Arctic lake methane measured from satellite images
Image credit: Ruth Peterkin | Dreamstime
Researchers have developed a way to use satellite images to measure the amount of methane being released from northern lakes, potentially helping to refine climate change models.
Using synthetic aperture radar, or SAR, a University of Alaska Fairbanks-led team found correlation between “brighter” satellite images of frozen lakes and the amount of methane they produce. By comparing the SAR images with ground-level methane measurements, the team confirmed that the satellite readings were consistent with on-site data.
According to the researchers, SAR data is well-suited to the Arctic. The technology can penetrate dry snow and doesn’t require daylight or cloud-free conditions. SAR is also good at imaging frozen lakes, particularly ones filled with bubbles that often form in ice when methane is present.
“We found that backscatter is brighter when there are more bubbles trapped in the lake ice,” said Melanie Engram, a researcher at UAF’s Water and Environmental Research Center. “Bubbles form an insulated blanket, so ice beneath them grows more slowly, causing a warped surface which reflects the radar signal back to the satellite.”
The technique could have significant implications for climate change predictions; methane is about 30 times more impactful than carbon dioxide as a heat-trapping gas, so precise estimates of its prevalence are particularly important in scientific models.
Previous research had confirmed that vast amounts of methane are released from lakes as the permafrost beneath them thaws. But collecting on-site data from those lakes is often expensive and logistically challenging, so information about methane production is available from only a tiny percentage of Arctic lakes.
“This new technique is a major breakthrough for understanding the Arctic methane budget,” said UAF researcher Katey Walter Anthony. “It helps to resolve a longstanding discrepancy between estimates of Arctic methane emissions from atmospheric measurements and data upscaled from a small number of individual lakes.”
To confirm the SAR data, the researchers compared satellite images with field measurements from 48 lakes in five geographic areas in Alaska. By extrapolating those results, researchers can now estimate the methane production of more than 5,000 Alaska lakes.
“It’s important to know how much methane comes out of these lakes and whether the level is increasing,” Engram said. “We can’t get out to every single lake and do field work, but we can extrapolate field measurements using SAR remote sensing to get these regional estimates.”
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