A team of scientists just completed a series of flights over California to develop new methods of detecting and measuring carbon dioxide and methane in the atmosphere. These gases, linked to climate change, arise from a variety of human activities, such as landfills and the burning of fossil fuels. There are also natural sources – such as the La Brea Tar Pits in Los Angeles – a prominent emitter of methane.
The Carbon Dioxide (CO2) and MEthane eXperiment, known as COMEX, used multiple aircraft to measure the atmosphere and compare it to estimates from passive airborne spectroscopy – the "colors" the gases leave in sunlight. COMEX has collected data for key methane sources in the San Joaquin Valley and the Greater LA Area, including oil production and refining, animal husbandry, natural geology, and landfills with supporting in situ airborne (i.e., flights within the actual plumes of gas) and surface data for validation of higher-altitude airborne information. Methane is a potent greenhouse gas that the Intergovernmental Panel on Climate Change (IPCC) expects will have a greater overall impact in the near term (i.e., over the few decades) on the atmosphere than carbon dioxide.
"Our understanding of methane emissions from many important sources remains poor," said Ira Leifer, NASA COMEX principal investigator at Bubbleology Research International in Solvang, California. "For example, a recent review of many field studies over the last decade concluded that industrial fossil fuel emissions – the primary methane source – had been underestimated by a factor of approximately two."
To this end, NASA and ESA equipped aircraft provided by the Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS) at the Naval Postgraduate School in Monterey, California, with instruments, including the University of Bremen, Germany-developed Methane Airborne Mapper (MAMAP) sensor. MAMAP is a non-imaging spectrometer that makes plume transits at high spectral resolution and with high sensitivity to carbon dioxide and methane. CIRPAS also flew a greenhouse gas detector adapted for flight by NASA's Ames Research Center in Moffett Field, California.
MAMAP was complemented by the Airborne Visual InfraRed Imaging Spectrometer Next Generation (AVIRIS-NG) developed by NASA's Jet Propulsion Laboratory in Pasadena, California, which images, or "maps" methane at a higher spatial resolution but lower spectral resolution and sensitivity than MAMAP. AVIRIS-NG flew onboard a separate airplane. In addition, another AVIRIS sensor called AVIRIS Classic flew high above in the stratosphere aboard NASA's high-altitude Earth Research-2 airplane, based at NASA's Armstrong Flight Research Center's facility in Palmdale, California. Two additional airplanes performed in situ observations of the larger area atmosphere, and mapped methane using infrared remote sensing of COMEX study areas.
The COMEX remote sensing instruments detect many hundreds of "colors" spanning the visible and infrared spectrum – far more than what the human eye can see. These instruments make atmospheric measurements from the shading of colors in sunlight due to greenhouse gases, humidity and particles in the atmosphere.
"Methane emissions occur globally with most sources occurring outside United States' borders," said Leifer. "There is a critical need for a global measurement capability to address and understand the impact of this global issue."
COMEX also informs potential future satellite missions in both the U.S. and Europe. NASA is studying a possible mission known as the Hyperspectral Infrared Imager or HyspIRI. ESA considers the CarbonSat mission a candidate for its Earth Explorer 8, to be launched in 2022. COMEX provides test data sets, design guidance and improved emission algorithms for these activities.
"COMEX has demonstrated the complementary nature of U.S. and European approaches to measuring atmospheric methane" said Woody Turner NASA Headquarters program scientist. "For example, the AVIRIS instruments’ higher spatial-resolution surface albedo (surface color) can improve MAMAP methane maps, while MAMAP's better spectral resolution measurements can improve AVIRIS surface observations of ecosystem type, health and diversity."
"COMEX has acquired a worldwide unique data set to determine methane emissions from combined remote sensing and in-situ observations," said Heinrich Bovensmann, ESA COMEX PI from University of Bremen. "COMEX has demonstrated the power of remote sensing to study methane emissions with these instruments. One day, these assets will play a critical role in providing high quality information to decision makers, regulators and the public to guide policy development."
NASA and ESA jointly fund COMEX, which is a partnership of scientists at NASA's Ames Research Center in Moffett Field, Bubbleology Research International, the University of Bremen, Germany, the Naval Postgraduate School, Aerospace Corporation in El Segundo, California, and ESA. ESA funds the University of Bremen's contribution to COMEX within the CarbonSat mission preparatory program and is also providing some funding for the CIRPAS aircraft. Aerospace participation was supported under Aerospace’s Independent Research and Development program.