Mapping methane plumes in AVIRIS-NG India campaign data and potential for global point source emissions monitoring using imaging spectroscopy

Quantifying methane point source emissions requires imaging of plumes at high spatial resolution, a task that airborne imaging spectrometer (a.k.a. hyperspectral) data are well-suited for. We present the results of an effort to detect and measure methane plumes imaged during the NASA/ISRO Next Generation Airborne Visible-InfraRed Imaging Spectrometer (AVIRIS-NG) campaigns in India. Over 300 flightlines of data at an approximate spatial resolution of 8m were acquired from 57 sites during the Phase 1 India campaign. Sites included a diversity of land uses, including urban, agriculture, mining, and forest, and a similarly diverse Phase 2 campaign is currently underway. Improved matched filter algorithms were used to detect methane plumes, estimate concentration, and suppress background and spurious signals. Concentrations estimated using a linearized matched filter were compared to concentrations retrieved through differential optical absorption spectroscopy (DOAS). All campaign data were processed, and methane plumes emitted from landfills, wastewater treatment, and petroleum production were mapped and quantified. The strongest plume was emitted from the Pirana landfill in Ahmedabad and was mapped extending nearly 5 km downwind from the source. To evaluate the potential for mapping point source emissions using a satellite imaging spectrometer, 30 m spatial resolution data were simulated from the AVIRIS-NG images. Most points sources examined were still detectable at 5 nm spectral resolution. Ability to detect small methane plumes was reduced at 10 nm spectral resolution, but many point sources could still be detected. Data used in this study will be provided as a new benchmark dataset for furthering algorithm development, assessing scalability of point source monitoring for planned and proposed imaging spectrometers, and understanding the characteristics of Indian point source emissions.