₄ are derived from upwind and downwind measurements, enabling the quantification of the total emission enclosed by the cylindrical flight pattern. To validate the applied methodology, five controlled release experiments were conducted, during which CH₄ from bottles was released at a known rate. Additionally, two dedicated flights were conducted to calibrate and evaluate the in-situ wind measurements using the onboard pitot tube. In total, 38 measurement flights were conducted at five continuously emitting mud volcanoes, allowing for quantitative emission estimates for these sites. In addition to continuously emitting sources, the method was applied to an explosive eruption of the Otmanbozdagh mud volcano on 11 October 2025, which was surveyed shortly after the event.
In parallel to the flight measurements, ground based air samples were collected and analyzed for gas composition and CH₄ carbon stable isotopes, supporting source attribution and the discrimination of mud volcano emissions from potential anthropogenic sources.

The dataset provides the first high resolution in-situ CH₄ observations shortly after a mud volcano eruption, as well as quantitative emissions from active mud volcanoes using mass balance approach, indicating source dependent emission rates on the order of several tens to approximately one hundred kilograms per hour. These results contribute to a more robust assessment of the role of geological CH₄ sources in the global climate system and demonstrate the potential of fixed-wing drone platforms for quantitative measurements of greenhouse gas fluxes.