May 5, 1999
NASA Ames Research Center, Moffett Field, CA
NASA Dryden Flight Research Center, Edwards, CA
Sandia National Laboratories, Livermore, CA
General Atomics Aeronautical Systems, Inc., San Diego, CA
Pacific Missile Range Facility, Kauai Island, HA
NASA USING ROBOTIC AIRCRAFT TO STUDY SUBTROPIC CLIMATE
Properties of high-level cirrus clouds that may affect global warming were measured over the subtropical Pacific for the first time last week. Data were gathered using specially designed instruments carried by a remotely piloted aircraft flying at 50,000 feet altitude off the Hawaiian island of Kaua'i.
The measurements are being compiled to develop a global picture of how solar energy enters the atmosphere and moves within and through clouds. Clouds are effective at both reflecting incoming solar energy back to space, and absorbing longwave radiation from the Earth's surface. One of the key uncertainties of global climate models used to predict climate change is how these dual roles of clouds in reflecting and absorbing solar energy work. Data from the study will help scientists better understand these roles, and build more accurate global climate models.
"We measure solar energy that is transmitted and reflected by cirrus clouds, and this helps us understand the effect these clouds have on climate," said Dr. Peter Pilewskie, a principal investigator at NASA's Ames Research Center, Moffett Field, CA. "The clouds redistribute the solar energy received by Earth from the Sun; they also emit and absorb radiant energy at longer wavelengths. Some of the light is scattered back into space, some is transmitted down to the lower atmosphere and some is absorbed by the cloud."
The climate studies are being guided by Sandia National Laboratories for the Department of Energy's Atmospheric Radiation Measurement--Unmanned Aerospace Vehicle program. The Altus" aircraft being used as an aerial platform for the instruments was built by General Atomics Aeronautical Systems, Inc. for the National Aeronautics and Space Administration. NASA's Dryden Flight Research Center, Edwards, CA, provided the aircraft and is funding the flight series at the U.S. Navy's Pacific Missile Range Facility under NASA's Environmental Research Aircraft and Sensor Technology (ERAST) program.
The Altus has a two-stage turbocharged engine capable of taking the aircraft to 65,000 feet, above the tropopause where most clouds form. The flights began April 28, and the aircraft carries a 340-lb. payload of radiometers, laser-based lidar detection devices and similar instruments to collect and transmit information about clouds such as their optical properties and the size and concentration of particles they contain. A second aircraft, a DHC-6 Twin Otter, flies beneath the clouds in stacked formation with the Altus above, carrying radar from NASA that probes the ice and water content of the clouds.
"Last week's flights were the first of six to eight flights we plan to conduct through May 19," said Dr. Will R. Bolton of Sandia's Livermore, CA, laboratory, who is responsible for engineering aspects of the overall technical program. "The flights are both a scientific mission and a demonstration of the capability of using a remotely-operated aircraft in a sub-tropical environment." The remaining flights will be carried out under a variety of conditions, with the uninhabited Altus controlled by pilots on the ground.
"This experiment is a milestone in demonstrating the utility of robotic aircraft to do significant science missions," said Steve Wegener, the ERAST program's science and sensors manager at Ames.
NASA's Dr. James Stewart, manager of the ERAST program at Dryden that produced the Altus and other high-flying, long-duration uninhabited aircraft for environmental research, said the current series of flights by the Altus demonstrate the scientific and commercial potential of the remotely operated aircraft NASA is developing.
"This was the first time scientists have been able to get measurements from cirrus clouds with these instruments," he said. "All of the instruments and the aircraft worked very well, and the scientists were extremely pleased with the data they obtained from above the cirrus clouds. These were probably the most successful flights that Sandia has flown while recording good atmospheric radiation data at these altitudes."
Roughly 25 researchers from three Department of Energy laboratories, a dozen universities, three NASA centers and four private companies are working together at the Navy facility during the four-week mission.
In the future, these climate researchers would like to conduct similar measurements in a deep tropical region, closer to the equator, where tropical storms are responsible for bringing much moisture from the ocean into the atmosphere in a process that drives the dynamics of weather patterns far and wide.
The scientists' long range goal is to develop enough information to improve the accuracy of predictive models of climate change. Once the dynamics are better understood, the climate models can reflect that understanding and improve forecasting.
Other key participants in the study include: the University of California, San Diego Scripps Institute of Oceanography and Colorado State University, which are providing radiometric instruments; Sandia, Los Alamos and Lawrence Livermore National Laboratories, which are developing instrumentation for these small, light aircraft; the University of Maryland, which provides the mission scientist; and Pacific Northwest National Laboratory, which provides data management.
Sandia is a multiprogram Department of Energy laboratory, operated by a subsidiary of Lockheed Martin Corp. With main facilities in Albuquerque, NM., and Livermore, CA, Sandia has major research and development responsibilities in national security, energy, and environmental technologies. The Dryden Flight Research Center is NASA's Center of Excellence for atmospheric flight research. The Navy's Pacific Missile Range Facility at Barking Sands, Kaua'i, Hawaii, is the world's largest instrumented, multi-environment test range for encroachment-free military testing and fleet tactical training objectives as well as civilian scientific missions. General Atomics Aeronautical Systems, Inc., based in San Diego, CA, is a leading manufacturer of uninhabited aircraft surveillance systems. The Altus is a larger, high-altitude civilian variant of its Gnat` and Predator" aircraft built for the U.S. military.
More information for the experiment is available on the Internet at: http://armuav.atmos.colostate.edu/uavs99/uavs99.html
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