Satellites Launched To Study Clouds
Saturday, April 29, 2006
NASA yesterday launched two long-awaited satellites designed to provide the first three-dimensional views of Earth's clouds and help predict how cloud cover contributes to global warming.
CloudSat and CALIPSO lifted off at 6:02 a.m. EDT aboard a two-stage Boeing Delta II rocket from the new Space Launch Complex 2W at California's Vandenberg Air Force Base. Sixty-two minutes later, CALIPSO separated from the second stage, and CloudSat followed 35 minutes after that.
The two spacecraft will stay in a "parking orbit" for up to a month while their instruments are checked, then join the "A Train" of Earth-observation satellites in polar orbit at an altitude of 438 miles. Scientific operations will begin in about six weeks.
CloudSat and CALIPSO -- for Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation -- were scheduled to launch in midsummer last year, but technical problems followed by a prolonged strike by Boeing aerospace workers delayed liftoff until April 21. A variety of communications, logistical and weather glitches scrubbed successive launch attempts for another week.
The two satellites, designed to image clouds from top to bottom, are the first Earth- or space-based instruments capable of viewing cloud layers and analyzing possible effects of the moisture and airborne particles within them on global weather and long-term climate patterns.
"It is important to understand how much water exists in clouds and how they are vertically structured," Colorado State University's Graeme Stephens, CloudSat's lead scientist, said at a pre-launch news conference. "The views of clouds we see today are two-dimensional, so we can't tell you [that], or what fraction of the moisture produces rain and snow."
CloudSat, a 1,870-pound spacecraft that cost $185 million, uses an ultrasensitive radar to send pulses downward into and through clouds. The pulses rebound from condensed water particles and ultimately from Earth, allowing scientists to map the clouds top to bottom -- not only for location but also for moisture content.
"Knowing the vertical structure is crucial" in learning about climate change, said Boston University climate scientist Bruce Anderson, who is not affiliated with the project.
Most scientists regard as "pretty solid" the evidence that human-induced emissions of carbon dioxide and other greenhouse gases are driving global warming, he said, "but the question is, how much?"
CloudSat will help answer that question. For the first time, scientists will be able to profile how low-level clouds reflect the sun's heat, dampening the effects of global warming, and how high-level clouds "trap" heat emanating from Earth, thus contributing to global warming.
"Every computer model predicts significant warming over the next 100 years, but is it going to be 3.5 degrees Fahrenheit, or 9 degrees Fahrenheit?" Anderson said in a telephone interview. "The uncertainty is due almost entirely to clouds, and the answer that CloudSat can provide is exactly the answer that scientists need."
CALIPSO, smaller than CloudSat at 1,294 pounds but more expensive at $223 million, carries three instruments. The primary one is a three-channel laser ranging device known as a lidar, which uses light pulses to profile cloud aerosols, tiny particles of dust and other materials floating in the atmosphere. These can be natural, such as smoke from volcanoes or dust kicked up by the wind, or human-induced, such as soot from power plants.
Some aerosols are reflective, helping dampen the effects of global warming; others absorb and hold heat, contributing to the greenhouse effect. In addition, water droplets in clouds form around aerosol particles, so the size and quantity of the particles help determine the amount of rainfall a cloud will produce, how reflective a cloud will be or even whether a cloud forms at all.
"CALIPSO will collect unique information," said CALIPSO lead scientist David Winker, of NASA's Langley Research Center.
CloudSat, followed 15 seconds later by CALIPSO, will be the second and third satellites in the A Train "constellation" of Earth observation satellites led by NASA's Aqua, and including France's PARASOL and NASA's Aura. "A" in A Train stands for "afternoon," because the constellation crosses the equator every day at 1:30 p.m.
CloudSat is designed to operate for two years but will probably last much longer. CALIPSO is nominally a three-year mission.