Evaluating metre-scale methane plume simulations with MicroHH against AVIRIS-4 remote sensing observations

Abstract. High-resolution imaging spectrometers resolve anthropogenic plumes at metre to sub-metre scales, creating opportunities for emission quantification but requiring models that reproduce turbulent plume morphology at comparable resolution. We evaluate the large-eddy simulation model MicroHH against Airborne Visible/Infrared Imaging Spectrometer (AVIRIS-4) observations from 2024 controlled releases in France. Using site-specific wind, surface, and source parameters, we simulated the four releases with the longest plumes at 1 m horizontal resolution. Synthetic CH₄ column enhancements were evaluated using plume structure, turbulence spectra, Gaussian cross-section statistics, along-plume flux variability, and plume power spectral density. For one release with a pronounced double plume, we integrated the three-dimensional model field along the slant illumination and viewing paths to investigate parallax effects. MicroHH reproduced the expected inertial-subrange behaviour of turbulent kinetic energy spectra and observed plume width, intermittency, and spatial power spectra for most releases. However, modelled vertical columns were more Gaussian than the observations and did not reproduce the double plumes. The exploratory slant-path calculation generated a comparable double structure, indicating that observational geometry can explain part of this discrepancy. Other differences likely reflect rapid near-source dilution at finite grid resolution, the absence of online plume-rise and buoyancy treatments, and omitted obstacle effects on near-surface flow. Overall, MicroHH can generate realistic high-resolution synthetic plume imagery for retrieval evaluation and machine-learning applications when inputs are well constrained and observational geometry is considered. This first systematic multi-metric comparison of LES plume morphology with metre-scale imaging-spectrometer observations provides a validation framework for other high-resolution dispersion models.