At the ecosystem scale, gas emissions are highly variable in both time and space—even at very fine spatial scales (m²). This variability makes it difficult to model gas fluxes accurately and leads to large uncertainties in the estimation of annual budgets. To reduce these uncertainties, a fine-scale spatial analysis (grid of 0.5 m) of gas concentrations and fluxes would improve our understanding of flux distribution, allowing us to :

• Adapt existing measurement protocols to better represent flux variability,

• Identify homogeneous emission areas to produce more accurate flux budgets.

Flux measurements in ecosystems are commonly obtained using three complementary techniques, each with different spatial resolutions :

• Eddy covariance flux measurements (large scale : several hectares), providing high-frequency data (>10 Hz) by correlating gas concentrations with vertical wind speed and direction ;
• Chamber-based techniques, typically using closed chambers over small patches of the ecosystem (<1 m²), to monitor concentration changes over time ;
• Soil gradient methods, offering even finer-scale information, though they are often too labor-intensive to cover sufficient spatial variability.

Understanding the fine-scale drivers of emissions requires spatial analysis of fluxes in relation to key variables such as temperature, vegetation, and soil moisture. While eddy covariance systems cannot provide this spatial resolution and soil gradient methods lack practicality for broad surveys, chamber-based techniques appear most suited for studying spatial flux variability and its drivers.

To date, measurement point selection is often random or based on vegetation cover. However, conducting multiple chamber measurements is time-consuming, and environmental conditions may shift between measurements, affecting flux results. A better-informed analysis of spatial concentration and greenhouse gas (GHG) flux distributions over a short time window would help establish a more efficient and representative sampling protocol that captures the full range of emissions across a site.

The AURORA (Airborne Ultra-light spectRometer fOr tRace gAses flux quantification) sensor—developed within the TERRA FORMA project—is a laser diode spectrometer mounted on a drone, and builds upon earlier instrumentation work by GMSA that led to the AMULSE (Atmospheric Measurements by Ultra-Light SpEctrometer) prototypes. These instruments have already been deployed on stratospheric balloons (0–30 km altitude), tethered balloons, ultralight aircraft, and more recently, on rotary-wing drones as part of the Airborne Ultra-light Spectrometer for Environmental Application project (in collaboration with TOTAL). The goal now is to equip a fixed-wing drone to scan surfaces of up to 3 km² at altitudes between 0 and 150 m, and to measure CO₂ concentrations (range : 100–800 ppm) and CH₄ concentrations (range : 1–10 ppm), with a detection limit of 0.2% at 10 Hz.

These spatial studies may be combined with existing or future eddy covariance or chamber-based measurements to allow for calibration and validation. This approach will also support the development of refined flux measurement protocols for chamber deployments—especially within the footprint of eddy covariance towers. This development responds to a real need within the scientific community for a better understanding of the spatio-temporal behavior of ecosystems, and for improved comparability with existing monitoring methods.

Theme : Soil, Pollution

Presse :

• CNRS-INSU - 19 septembre 2024 - Campagne de mesures de flux de gaz par drone dans le cadre du programme de recherche TERRA FORMA

Updated on 23 juin 2025