Abstract
Abstract. At local scales, emissions of methane and carbon dioxide are highly uncertain. Localized sources of both trace gases can create strong local gradients in its columnar abundance, which can be discerned using absorption spectroscopy at high spatial resolution. In a previous study, more than 250 methane plumes were observed in the San Juan Basin near Four Corners during April 2015 using the next-generation Airborne Visible/Infrared Imaging Spectrometer (AVIRIS-NG) and a linearized matched filter. For the first time, we apply the iterative maximum a posteriori differential optical absorption spectroscopy (IMAP-DOAS) method to AVIRIS-NG data and generate gas concentration maps for methane, carbon dioxide, and water vapor plumes. This demonstrates a comprehensive greenhouse gas monitoring capability that targets methane and carbon dioxide, the two dominant anthropogenic climate-forcing agents. Water vapor results indicate the ability of these retrievals to distinguish between methane and water vapor despite spectral interference in the shortwave infrared. We focus on selected cases from anthropogenic and natural sources, including emissions from mine ventilation shafts, a gas processing plant, tank, pipeline leak, and natural seep. In addition, carbon dioxide emissions were mapped from the flue-gas stacks of two coal-fired power plants and a water vapor plume was observed from the combined sources of cooling towers and cooling ponds. Observed plumes were consistent with known and suspected emission sources verified by the true color AVIRIS-NG scenes and higher-resolution Google Earth imagery. Real-time detection and geolocation of methane plumes by AVIRIS-NG provided unambiguous identification of individual emission source locations and communication to a ground team for rapid follow-up. This permitted verification of a number of methane emission sources using a thermal camera, including a tank and buried natural gas pipeline.
Highlights
It is important to better understand the processes controlling changes in atmospheric methane (CH4) and carbon dioxide (CO2), the two dominant anthropogenic climate-forcing agents
IMAP-DOAS retrievals for only a few examples will be presented here, reflecting CH4, CO2, and H2O plumes from a variety of emission sources
CO2 emissions were observed from the flue stacks of two coal-fired power plants and an H2O plume was mapped for the cooling towers for one power plant
Summary
It is important to better understand the processes controlling changes in atmospheric methane (CH4) and carbon dioxide (CO2), the two dominant anthropogenic climate-forcing agents. In situ airborne measurements offer the potential for increased coverage and have been used for US regional CH4 flux estimates using mass balance approaches for the Uintah Basin in northeastern Utah (Karion et al, 2013), the Marcellus formation in southwestern Pennsylvania (Caulton et al, 2014), and the Barnett Shale formation in Texas (Smith et al, 2015; Lavoie et al, 2015) These measurements reflect gas concentrations at the flight altitude and these studies are designed to estimate aggregate emissions for large regions rather than identifying individual emissions sources. In situ airborne measurements using a chemically instrumented Mooney aircraft have been used to estimate fluxes from known sources like the Aliso Canyon leak (Conley et al, 2016) and for a number of sources identified by imaging spectrometers in the Four Corners region (Frankenberg et al, 2016) This method samples the atmosphere directly at the flight path altitude and can measure multiple gas species. Both instruments are better suited for either investigating known emission sources or identifying larger regional emissions as opposed to individual sources
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