A methane controlled release system for small and intermediate emission quantification with associated drone airspace

Methane (CH4) is a key short-lived climate forcer, making accurate emission quantification essential for climate mitigation strategies. Methods to estimate CH4 emissions from sources such as landfills, wetlands, agriculture, and the oil and gas sector using atmospheric concentration measurements are available and relatively well established, yet their practical implementation remains challenging and they lack standardization. Emission estimates are sensitive to numerous factors, including measurement techniques (e.g. differential absorption lidar, optical gas imaging, diode laser absorption spectroscopy), measurement platforms (e.g. satellite, aircraft, drone, vehicle, ground-based station, handheld system), sites size and complexity, meteorological conditions, signal processing and quantifications approach (e.g. gaussian plume or mass-balance). 

To test and validate methods aiming at small and medium leak-like emissions under realistic conditions, the Cyprus Institute (CyI) developed an open-air controlled-release site capable of generating CH4 emissions from 0 to 25 kg h-1, spanning a wide range of real-world emission scenarios. It is located at the Unmanned Systems Research Laboratory (USRL) airfield of CyI, on the Orounda plateau approximately 40 km from Nicosia, Cyprus. The facility includes two runways (200 m × 12 m and 90 m × 6 m) and is surrounded by flat access roads, providing a versatile environment for drone-based and vehicle-mounted measurements. The controlled-release system consists of two units enabling the distribution and precise flow control of high-purity CH4 (99.5%), connected to a dedicated 180 m-long hose (1-inch inner diameter). The gas outlet (open-ended release) is located at a height of 3.2 m above ground level. Multi-level wind measurements are provided by three wind sensors installed at heights of 13 m, 8 m, and 2.5 m. 

We present this controlled release system, its operations, and associated uncertainties in flow rates. It has been first used during the IM4CA (Investigating Methane for Climate Action) campaign, intercomparing UAV-based and car-based in-situ methane quantification techniques from 8 to 11 December 2025. As USRL is a National Facility (in the framework of ACTRIS), it can be accessed on a Transnational Access (TNA) basis by a large number of users and can provide access to a large and diverse fleet of fixed and rotary-wing UAS.