Uncertainties in quantifying coal mine shaft CH4 emissions from in-situ and remote sensing instruments using high-resolution plume modelling

Methane emissions from coalmine shafts contribute significantly to anthropogenic greenhouse gas emissions to the atmosphere. Strategies to quantify and monitor these emissions include remote sensing (using aircraft and satellite imagers) and in-situ measurements (aircraft and UAV measurement campaigns). Each technique offers distinct advantages and limitations. However, quantifying the efficacy and the uncertainties of measurement techniques remains challenging. Here, we use a Large Eddy Simulations (LES) model called Fire Dynamics Simulations (FDS), which can model methane plumes at high-resolutions (<1m). To validate the LES model, we used plumes measured by a HySpex instrument placed approximately 1 km from the Pniowek V coal mine in Poland, next to a Doppler LiDAR instrument able to measure the wind profile.

FDS simulates high-fidelity CH₄ plumes compared to the observations, including the angle at the release, the concentration values, and the height of the plume at various distances from the source. Based on our validation, we simulated high-resolution tracks for in-situ instruments (UAV), which measure the near-field of the CH₄ plume, and also plume images at a slightly lower resolution (5-30 m) for satellite and aircraft imagers, which measure long-distance plumes.  Methane plumes correspond to various velocity values of releases and mine’s air concentrations, under various environmental conditions (mean wind speed, air temperature, relative humidity) to construct an ensemble of simulated experiments. We conclude this study by comparing the effectiveness of each individual method in terms of emissions uncertainties, aiming at monitoring CH₄ emissions from the ventilation shafts of deep coal mines.