Satellite supergroup spots methane super-emitters

ESA’s Copernicus program provides satellite data that enable scientists around the world to monitor climate change and support mitigation efforts. One of the great challenges is the mitigation of methane, the second most important greenhouse gas contributing to climate change. Combining observations from three Copernicus satellites – Sentinel-5P, Sentinel-3, and Sentinel-2 -now enables researchers to detect and zoom in on methane hot spots in a tiered approach and identify the responsible super-emitters.

Methane is responsible for a quarter of human-induced global warming and provides a short-term lever on climate change because it remains in the atmosphere for a much shorter time than CO2. So, knowing where the largest methane emissions occur is key to evidence-based decision making and successful mitigation. Therefore, when the Sentinel 5 Precursor satellite was launched in 2017, expectations and hopes were high. The only instrument onboard Sentinel-5P, the Dutch TROPOspheric Monitoring Instrument (Tropomi), was going to scan the entire globe for a range of trace gases  including methane, every day and at city scale (7 x 5.5 km2) resolution.

The results have been staggering. The Dutch space research institute SRON (co-principal investigator of Tropomi) has for instance used TROPOMI’s global coverage to find methane emission hot spots around the world. These Tropomi hot spots have subsequently been targeted with high-resolution (25 meters) observations from the Canadian GHGSat satellites, which are able to pinpoint the exact sources. In this way, the researchers found a great number of methane super-emitters, varying from fossil fuel facilities to individual landfills.

However, GHGSat observations cannot cover the entire world and only part of the observations are publicly available. The gaps have recently partly been filled with land-imaging satellites such as Sentinel-2, that have been found capable of detecting the largest methane leaks under favorable observing conditions such as over deserts. Sentinel-2’s high-resolution observations (20 m) provide global coverage every 5 days and were designed to provide operational data products for environmental risk management, land cover classification, land change detection. Sentinel-2 is especially powerful to detect methane leaks in a tiered approach, where Tropomi Sentinel 5P is used to tip-and-cue high spatial resolution satellites.

Missing link
The tiered approach has now become even more compelling using Sentinel-3, as researchers at SRON Netherlands Institute For Space Research and JPL show in this week’s published paper. Zooming in on an area as large as 7 x 5,5 km2 to pinpoint a fossil fuel facility at Sentinel-2’s resolution can be challenging. Moreover, as Sentinel-2 observes  locations only every 5 days, chances are that short-term methane emissions like gas blowouts escape identification. That is where Sentinel-3 comes in. With daily global coverage and the ability to pinpoint the largest methane point sources to within 500×500 m2 (under favorable observing conditions), Sentinel-3 is the missing link between Tropomi and Sentinel-2. Sentinel-3’s daily global coverage is also particularly important for large leaks that only last a few hours and could easily go unnoticed between Sentinel-2 overpasses.

Tiered approach
“The secret is the tiered approach,” SRON-researcher Sudhanshu Pandey (now at JPL) says. “We now have a supergroup of three Copernicus satellites to spot super-emitters of methane very quickly and precisely identify the responsible facilities. Especially super-emitters in desert areas or extremely large emissions can be seen very well with these instruments, zooming in with increasingly high resolution. A fine example of very large but transient emissions that we could examine using the complementary observations happened along a Russian gas pipeline (see figures). In our paper we show that Sentinel-3, combined with Sentinel 5P and Sentinel -2, is a great asset for methane mitigation.”

Figures (see above):
The tiered use of the three satellites starting with a Sentinel-5P observation on 18th June, 2021, that shows a clear methane plume in Russia. Zooming-in with Sentinel-3 shows that there are actually two methane plumes coming from the locations indicated with the white crosses. Further zooming-in with Sentinel-2 clearly shows the leaks originate from two facilities along the gas transmission pipeline.