Insights into Elevated Methane Emissions from an Australian Open-Cut Coal Mine Using Two Independent Airborne Techniques

Governments and industries worldwide are seeking methods to accurately estimate their methane inventories, particularly in the open-cut coal mining sector, where quantifying facility-level emissions remains challenging and robust verification methods are not yet widespread. Here, we compare methane emission rates estimated from two aircraft-based measurement platforms with operator-reported emissions from an open-cut coal mine in the Bowen Basin (Queensland, Australia). Coarse-resolution satellite-based data identified the mine as a significant emitter, making it ideal for case studies using airborne in situ and remote sensing platforms that provide high-resolution measurements to isolate mine-scale emissions. Using airborne in situ measurements, we estimated methane emission rates of 14.0 ± 3.3 (±2σ) t h^-1 during May and June 2022. In September 2023, airborne in situ and remote sensing measurements yielded consistent emission rate estimates of 9.6 ± 1.9 (±2σ) t h^-1 and 11.3 ± 5.3 (±2σ) t h^-1, respectively. If sustained, these rates would equate to annual emissions of 1.5-4.2 Mt of CO₂ equivalents (CO₂-e) year^-1, 3-8 times higher than operator-reported annual Scope 1 emissions (0.53-0.54 Mt of CO₂-e year^-1). Beyond highlighting the potential for under-reporting of emissions at this mine, our results indicate that aircraft-based technologies are valuable tools for supporting accurate reporting of facility-scale methane emissions from open-cut coal mines.