资源环境科技发展态势分析平台

In December 2016, soon after advisers to President Donald Trump threatened to shut off NASA’s climate-observing satellites, California Governor Jerry Brown made a famous promise: “If Trump turns off the satellites,” he said while addressing a geoscience meeting, “California will launch its own damn satellites.” That promise is now a reality, with California and partners set to launch by 2023 two satellites to spot and monitor plumes of planet-warming carbon dioxide (CO₂) and methane. If all goes right, dozens more could follow.

The $100 million Carbon Mapper project, announced today and financed by private philanthropists including Michael Bloomberg, will advance efforts to track concentrated emissions of greenhouse gases, which rise from fossil fuel power plants, leaky pipelines, and abandoned wells. Previous satellites have lacked the resolution and focus to monitor point sources rigorously. “We’re going after the big emitters,” says Riley Duren, Carbon Mapper’s CEO and a remote-sensing scientist at the University of Arizona. He says the ultimate goal is to be “like the weather service for methane and CO₂.”

The announcement has the potential to “shake up” the field of greenhouse gas monitoring and verification, says Ray Nassar, an atmospheric scientist unaffiliated with the project at Environment and Climate Change Canada. He says the satellites would be immediately useful for tracking fugitive methane emissions, which have more than 80 times the warming power of CO₂ emissions in the short term. “Finding, pinpointing, and stopping the big leaks is thus key,” he says.

The satellites will be built and managed by Planet, a California company that already operates a constellation of Earth-imaging satellites. The spacecraft will rely on “hyperspectral” imaging spectrometers developed by NASA’s Jet Propulsion Laboratory (JPL). Rather than gathering light in just a few discrete wavelength channels, like the human eye, these spectrometers capture reflected sunlight and subdivide it into more than 400 wavelength channels across the visible and into the infrared. The intensity of light across these channels can be tied to specific chemistries and reflect the abundances of certain gases in the air molecules below. “It’s a molecular mapping system,” says Greg Asner, an ecologist at Arizona State University, Tempe, who will lead many of Carbon Mapper’s scientific applications.

The satellites won’t just measure gases in the air; they will also detect chemical signatures on the ground. By measuring the intensity of green chlorophyll or detecting the signatures for excess salts or fungus, for example, researchers will be able to evaluate the health of crops and forests. They can prospect for minerals in remote regions. They can map and identify different coral and algae species, and they can track dust and soot. Even snow and ice pops out in these sensors, says Robert Green, a remote-sensing scientist at JPL. “Snow is one of the most colorful materials on Earth if you look beyond visible light.”

Scientists have dreamed for years of getting hyperspectral sensors into space, with few successes. It is difficult to build instruments that yield identical results, and hard to collect enough light at orbital speeds to detect the fine signals of methane, CO₂, or chlorophyll. But over the past decade, Asner, among others, has demonstrated the capabilities of a JPL-built hyperspectral instrument as part of his Global Airborne Observatory, measuring biodiversity from aircraft. Similar instruments will go on the Carbon Mapper satellites. NASA also plans to launch and mount one on the International Space Station in 2022, and will most likely put one on one of its next major Earth-observing satellites, launching later this decade.

The sensors can reliably catch CO₂ and methane plumes, which was unexpected, Green says. “People didn’t believe you could do this.” Until now, satellites tracking CO₂, like NASA’s Orbiting Carbon Observatory-2, have used sensors that target narrow bands of light where there is a strong absorption signal from the gas. But in the broader bands gathered by the JPL instruments, plumes kept popping up—from power plants, natural methane seeps, and even remote pipelines that leaked secretly from grassy fields. That led to aircraft campaigns that targeted these emissions in recent years, Asner says. “We call it the killer app for spectrometers.”

The first two Carbon Mapper satellites will each be roughly the size of a washing machine, weighing up to 200 kilograms. They will provide imagery with a resolution of 30 meters but won’t offer global coverage at first. Instead, they will target regions known to host superemitters, like power plants, oil and gas drilling, or livestock operations. The regions will be revisited every few weeks to start. All emission data, calculated from the plume intensity and length, will be made publicly available—in the hopes that governments and businesses will do more to staunch leaks and tamp down discharges. “We call it map and cap technology,” Asner says.

Over the past few years, California officials have helped develop tools to take advantage of the satellite data. They will the state step up its methane monitoring—and enforcement, says Jorn Herner at California’s Air Resources Board, the state regulator. Currently, their program might require a ground-based inspection for methane emissions every 3 months. Satellites that can revisit a site every week or so, checking for problems and confirming that leaks are repaired, will help immensely, Herner says. “If you have an eye in the sky, the efficacy of our requirements goes up significantly.”

Carbon Mapper is not the only greenhouse gas monitoring satellite being built by nonprofits. The nonprofit Environmental Defense Fund is building MethaneSAT, which will focus exclusively on methane. MethaneSAT, although less sensitive to individual plumes, will be more capable of capturing a regional picture that includes numerous sources of low concentration, like the methane that burps out of rice paddies. The two systems are “perfectly complementary,” Duren says.

Should Carbon Mapper’s first two satellites prove successful, Planet envisions building a commercial constellation of similar satellites that would revisit every spot on the planet once a day, and selling those data to regulators and companies. It would be a scientific windfall for many disciplines, with free data for scientists to access through Planet’s standard research program. Asner, for example, spent 3 years using aircraft to map the biodiversity and health of forests in Peru through subtle variations in chlorophyll and other nutrients. “What took me 3 years will get down to a week,” he says. “This is the future.”