New NASA Satellite Would Observe Global Rainfall

Precipitation could finally be measured from space rather than the ground.

What's 39.3 feet long, weighs 8,598 pounds and can see raindrops from space?

NASA's new rain and snow satellite, which will launch from Japan in a month.

The satellite is called the Global Precipitation Measurement Core Observatory, or GPM, and is the first satellite to offer a near-global picture of rain and snowfall over the Earth.

"Rain and snowfall affect our daily lives in many ways. ... Extreme precipitation events like hurricanes, blizzards, floods, droughts and landslides have significant socioeconomic impacts," Steven Neeck, deputy associate director of the NASA Earth Science flight program, said at a media briefing held yesterday.

"GPM, through its core observatory and constellation of satellites, will dramatically improve our knowledge of global precipitation and our ability to forecast it and its consequences," he added.

Many developed countries such as the United States and much of Europe have ground-based instruments to detect and measure rain and snowfall.

But in much of the world -- over the oceans, in developing nations and near the poles -- measurements of precipitation are few and far between, or even nonexistent.

The GPM satellite has its own dual-frequency radar instrument to measure rainfall but will also use radar instruments on existing satellites (they include satellites from other countries as well) to gather information about global precipitation.

It also has a microwave imager that can see the precipitation in all layers of clouds.

Gail Skofronick Jackson, a GPM deputy project scientist at NASA's Goddard Space Flight Center, said the satellite will be able to see through clouds in three dimensions, like a CT scan, as well as all the way through the cloud, like an X-ray.

Prompt information could save lives

Once the satellite is launched in late February and completes a 60-day checkout period, the data it collects will be made available for public use every three hours. This could provide a lifesaving capability, NASA scientists said.

"Can you imagine if flood forecasting and landslide forecasting had estimates within three hours after data collection, every three hours, all day long? That means that the emergency planners can evacuate if necessary," Skofronick Jackson said.

Climate researchers will also be able to use the precipitation information gathered by the satellite, whose latitudinal range extends from 65 degrees north to 65 degrees south -- from far northern Alaska down to the Antarctic peninsula.

"Currently we have very little information from ground-based measurements over the interior continents like Canada, Siberia and especially over the high-latitude oceans," said Steve Nesbitt, an atmospheric scientist at the University of Illinois who will be using data from the satellite once it is launched.

"It's kind of like a black hole for precipitation."

Gaining access to rain and snowfall data in these far-flung locales will help researchers improve climate models, Nesbitt said. Polar researchers will finally be able to have data on how much it is snowing and where.

Data from the satellite may also help improve spring runoff forecasts in places like northern Canada, parts of the Alps and in the U.S. West, where snowmelt plays a key role in providing water for the rest of the year.

"It's true in the United States we have a pretty extensive distribution of snowfall measurements in the Rockies, but even with hundreds of stations, GPM is going to have such high resolution that we can really start to drill down into different areas that we haven't before," Nesbitt said.

Flood of new data for climate models

Christopher Williams, an atmospheric scientist at the University of Colorado, Boulder's Cooperative Institute for Research in Environmental Sciences, has been working with NASA researchers to improve how climate models represent rain processes.

So far he's used data from the Tropical Rainfall Measuring Mission (TRMM), a NASA satellite that launched in 1997. But TRMM only measures rain in the tropics. Now Williams will be able to work with modelers to globally improve how they represent rainfall.

He does this by comparing model runs with real-world measurements. If, for example, the model predicts heavy rainfall when it actually only drizzled, Williams works to help modelers tune the models and figure out what their algorithms might be missing.

The new precipitation satellite, a collaboration between the Japanese Aerospace Exploration Agency, known as JAXA, and NASA, has been a work in progress for more than a decade. Although its design life is just three years, it has enough fuel to last 12 or 13 years, and NASA officials hope it will work for at least five.

The GPM launch is scheduled for between 1:07 and 3:07 p.m. EST Feb. 27 from JAXA's Tanegashima Space Center in Japan.

Illinois' Nesbitt was in graduate school when TRMM, the first precipitation satellite, launched. Having watched its progress for most of his career, he sees the launch of GPM as a moment for celebration. Nesbitt is planning to have a party to watch the takeoff live.

Williams was also excited about the impending launch and said the buildup to it was "nerve-wracking." "We've been talking about this for years now, and it's finally a month way," he said.