An interview with Beth Weinstein, a GPM integration and test (I & T) engineer, Lisa Bartusek, GPM Deputy Mission Systems Engineer, and Carlton Peters, associate branch head at NASA Goddard Space Flight Center and the GPM thermal branch development lead. These engineers are all part of the larger integration and test team that put the spacecraft through its paces and prepares it for launch.

Researchers need accurate and timely rainfall information to better understand and model where and when severe floods, frequent landslides and devastating droughts may occur. GPM’s global rainfall data will help to better prepare and respond to a wide range of natural disasters.

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Dalia: GPM will help us to understand precipitation extremes. And this is everything from too much rainfall, such as flooding in India or Southeast Asia, to too little rainfall such as drought in the U.S. Southwest.

Eric: There's about one major flood a day someplace in the world, so it's not as if it's a rare event. A big problem is that over much of the world the in situ data, the gauges, and the measured precipitation just isn't available. To predict floods you need to have the data in near real-time. And so the satellites are about the only way--GPM is about the only way--that this is going to happen. And so we're going to use GPM rainfall retrievals to go do analyses, do flood forecasting, and bring climate services, bring information, to users in these areas.

Dalia: Landslides happen all over the world in nearly every country, and they cause more economic damage and more fatalities than people generally think. The large majority of landslides around the world are triggered by intense or prolonged rainfall. A landslide is a general term, often used for mudslides, debris flows, rock falls, and usually it's just a mass of rock, earth, and dirt basically moving down a hillslope. Typical landslide studies are done at the local scale and they use gauge data. Now this is a problem in areas of topography where we don't have gauges or radar, in particular in developing areas where we don't have any information. So satellite data is really important for understanding where and when this intense rainfall might happen that could trigger landslides.

Tom: In the western U.S. we deal with drought on a regular basis. It tends to be cyclic. We'll get two or three dry years and we'll get a few wet years. If somebody could predict when the dry ones are coming, we'd be a lot better off. A lot of our water here comes in snow It accumulates up in the mountains in the wintertime, runs off in the spring, and that's we use for irrigation in the western U.S. 

Wade: Agricultural drought is defined as a lack of water within the top meter of soil for adequate crop functionalities, adequate crop productivity. And if you're talking about agricultural drought, probably the biggest error source is the quality of the precipitation information that you have available. If you have good precipitation information, you can do a very good job of characterizing drought and often its subsequent impact on agricultural productivity.

Tom: We do work in research in determining the water needs of crops and what the impacts on crops are if you don't have enough water. We're doing this because we realize that in the western U.S. there will likely be less water available in the future than there has been in the past, and the farmers need to know how to respond to that decreasing water supply. Certainly when we're looking nationwide, the better prediction we have of how much rain we've been getting and how much is likely to come in the near future is very, very important. To the extent that we can predict that with satellites, it's really beneficial. This isn't just a U.S. problem; it's a global problem. Many countries of the world are facing the same kind of issues that we are. And so we expect this information to be able to be used in the east and the western U.S. and globally.

Dalia: We need accurate and timely rainfall information to understand disasters like floods, droughts, and landslides. GPM's global rainfall data will help us to better understand and model these types of disasters around the world.

GPM Takes Rain Measurements Global

As anyone who has ever been caught in a sudden and unexpected downpour knows, gaps still exist in our knowledge about the behavior and movement of precipitation, clouds and storms. An upcoming satellite mission from NASA and the Japanese Space Agency aims to fill in those gaps both in coverage and in scientists' understanding of precipitation. 

The Global Precipitation Measurement, or GPM, mission will set a new standard for precipitation measurements from space and it's doing so by joining forces with countries around the world, keeping not just one satellite's weather eye on the horizon, but nine.

"We need virtually continuous observation everywhere to construct a complete picture of precipitation around the globe, and that requires a lot of resources," says Arthur Hou, GPM project scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. "Precipitation does not recognize national boundaries. It is in the best interest of every nation to pool resources together to make the best possible measurements through partnership."

For the GPM mission, NASA and the Japan Aerospace and Exploration Agency (JAXA) are joining forces with the space agencies of France and India, as well as the operators of meteorological satellites in Europe and the United States. The eight partner satellites on the mission are called the GPM constellation.

Illustration of the multiple precipitation measurement satellites which comprise the GPM constellation. Credit: NASA

"Each of the constellation members has its own scientific or operational objectives, but they all contribute data to GPM to create a unified global precipitation data product every three hours," says Hou.

At the center of this effort is the GPM Core Observatory, a satellite that will unify all the measurements from the constellation. The high quality measurements made by the GPM Core Observatory will serve as a reference standard for improving the accuracy of precipitation measurements made by other satellites. 

Building on the success of the NASA and JAXA Tropical Rainfall Measuring Mission (TRMM), GPM carries two instruments. The GPM Microwave Imager (GMI) —provided by NASA—will estimate precipitation intensities from heavy rain, light rain and falling snow by carefully measuring the minute amounts of energy naturally emitted by precipitation. The Dual-frequency Precipitation Radar (DPR)—provided by JAXA—will make detailed measurements of three-dimensional rainfall structure and intensity. Together the two instruments will combine with the Core's near-global coverage of Earth and data from the constellation satellites to give a more complete picture of global precipitation.

Pole-to-Pole Coverage

The GPM Core Observatory is being built and tested at Goddard Space Flight Center. The silver disc and drum (center) is the GPM Microwave Imager, built by Ball Aerospace Corp, in Boulder, Colo. The large blocks on the base is the Dual-frequency Precipitation Radar, built by JAXA. The tall golden antenna is the High Gain Antenna for communications. Credit: NASA

GPM's predecessor, the TRMM satellite, revolutionized scientists' view of precipitation with its highly sensitive and high-resolution observations. But TRMM was designed to measure moderate to heavy rainfall over the tropics, from 35 degrees latitude North and South of the equator. Most of Europe, the northern portion of the United States, Canada, and Japan are outside of TRMM's view. When launched, GPM's coverage will expand beyond TRMM's into those mid and high latitudes. Its orbit from 65 North to 65 South will mean measurements of precipitation across 90 percent of Earth's surface, from about the Arctic Circle to the Antarctic Circle.

Expanding coverage also means expanding the types of precipitation that GPM will measure, most notably light rain and snowfall. They account for about half of the precipitation in temperate mid-latitudes and cold high latitudes and are major contributors to freshwater resources in places like the United Kingdom and northern Europe, the southern Appalachian Mountains and the snow packs of the Rocky Mountains and the Sierra Nevada.

Measuring snow and light rain from space is a technical challenge because of their small size, and the multitude of shapes of ice crystals, says Gail Skofronick-Jackson, GPM's deputy project scientist at NASA Goddard and a specialist in detecting snow from space. 

The advancements on the GMI radiometer include an increased sensitivity to light rain and for the first time snowfall, and the two radar channels on the DPR will provide information on the size and shapes of raindrops and snowflakes, which will improve estimates of how much water they hold. "We're very excited about this new capability," says Skofronick-Jackson.

The new data on light rain and snow, like all the measurements GPM will make, won't just affect the weather forecast. They will also improve what climate modelers can say about the distribution of rainfall in the coming years. "As the Earth's temperature warms, most models predict that we'll have more heavy rain events, but they disagree on whether we'll have more or less light rain," says Hou. "GPM data will help us to clarify that."

A Song of Water and Heat

Storms over the cloud radars during the Mid-latitude Continental Convective Clouds Experiment. This experiment from April 22 to June 11 was part of the GPM missions ground validation program, where teams of scientists take very detailed measurements of rainfall and storm systems on the ground and compare them to measurements made by radars and radiometers similar to those that will fly on the Core Observatory. Credit: DOE/ARM/Scott Collis

As part of Earth's climate system, precipitation tells us about the ways energy moves around the planet. Hou says energy and precipitation are connected through the process of how water vapor in the atmosphere is converted into liquid or ice particles that make up clouds, rain and snow.

This process releases heat energy, called latent heat, into the atmosphere. You can see this happening in thunderstorm clouds; the release of heat causes air masses to rise and grow upward in a tall, billowing shape. This vertical movement of air masses creates pressure changes and wind -- ultimately influencing how large-scale winds circulate and transport heat around the globe, which then affects local climate. 

Precipitation at Earth’s surface is the signature of the total latent heat released throughout an atmospheric column above it. Scientists will use the combined moisture information from the GMI with the DPR's three-dimensional images of precipitation to get a better understanding of the mechanisms and behavior of latent heat structures that evolve with clouds and precipitation.

Now Presenting: Rain in 3D

Studying latent heat in storms dovetails with the direct need to study storm behavior, especially of hurricanes and tropical cyclones that can have devastating effects in terms of flooding, landslides, economic damage and loss of life.

The first space-borne precipitation radar on the TRMM satellite changed the way scientists understood storms. Its single radar frequency provided a new three-dimensional view of how systems like hurricanes grow and intensify as they move through the tropics. When the GPM Core observatory satellite launches, its DPR will have a second radar frequency that will not only add precision, but will also give scientists the ability to infer the microphysical processes that govern rain droplets and snowflakes within storm systems, including the process of condensation that produces latent heat. Additional heat accumulating high up in a storm is one of the signs that it's about to intensify, which is valuable information for forecasters.

Even more valuable will be the ability to continue to observe intense storms, like Superstorm Sandy, which devastated the New Jersey and New York coasts in Oct. of 2012, as they move north or south into the middle and higher latitudes. The GPM Core's expanded coverage will give scientists a window into understanding how individual storms like Sandy intensify and change over the course of their entire life cycles.

"Satellite data are already being used operationally to improve weather forecasts," says Hou. "GPM data will be of much higher quality and that will enable the operational agencies to continue to improve their forecast products."

GPM will also be used to improve other computer models, including those for understanding and predicting climate, floods, watershed hydrology, and crop forecasting. One of the moving parts they each depend on is accurate and frequent observations of rain, sleet, hail, snow and other forms of precipitation. Global GPM data will be part of fitting the puzzle pieces together.

"When most people start a puzzle, they do the edge pieces first. Other satellites have started that, but the GPM Core is really poised to complete the boundaries so we can understand how liquid rain and frozen precipitation fall out of clouds," says Skofronick-Jackson. The constellation observations fill in the rest of that puzzle, she says, "so that we have a complete understanding both scientifically and structurally of precipitation so we can apply it to all sorts of applications."

The GPM Core Observatory, the largest satellite to be built and tested at Goddard, will be transported from Maryland to Tanegashima Island in Japan where it will launch on a Japanese H-IIA rocket in early 2014.

Video Text:

The standing joke when scientists talk about understanding Earth's weather patterns in relationship to climate change is that they need to know three things for their models: precipitation, precipitation and precipitation. Scientists need more data, more frequently, over more of Earth's surface.

The short video "For Good Measure" explains why scientists turn to satellites to get a worldwide view of rainfall. Filmed at NASA's Goddard Space Flight Center in Greenbelt, Md., with a cast of more than 20 volunteers, the video walks through how rain touches our lives and how scientists plan to improve measurements with the upcoming Global Precipitation Measurement mission. The video can be downloaded in HD at: http://svs.gsfc.nasa.gov/vis/a010000/a011200/a011219/

Visualization of the GPM Core Observatory and constellation satellites.

The Global Precipitation Measurement mission, or GPM, provides the next generation of rainfall measurements from space. The mission is designed to tap into the observational power of nine independent satellites flying around Earth and combine their precipitation data into a single, global data set every three hours. With combined measurements, the GPM constellation becomes a powerful tool for observing rainfall worldwide.

Observing rainfall has become standard in our modern world. Where the rain goes, so too do the umbrellas -- and flood warnings, drought assessments, estimates for freshwater water reservoirs, long term planning for farmers, alerts for waterborne diseases, even famine early warning systems. Rain, snow, winter mix, hail and every other form of water falling from the sky touches everyone on Earth.

But the whole Earth surface is not covered by instruments to measure precipitation. Rain gauges collect precipitation in one spot that often represents huge areas. In the United States, for example, the National Weather Service maintains on average one rain gauge for every 400 square miles (about 20 miles apart). That's one point to represent rainfall, which is fine for looking at the regional picture, but not as good for covering the effects of individual rainstorms.

To measure and study incoming storms, meteorologists and scientists often use ground radar. Individual radars can cover an average area of 50,000 square miles (a range of 125 miles in each direction), and when combined with other radars in a network a more complete picture of the coming precipitation takes shape. However, even in countries with excellent radar coverage, gaps still exist, especially for higher altitude clouds that are out of reliable radar range and over mountain ranges that can block the radar signals.

In many places around the world, countries can't afford to have dense networks of rain gauges or radars, and so they often go without. Over the ocean, measurements from ships and islands are even fewer and farther in between. That's 78 percent of the world where we don't know, from the surface, how much fresh water is raining down into the salty oceans. And that means fewer data points for scientists to use to predict future weather and climate changes around the world.

Satellites fill in those gaps. Circling hundreds of miles above us, Earth-observing satellites take measurements of the whole globe. The GPM mission is based on the success of the Tropical Rainfall Measurement Mission, or TRMM. This pioneering precipitation satellite circles Earth at an angle that allows it to see all the rainfall in the tropics, an area between the latitudes of 35 north and 35 south, the southern border of Tennessee and about halfway through Argentina.

Example of precipitation data collected by the Tropical Rainfall Measuring Mission (TRMM).

Scientists wanting more observations combine TRMM's advanced rain data with data from other satellites that measure rainfall. This system allows them to increase the number of rainfall measurements over the course of a day and expand coverage to 45 degrees north and 45 degrees south (the U.S.-Canadian border and almost the tip of South America). But they still don't have a clear picture of higher latitudes toward the poles, especially areas that typically have light rainfall or snow that most satellites, including TRMM, cannot detect.

Enter GPM's Core Observatory at the heart of the new rain-monitoring constellation of satellites. It carries sophisticated instruments that can measure heavy tropical rains near the equator and detect light rain and falling snow near the poles. It will serve as a reference standard for all nine satellites and unify their measurements to provide a global precipitation data set that covers the area from the Arctic Circle to the Antarctic Circle (65 degrees north and 65 degrees south) every three hours.

The GPM mission was initiated by NASA and the Japan Aerospace Exploration Agency (JAXA), and also includes partnerships with the space agencies of France and India, as well as the agencies that operate meteorological satellites in Europe and the United States. NASA and JAXA are providing the GPM Core Observatory, which will launch from Japan in early 2014.

To download the video in HD, visit: http://svs.gsfc.nasa.gov/vis/a010000/a011200/a011219/  

Click here for a behind the scenes look at the making of "For Good Measure"

The cast and crew of "GPM: For Good Measure"

Video Text:

We plan our lives around rain. We always want to know when and where and how much. Not just for our weekend plans, but for how we make decisions about our safety and transportation, our economy, our livelihoods. So, how do we measure rain? Well, we can set out a rain gauge, like this one, and it measures the amount of rain that falls over time. The problem with this is that only measures rain in one very small spot. In fact, if you took all the rain gauges in the world packed them together, they would into two basketball courts. Now we can cover more ground if we use radar. Radar sends out a signal, and it measures how much of that signal is scattered by rain or snow. But radars are only available in certain parts of the world, and many countries just don't have access to that technology. And that's just on land. Think about how we're going to measure rain over all of the world's oceans. Look, the point is it's impossible to cover the entire Earth with enough instruments that are going to give us accurate precipitation rates for the whole globe. 

So, we have to think bigger and higher. Instead of having a patchy network of rain gauges and radars, we can have a whole constellation of satellites looking down at the Earth, measuring things like falling rain, snow and even ice. The Global Precipitation Measurement mission, or GPM, is going to do that. And it's going to give us precipitation rates for the whole globe every three hours. Now GPM is going to cover it all: from land and oceans, from the tropics to the edge of the poles, over mountains and valleys, from our farmland to our cities and towns. We're going to need more than a perspective on the ground if we're going to look at precipitation from a truly global standpoint, and GPM is just the mission that's going to give us that big picture.

This video (4:56) uses a combination of cartoon characters, a scientist, and a series of different Earth-observing satellites with data animations to teach the various parts of the water cycle.