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The view from space: plotting methane leaks

World Coal,

Researchers from NASA and the University of Michigan have used satellite mapping data to plot occurrences of methane leaks from coalbed methane (CBM) operations.

In a recent study, the research showed that an unexpectedly high amount of methane is escaping from the Four Corners region in the US Southwest

Four Corners sits on North America’s most productive CBM basin.

"There's so much coalbed methane in the Four Corners area, it doesn't need to be that crazy of a leak rate to produce the emissions that we see. A lot of the infrastructure is likely contributing," said Eric Kort, assistant professor of atmospheric, oceanic and space sciences at the U-M College of Engineering.

Kort added that drilling techniques, including hydraulic fracturing or ‘fracking’ were not the cause of the leaks.

"We see this large signal and it's persistent since 2003," Kort said. "That's a pre-fracking timeframe in this region. While fracking has become a focal point in conversations about methane emissions, it certainly appears from this and other studies that in the US, fossil fuel extraction activities across the board likely emit higher than inventory estimates."

Study contributor, Christian Frankenberg, at Jet Propulsion Laboratory, said that the high methane spot didn’t equate with high emissions of greenhouse gasses. "The Four Corners methane source is in a relatively isolated area with little other methane emissions, hence causing a well distinguishable hot-spot in methane abundances,” he said.

CBM operations are keen to prevent methane leaks where possible, since methane has 30 times the short-term heat-trapping effects of carbon dioxide. However, until now pinpointing leaks has been a difficult task.

Current tools at tracking methane often prove ineffective, however, this satellite-led data demonstrates a new approach to finding leaks.

Methane gets into the atmosphere from both natural and human-made sources. Wetlands and landfills release it, as do certain bacteria. Agriculture is a big contributor. So are gas and oil drilling and distribution. Inventories such as those the EPA compiles make estimates based on measurements from a sampling of these sources. In previous work, air measurements from planes and a sparse network of monitoring towers have revealed that the inventory-based numbers are coming in low – roughly 50% low. But towers and planes can't see everywhere to figure out exactly where all the methane is coming from. With limited observations there can be blind spots, the researchers say.

A satellite instrument – the European Space Agency's SCIAMACHY – provides regional methane measurements over the entire US. The researchers then ran the data through a mathematical model to account for mountains and valleys, which can trap methane. In this way, the team identified the anomaly at Four Corners. Then they zoomed in on that region and ran another mathematical model to control for wind, to make sure that didn't negate the original signal, which it did not.

"We didn't know this was a region we should look at. We found it from space," Kort said. "We've demonstrated that satellite measurements can help identify, locate and quantify anomalous methane emissions in regions that are unexpected."

This study used satellite data from 2003 – 2009. In later years, they were able to validate the satellite measurements with a year of ground-based data.

SCIAMACHY is no longer operating, so there are not equivalent satellites to provide this information for other parts of the world. For the Four Corners region, Kort will be taking readings from an airplane next year, to get even closer to identifying the leaks.

Edited from various sources by Sam Dodson

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