Airborne imaging spectrometer measurements of methane releases under turbulent conditions

Methane plume detection and quantification from airborne and spaceborne platforms offers a promising approach for monitoring localized greenhouse gas emissions. Its performance must be demonstrated under realistic but controlled conditions. An airborne demonstrator of a compact shortwave infrared imaging spectrometer developed for the AIRMO Earth observation mission was therefore evaluated during a single-blinded methane release experiment at the TotalEnergies Anomaly Detection Initiatives (TADI) facility in Lacq, France. Measurements were conducted over three days in June 2025 at an altitude of ~2050 m above ground level, with controlled release rates ranging from 12.2 to 104.4 kgCH4/h. Methane plumes, i.e. spatially coherent column averaged enhancements (ΔXCH4) were detected and corresponding mass fluxes quantified for emission rates ≥54 kgCH4/h, with occasional detections at 15.2 kgCH4/h under favourable conditions. The corresponding probability of detection was ~50% overall and ~75% for releases ≥54 kgCH4/h. Retrieved source locations were typically within ±30 m of the true release point, and plume lengths ranged from ~40 to ~270 m. Radiometric uncertainty and wind speed uncertainty both dominated retrieved fluxes. Testing high temporal resolution wind data from an in-situ meteorological station in comparison to ERA5 wind data led to more accurate (closer to truth) flux retrieval, provided the optimal averaging time window was known. The latter was found to be longer than typical plume residence times. These results provide valuable guidance for the design of future airborne and spaceborne methane monitoring missions, including the AIRMO concept integrating imaging spectroscopy with micro-lidar aerosol profiling.