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Mapping and quantifying methane emissions from local sources using airborne imaging spectrometers

  • Author(s): Thorpe, Andrew
  • Advisor(s): Roberts, Dar A
  • et al.
Abstract

Most of the existing techniques for detecting, quantifying, and attributing point source emissions of methane (CH4) have relied on ground-based measurements. These methods are limited either by their spatial resolution or temporal coverage, which makes identifying the location of individual sources challenging. By combining large image footprints and fine spatial resolution, airborne imaging spectrometers offer the potential to permit direct attribution of emissions to individual point sources.

This dissertation explores the potential of using imaging spectrometers like the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) and the next generation sensor (AVIRIS-NG) for high resolution mapping of emissions and quantification of methane concentrations present within scenes. To do so, non-quantitative filtering methods and quantitative methane retrievals were adapted for use with AVIRIS and AVIRIS-NG scenes over both marine and terrestrial environments. These techniques were applied to scenes acquired at natural marine methane seeps (Coal Oil Point, COP) and for natural and anthropogenic sources in the Los Angeles Basin. At these locations, distinct plumes consistent with local wind direction were observed. As part of this study, I developed methods of reducing noise and false positives in results.

As part of a controlled release experiment, AVIRIS-NG was flown at multiple flight altitudes and methane flux rates to determine its sensitivity for methane detection. From these results, detection rates were calculated for multiple flux rates and indicate a detection threshold around 3.4 cubic meters per hour (0.02 kt/year). Given this threshold, AVIRIS-NG has the potential to detect a number of fugitive methane source categories for natural gas fields. Ongoing analysis of AVIRIS-NG scenes over oil and gas fields indicates multiple methane plumes, further emphasizing the utility of imaging spectrometers for direct attribution of methane emissions.

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