Development of an airborne Eddy covariance system dedicated to greenhouse gases (CO2/CH4) and energy fluxes measurements of heterogeneous landscapes onboard fixed-wing UAV

Climate change poses significant threats to ecosystems and human activities, necessitating urgent efforts to reduce greenhouse gas emissions. This requires new tools able to monitor and quantify emissions at the meso-scale, applicable to large industrial facilities, agricultural sites, landfills or natural areas such as forests or peatlands. To address this challenge, our project aims at developing a lightweight (< 4 kg) eddy covariance (EC) system embarked on a fixed-wing vertical take-off and landing (VTOL) uncrewed aircraft system, enabling precise measurements of greenhouse gases (CO₂, CH₄) and energy fluxes between the surface and the atmosphere over large and heterogeneous areas. 

The system combines a five-hole turbulence probe (ADP) to measure three-dimensional wind and air temperature, along with a custom-fabricated diode laser spectrometer for CO₂, CH₄ and H₂O concentrations. The gas analyzer is lightweight (2.1 kg), highly accurate (< 0.5 %), capable of rapid measurements (100 Hz) and optimized for high-speed mobile platforms. 

A preliminary mobile EC system (comprising the ADP, a reference sonic anemometer and the custom gas analyzer) was mounted on a vehicular platform to evaluate the integrated sensor suite under real atmospheric conditions. Comparative analyses of instantaneous relative velocity components and turbulence spectra show close agreement between the two wind sensors, confirming the ADP’s suitability for integration into our VTOL-based EC system. Furthermore, the water vapor and CO₂ concentration spectra indicate that the concentration sensor is well-suited for measuring atmospheric gases within a mobile EC setup. A continuous wavelet transform approach was applied to compute surface fluxes on agricultural fields near the road trip. Combined with a footprint analysis to study landscape heterogeneity, this lays the groundwork for a transition to a drone-based EC system.  

A flight maneuver was conducted with the ADP-equipped VTOL under unstable atmospheric conditions to validate wind and air temperature measurements. Spectral analysis indicates that the airborne platform can capture actual atmospheric turbulence. Sensible heat flux was computed for this test flight, demonstrating our drone-based EC system’s potential to generate surface fluxes and emissions maps over heterogeneous landscapes. 

As part of our future work, flight trials will be carried out to measure greenhouse gases (CO₂ and CH₄) and energy fluxes. These measurements will be compared against tower-based EC fluxes to evaluate the performance of the UAV-based system.