Methane emissions from fossil fuel production are estimated as one of the major sources of the greenhouse gas CH4, estimated responsible for ~30% the radiative transfer impact of CO2, yet, virtually no peer-reviewed studies have field-evaluated these emissions, which EPA estimates are the largest non-anthropogenic US CH4 source. The current state of knowledge is in part because of the need for imaging spectrometric remote sensing, recently first demonstrated with AVIRIS (Airborne Visual Infrared Imaging Spectrometer) for a marine geologic source and sunglint. The approach is to use vicariously collected AVIRIS hyperspectral data during transit between Ellington AFB and the oil spill, during the current mission (Leifer is Airborne Mission Coordinating Scientist for the NASA spill response) of Gulf of Mexico platform flaring (>4300 active platforms). Typical uncombusted flaring CH4 is 5x106 m3 dy-1. These data will ground reference GOSAT data (Leifer/Roberts are on the GOSAT science team). Platform sources will be far easier to evaluate than the geologic source, and AVIRIS could collect order ~1000 platform-source observations over the current mission, but not critical ground reference measurements. Results also will aid future satellite platform development, like HyspIRI.
This RAPID study uses SEBASS (hyperspectral thermal IR, allowing high cloud/nighttime observations) to map CH4 plumes from a Twin Otter with far higher spatial resolution than AVIRIS (during transit), which also allows in situ air sampling at a range of altitudes and down wind distances. Plume modeling allows radiative transfer-derived column-CH4 validation by in situ data. SEBASS is configured for tactical (near real time plume visualization) CH4 plume identification, allowing sample collection guidance. Hundreds of air samples will also be collected in evacuated cans and vials per flight-day from the Twin Otter as well as from surface vessels. This RAPID is thus part of a coordinated effort in response to the Gulf oil leak. The ultimate result will be an estimate of methane emissions from the Gulf oil leak.
Abstract: Due to its radiative importance and decade lifetime, estimated responsible for ~30% the radiative transfer impact of CO2 [Shindell et al., 2009], understanding methane budgets requires a large-scale view, typically satellite. The focused goal of the Rapid grant was to use the opportunities provided by NASA flights in response to the BP oil spill to collect AVIRIS (Airborne Visual InfraRed Imaging Spectrometer) data for derivation of methane emissions from offshore platforms, and to collect ground reference data. Remote sensing data were collected for this study by the AVIRIS instrument onboard the NASA ER2 airplane and the Aerospace Corporation’s, SEBASS Thermal Infrared Imaging Spectrometer. Supporting data were collected from analysis of vessel and airplane air samples collected during the DWH event. Additional supporting methane data were collected during two transcontinental expeditions across the US in 2010 and 2013, and during a research cruise in the Gulf of Mexico in 2013. Finally, the context of these data was provided by comparison with SCIAMACHY and GOSAT satellite data to better understand the overall role of Fossil Fuel Industrial (FFI) methane emissions to overall methane budgets on a Gulf of Mexico Basin basis. Additional surface data were collected for FFI and also natural geologic sources in California for comparison with Gulf of Mexico FFI sources. Thermal hyperspectral imaging confirmed surface boat findings that minimal methane was reaching the atmosphere from the Deepwater Horizon blowout, and successfully identified CO2 plumes from offshore activities related to DWH vessel operations. A cluster trained matched filter approach was demonstrated as successful at identifying plumes from venting in AVIRIS Gulf overflight data. The episodic nature of seepage also was identified (Bradley 2013). Surface vessel measurements during DWH showed negligible methane, in agreement with other studies, but also an exceptionally very heavy load of higher hydrocarbons. A simple plume transport model was applied to the source and composition data and typical winds to estimate exposure for coastal communities. Using a gasoline health model, it was found that levels were high enough to be of concern to at risk portions of coastal populations, such as infants. Satellite-scale surface methane data were collected in 2010 and 2013, for comparison with satellite data and showed that methane anomalies were correlated with FFI activities, and moreover, that in some areas and seasons, these data could be used to conclude that inventories were significantly under-estimating emissions. It also was found that FFI emissions exhibit seasonality. (Leifer et al 2013; Farrell et al 2013) It was shown that transcontinental surface datasets are extremely useful for validating satellite data sets. Surface data allows direct investigation of sources, which can be challenging from airborne platforms, often requiring modeling to discriminate between multiple sources (Leifer et al 2013). References Bradley, E. S. (2013), Characterizing methane emissions at local scales with a 20 year total hydrocarbon time Sseries, imaging spectrometry, and web facilitated analysis, 234 pp, University of California, Santa Barbara. Farrell, P., I. Leifer, and D. Culling (2013), Transcontinental methane measurements: Part 1. A mobile surface platform for source investigations, Atmospheric Environment, 74, 422-431. Leifer, I., D. Culling, O. Schneising, P. Farrell, M. Buchwitz, H. Bovensmann, and J. P. Burrows (2013), Transcontinental methane measurements: Part 2. Mobile surface investigation of fossil fuel industrial fugitive emissions Atmospheric Environment, 74, 432-441. Shindell, D. T., G. Faluvegi, D. M. Koch, G. A. Schmidt, N. Unger, and S. E. Bauer (2009), Improved attribution of climate forcing to emissions, Science, 326(5953), 716-718.
