CloudSat Takes Flight

meet graeme stephens: the mind behind this groundbreaking cloud surveillance satellite

by heather hawkins

In a tree-lined, college town commonly known for complex microbrews and students studying to be large-animal vets, the story of a CSU atmospheric science professor and a multimillion-dollar weather satellite may sound a bit like fiction.

It’s not.

Professor Graeme Stephens, a team of experts, the government and others are currently banking on a $217 million satellite called CloudSat to help weather watchers better study causes surrounding global warming and better predict flooding and drought.

If evidence from the last few months is any indication, the satellite – hurled into space in late April from Vandenberg Air Force Base on the central California coast – has been successful at using radar to dissect clouds in the sky and beaming those images back to scientists on Earth.

So what do the bowels of a cloud tell us?

“If you’re concerned at all with the effect that human contributions have on green house gases, then you’ll want to know the role that clouds play,” Deborah Vane, CloudSat deputy principal investigator at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, Calif., explained in a recent telephone interview.

Many people don’t realize the important role that clouds play in Earth’s climate. Clouds regulate heat in the atmosphere and on the planet, but little is known about how that occurs. The CloudSat mission will provide new measurements of this process, providing details about basic cloud components such as water content, ice content and the origin of clouds.

The satellite, roughly the size of a small car, resembles a bumble bee with a round, plump body and large rectangular wings reaching from head to toe. Stephens, a professor in the Department of Atmospheric Science, said his idea for CloudSat “germinated in the late 1980s and began to take shape as a concept in 1993.”
Five years later, Stephens proposed his idea for two cloud-studying satellites to NASA. The proposal “to provide observations necessary to advance our understanding of cloud abundance, distribution and structure” was accepted in 1999 under NASA’s Earth System Science Pathfinder (ESSP) program, according to CSU’s CloudSat website.

CloudSat and CALIPSO, formally known as Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations, were split into two separate missions. CloudSat is lead by Stephens and others at CSU, and CALIPSO is lead by NASA.

As principal investigator of the CloudSat mission, Stephens is responsible for distributing data to the world. He and other scientists at CIRA, the Cooperative Institute for Research in the Atmosphere on the Foothills Campus at CSU, process CloudSat data. The data is then sent to the scientific community and is available for public view on the Internet. Stephens also oversees the science behind CloudSat.

It only seems right that Stephens is leading the CloudSat mission, as he is “a leading authority on the study of atmospheric radiation, remote sensing and climate change,” said Paul Miller in a fall 2005 CSU Alumni magazine article titled “His Head in the Clouds.”

$185 million bucks

The ESSP program was started in 1996 to sponsor missions designed to address specific, highly focused scientific issues. The program supports a variety of scientific objectives related to Earth science, including studies of the oceans, land surfaces, polar ice regions and the atmosphere, according to a NASA press release.

Despite its larger aim, such a complex, detailed mission has had its share of problems. It took NASA’s JPL and the Canadian Space Agency longer than the planned three-and-a-half years to build the radar, which slowed the completion of the spacecraft and launch vehicle at Ball Aerospace and Technologies Corp. in Boulder.

CloudSat, funded with $185 million taxpayer dollars, was scheduled to launch six times before the successful launch in April, nearly six months after its completion. The first six attempts were scrubbed due to complex technical and scheduling issues, Stephens said.

Since its launch, however, the spacecraft has been working near perfect, Stephens said. The first images of a warm storm front over the Norwegian Sea were received from CloudSat during a system test on May 20. The images show multiple cloud layers that were previously inaccessible.

 “CloudSat’s radar performed flawlessly, and although the data are still preliminary, it provided breathtaking views of the weather on our planet,” Stephens said.

Flying 438 miles above us, CloudSat operates 24 hours a day, seven days a week. The three square solar panels on either side of the spacecraft absorb energy during the sunlit portion of its orbit and store power in the batteries when it is in the eclipse, Vane said.

CloudSat flies close to Earth’s North and South poles in a nearly circular orbit. Flying at seven kilometers per second, it will go around Earth every 99 minutes and will repeat the same ground track every 16 days, according to CSU’s CloudSat Web site. 

Scientists at Kirtland Air Force Base in Albuquerque, N.M., send commands up to a small computer on the spacecraft telling it when to receive data, Vane said. Data is transmitted from the spacecraft about 10 times per day, making data available every two to four hours.

“The spacecraft generates short pulses of electromagnetic energy that are sent down through the atmosphere. Those pulses are just the right size that they interact with water and ice particles within clouds,” Vane said.
The pulses are reflected back to a receiver on CloudSat. The time delay from when the signal leaves CloudSat until it returns indicates the distance the wave traveled. Not all waves reflect off the cloud particles; some make it all the way to the ground before returning. Time delay and the strength of the returned signal are recorded, revealing the characteristics of the clouds that lie below. A multi-colored, vertical map of the clouds is then created based on the information CloudSat receives.  But how do the waves know if they hit ice or other particles?

Clouds as 3-D images

CloudSat uses millimeter wavelength radar – think the thickness of a dime – over 1,000 times more sensitive than existing weather radars. Other radars use centimeter wavelength – just larger than a yellow No. 2 pencil- that can only detect raindrop sized particles on the top or bottom of the cloud. CloudSat’s radar allows it to detect much smaller particles of water and ice throughout the entire cloud.

This is important because clouds are composed of tiny water and ice particles that have not been detected by existing radars. The number and size of particles depends on the amount of water vapor, the gas form of water, in the air and the number of tiny aerosols, minute airborne particles, available to act as seeds for cloud formation.
 As aerosol concentration increases within a cloud, water in the cloud is spread out over many more particles. This decreases the size of the particles. Smaller particles fall more slowly in the atmosphere and decrease the amount of rainfall. This is because smaller particles do not become saturated and fall from the clouds. Decreased rainfall can cause problems for humans because freshwater becomes scarce. Two-thirds of the freshwater on Earth is unusable because it is locked away as ice in polar regions of the globe. Accessible freshwater must be replenished to sustain life, and clouds are a key component in replenishing the water. Salt water in the oceans evaporates, condenses into clouds, precipitates as rain and snow then returns to the oceans.
Although there are numerous weather radars in existence, they fall short of explaining how clouds truly affect Earth’s climate.

“Climate observations have been relatively primitive until now,” said Stephens, “but CloudSat will help to fill major observing gaps.”  

The 3-D images produced by CloudSat give scientists a vertical look at cloud properties across the globe. They reveal multiple cloud layers of water and ice. Instead of looking at the overhead view of circular, white, “cotton candy” clouds on the weather channel, we can see images similar to the layers of a club sandwich. Or as Stephens explains it, “like a CAT-scan.”

“We’re seeing the atmosphere as we’ve never seen it before,” said Vane. “We’re no longer looking at clouds like images on a flat piece of paper, but instead we’re peering into the clouds and seeing their layered complexity.”

With the radar that CloudSat uses, scientists will create much-needed climate models and will be able to predict where and why clouds and precipitation form. This will give them a better understanding of how the water cycle works. Scientists are hopeful that this will improve weather forecasts and increase the accuracy of storm warnings in addition to increasing knowledge about global warming.

“Getting this historic data is a step toward the way the atmosphere will be observed in the future,” Stephens said. “CloudSat has created an avenue for research worldwide.”

Hail CALIPSO

In addition to CloudSat, CALIPSO, a satellite designed to study aerosol content in the atmosphere, was launched on the Delta II rocket built by Ball. CALIPSO will help scientists understand how clouds are formed and what happens as humans release more and more aerosols into the air; by burning coal and oil, for example.

CloudSat and CALIPSO will join three other satellites as part of NASA’s “A-Train” constellation, a nickname given to the group of satellites because they fly close together. The spacecrafts had to be launched during a particular instant on any given day in order to get the right orbit around Earth and to adjust to the A-Train orbit, CSU’s CloudSat Web site reports.

All five satellites will observe aspects of Earth and its atmosphere. The information gathered by these five satellites will give scientists the most advanced set of observations of the Earth’s atmosphere to date. Combining the data from the five satellites will help to improve climate models and create a better understanding of global climate change.

Scientists from Canada, France, Japan, Germany and the United States have contributed their facilities and expertise to the CloudSat mission. 

“It’s been an amazing journey to get to this point,” Stephens said. “The partnerships and teamwork have been unbelievable.  There’s been quite a lot of dedication from everyone.”

CloudSat is funded by NASA to collect data for two years to observe more than one seasonal cycle. However, there is no technical reason why the mission could not last longer, as the radar was designed to last a minimum of three years.

“If the instruments are working fine, the mission is likely to be continued,” Stephens said.

           

View CloudSat images on the web

All of the images from CloudSat can be viewed at www.cloudsat.cira.colostate.edu by clicking on the “Latest Quicklook Images” link and selecting one of the orbits. A larger, more detailed image is shown when you click on the colored frame number. Orbit 654 on June 12 shows tropical storm Alberto off the coast of Florida in frame 29. CloudSat shows that the storm is about 16 kilometers (10 miles) high. The red colors of the storm represent highly reflective particles like rain or snow, and the blue indicates thinner clouds. The blue line at the bottom of the image indicates that the clouds are over water and the brown line indicates land.