Abstract
This study examines the feasibility of applying ground-based hyperspectral imaging to monitor methane (CH4) concentrations at landfills. The hyperspectral imaging system implemented in this study is an imaging Fourier transform spectrometer (IFTS) that operates in the long-wavelength infrared (LWIR) spectrum, between 750 and 1350 cm-1. The instrument produces a three-dimensional absolute intensity data cube, where the first two dimensions define the image plane and the third dimension corresponds to the wavenumber spectrum. The intensity spectrum of each pixel can be inverted using a spectroscopic model to infer air temperature, background temperature, and CH4 and H2O column densities. Additionally, the gas velocity near the surface can be visualized by tracking features in interference-corrected interferogram images. The findings show that this technique can image CH4 column densities from both diffuse and point sources within landfills, provided there is an adequate thermal contrast between the background surface and the air column between the background surface and the camera aperture. The capability to obtain images of CH4 column densities and velocimetry from the IFTS opens the potential for estimating CH4 emissions rates from landfills.Implications: The ability to image methane is crucial for monitoring and studying landfill methane emissions, given their high spatial variability. Hyperspectral imaging of methane from landfills is often conducted via airborne or satellite-based imaging techniques, which are often associated with low spatial resolution (~30 m) and rely on reflective sunlight. Our manuscript presents methane field test results from active and closed landfills using ground-based hyperspectral imaging operating in the long-wavelength infrared spectrum, which enables higher spatial resolution (~7 cm) and demonstrates the capability to image methane using thermal radiation from the background surface. The manuscript also discusses the uncertainty associated with the operating conditions of the technology.