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A World of Water, Seen From Space


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.”

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."

So the GPM project represents a surprising innovation, given that it's 2014 and that, with the help of satellites, we can see space-taken snapshots of our own houses with the click of a button. "It's the first time,” Peters-Lidard notes, that “we can see water drops all around the world.”


The idea of using satellites to understand the Earth’s weather patterns is older than NASA itself. The basic notion—sending cameras into orbit to observe those systems from above—dates back to the V-2 rocket launch of 1946; by 1958, the Army Signal Corps had developed early prototypes for objects that would take imagers into space for long duration. The first weather satellite, Vanguard 2 (designed to measure cloud cover and resistance), was launched in1959. It was unsuccessful, however. A poor axis of rotation, as well as an elliptical orbit, kept it from collecting much useful data. But the first successful weather satellite came soon after:  Tiros-1, launched by NASA in April of 1960, operated for 78 days. It was followed by NASA’s Nimbus program, which paved the way, in turn, for most of the Earth-observing satellites NASA and NOAA have launched since then.

NASA sees its challenge now as putting those observations into a slightly more cosmic context—for itself, and for the public. As James Garvin, chief scientist at the NASA Goddard Sciences and Exploration Directorate, puts it: “How do we understand how we change over time, over scales that we care about?” 

Given the weather results of climate change, the need to (as NASA puts it) “improve the techniques of predicting and preparing for abnormal weather” is urgent. And GPM will, the agency says, “set a new standard for precipitation measurements from space.”

GPM is an outgrowth, most recently, of TRMM, the Tropical Rainfall Measuring Mission, which launched in 1997 with a three-year mandate. As sometimes happens, the vehicle outlived its expected shelf life; fourteen years after its planned expiration date, TRMM is still operating. Which is a good thing. But TRMM, as its name suggests, focuses on the rainfall around the equator. It covered an area that stretched from the 35th parallel north to the 35the parallel south—so, with it, as Peters-Lidard puts it, “we really were focusing on measuring the tropics.” GPM, however, covers an area stretching from 65 degrees north to 65 degrees south—all the way up and down, in other words, to the poles.

By expanding its observation areas to those latitudes, GPM will be able to make more accurate and frequent observations of tropical rainfall—but it will also be able to extend its vision to include the snowfall and light rain that are common in non-tropical areas of the Earth.  

Getting such a comprehensive view of the planet's water required an international collaboration—one that was more than a decade in the making. JAXA, the Japanese space agency, oversaw the launch of Core as well as the development of the satellite’s DPR instrument. It developed that instrument in consultation with the National Institute of Information and Communications Technology (NICT). NASA developed Core’s bus (its basic infrastructure) and its microwave radiometer. But other agencies contributed, as well, both to Core and its network of fellow satellites: the French space agency (CNES), the Indian Space Agency (ISRO), the European Organization for the Exploitation of Meteorological Studies (EUMETSAT), the U.S. Air Force Defense Meteorological Satellite Program (DMSP), and, of course, NOAA.

The engineer Paul Richards, who traveled to space in 2001 for the STS-102 Discovery mission, points out how much work is involved not just in launching a spacecraft, but in coordinating that work among agencies that are scattered across the globe. “Twelve years ago, I worked a little bit on GPM,” he says. To make something of that scope come together, “it takes 12 years and thousands of people.”


The hope is that many more thousands of people make use of the data GPM provides. "One of our jobs as NASA scientists is to make our satellite data useful,” Peters-Lidard says. That includes converting those data into “products”—images, videos, databases, and the like. The information from the satellites, Kidd explains, “is transmitted in real time across a communications network and gets translated to Goddard, where they do the processing. They take that information and combine it with other information you get from other satellites.”

And they take that, in turn, and post it to the web.

"It's quite a big journey for the data,” Kidd points out. By the time the information has reached the public, it has traveled "through thousands of miles of communication networks."

So what will all that long-journeying information be used for, ultimately? To better predict hurricanes, for one thing. And to understand flooding patterns along rivers. And landslides. This knowledge can, in turn, be applied to our understanding of agriculture—not to mention famine. And drought. Peters-Lidard, as part of her work with NASA, collaborates with USAID. And “we use NASA's precipitation data,” she says, “to predict where drought and famine might occur and make more informed decisions about aid.” It's an actuarial approach to the Earth's resources, facilitated by images taken from space. 

GPM's Applications Specialist, Dalia Kirschbaum, anticipates a similar use case. “I am also particularly excited about GPM," she wrote in an email, "because my research focuses on rainfall-triggered landslide modeling, which requires key precipitation inputs such as TRMM provides and GPM will provide." And that, she notes, will help scientists like her "to accurately estimate where and when landslides may be occurring all over the world." In places including, but certainly not limited to, southern California.


The implications, as NASA sees them, also translate to places that are slightly farther afield. "It's our job to put our Earth in the context of the wider universe," James Garvin says. “If we don't understand how we work, how are we going to understand how Mars works? Or how Venus works? Or planets orbiting around other suns?” 

The tension embedded in terms like “weather patterns” and “climate change” bring an inevitable political dimension to the GPS products and the work that goes into creating them. “It's not just about the science,” says Jack Kaye, associate director for the Research of the Earth Science Division within NASA’s Science Mission Directorate. “We have the availability and the opportunity to make that information available” to the public, he says of the GPM products. And the public in turn, he hopes, can use that information to “make good decisions.”

The global scale of the project means that the “public” in question here is not merely the American version. With GPM, the world is flattening—at least when it comes to its understanding of its own crucial hydration systems. What we will be getting as a result of that little system of satellites hanging out above us is a constantly-updating snapshot of all the water, in all its forms, across the world. Those snapshots will be shared. “The data are just as good anywhere in the world as they are here,” Kaye says, from a building in Maryland. “If you think about it, that's unique in human experience.”

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