A World of Water, Seen From Space

Space agencies across the planet launch the most ambitious plan yet to understand how the world's water works.
The GPM Core satellite launches from Japan on Thursday, February 27. (NASA)

Late last week, from a launch pad at the Tanegashima Space Center in southern Japan, a rocket shot toward space. Nestled inside it was an amalgam of solar arrays and communications equipment and propulsion instruments, all of them cobbled together in the utilitarian-chic manner favored by aerospace engineers—one more satellite for the growing constellation of man-made objects sent to orbit, and observe, the Earth.

NASA calls this latest satellite the Global Precipitation Measurement Core Observatory. I propose we call it, to make things simpler for ourselves, “Core.” Core is, technically, a weather satellite, built to observe the workings of the Earth from beyond its bounds. But it’s more complex than a traditional satellite: Core gets its name from the fact that it is the central unit in a network of nine satellites studded across the exterior perimeter of the Earth, contributed to the cause by various countries and space agencies.

Their job? To analyze the planet’s water, from beyond the planet. The Global Precipitation Measurement project, with Core as its central piece of orbiting infrastructure, will provide observations of the world’s snowfall and rainfall and cloud patterns, across a network, at three-hour intervals.

As Chris Kidd, an associate research scientist at NASA who oversaw some of the data infrastructure for GPM, explains it: “If there's any clouds or precipitation, that alters the signatures—so being able to use that information, we know where the clouds are. We know where the rain is." 

And we can see the rain, and everything else, in 3-D—"so if we have a big thunderstorm," Kidd says, "we can see it in three dimensions.” And, Dorothy-from-Twister-style, “we can actually probe inside it to see the actual different particles within the thunderstorm.” This, in turn, can provide data—more data than we already have—about how these systems develop.

A visualization of the GPM Core Observatory, with partner satellites visible in the background (NASA)

Christa Peters-Lidard, a scientist at NASA Goddard’s Hydrological Sciences Laboratory, explains it like so: “It’s almost like taking a CAT scan of clouds."

***

To understand why space agencies have invested in this high-tech form of cloud-watching, you can look to, among many other places, the American west. Late last week, southern California was hit with a powerful rainstorm—the biggest one to hit the area in nearly three years. This might have been good news for a drought-ravaged section of the country. But the rain that pounded Los Angeles and its environs didn’t merely bring much-needed moisture along with it. It also brought landslides. And power outages. And, as one news outlet put it: “flooding, evacuations, [and] scenes of disaster.”

Vehicles drive through a rain-flooded portion of the Interstate 5 freeway in Los Angeles on March 1. (Reuters)

The storm also brought a reminder of a troubling fact: We don’t fully understand how water works. We understand the stuff, of course, on a molecular level (H2O!). We understand it, generally, on a biophysical one (8 glasses a day! Maybe!). We understand that it is, in a profound and also totally basic way, essential to our existence. Which is why, as we search for life on other planets, we look not for that life itself, but for evidence of water.

But water, as swimming pools and motion-activated faucets and the existence of Sno-cones can make it easy to forget, is not just stuff that keeps us clean and amused and awed and alive. It’s also a system, a complex of chemical interactions closed and contained within the delicate little globe that also happens to contain the rest of us. And in that sense, the systemic sense, water remains something of a mystery. How do clouds form, actually? How much water is contained within Earth’s soils, ultimately? How does water affect climate—and how will climate change affect the world’s water?

***

To answer those questions, you need the right equipment. Core is the latest in a long line of weather satellites; part of what distinguishes it from the others is the range, and complexity, of its imaging instruments. Chris Kidd is from the United Kingdom, where moisture tends to be both diffuse and relatively constant, covering Earth's surface in the form of fogs and light rains. He contrasts his country's climate with that of tropical rainforests, where rain is periodic and, as physical droplets, relatively large. It takes different instruments to capture, from space, these variations. Add to that the demands of imaging the clouds that cover Kansas, and the snows that cover Antarctica ... and you need a series of different instruments that operate, much like the space agencies that are cooperating for GPM, in unison. 

The GPM constellation, as a rendering (NASA)

Core carries both a dual-frequency precipitation radar (acronym: DPR) and a microwave radiometer. The constellation of satellites it communicates with carry similar microwave radiometers—which allows them to talk to each other, essentially, across space. “The radar on the GPM Core Observatory is unique,” Peters-Lidard says, “and that's what gives us that detailed picture. But the microwave imager allows us to connect with all those other satellites so we can produce global maps of precipitation every three hours, everywhere where our orbit sees."

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Megan Garber is a staff writer at The Atlantic. She was formerly an assistant editor at the Nieman Journalism Lab, where she wrote about innovations in the media.

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