Radar System Aboard NASA DC-8 Aims To Unveil The Mysteries Of Cloud Structures

During the current flights over the southern United States, NASA'sAirborne Cloud Radar is looking at clouds in an attempt to betterunderstand how clouds warm or cool Earth's atmosphere and how the presenceof clouds influences the world's climate.

"Clouds represent a scientific puzzle that researchers have been tryingto piece together for centuries," said Dr. Fuk Li, the principalinvestigator for the cloud radar at NASA's Jet Propulsion Laboratory,Pasadena, CA. "Scientists still don't know very much about the internal,vertical structures of clouds, and that leads to uncertainties in weatherand climate predictions. Using the cloud radar, we will be able to studyclouds in a new way that will help us understand their structure like neverbefore. Once we have the cloud vertical structure information, atmosphericscientists will have a much better handle on long-term predictions ofweather and climate change."

The cloud radar experiment was installed last month looking downward inthe tail area of the DC-8, based at NASA's Dryden Flight Research Center,Edwards, CA. The DC-8 then flew to Tinker Air Force Base near OklahomaCity, OK, the origination point of this series of missions in which theradar collects cloud data while the plane flies above the clouds.

Scientists will compare these data with measurements taken by satelliteand ground-based sensors, including the Department of Energy's SouthernGreat Plains Cloud and Radiation Testbed, a series of instruments spreadacross north central Oklahoma and south central Kansas.

The radar, taking vertical measurements of the clouds from above,operates at 94 gigahertz, making it sensitive to cloud particles. Theinstrument transmits radar energy, which bounces off the cloud particlesand is reflected back towards the aircraft. The radar measurements will becombined with information provided by other sensors to help analyze theproperties of the clouds observed.

This experiment has flown twice before aboard the DC-8 while stillunder development. The DC-8's unique features make it an ideal platformfor examining cloud structures, according to DC-8 mission manager ChrisJennison of Dryden.

"The DC-8 was selected because it is the only aircraft that is capableof this mission in terms of altitude, speed, range and capacity forcarrying scientists onboard. Since scientists can fly on the aircraft,they can operate their experiments themselves," Jennison said.

This Airborne Cloud Radar flight series is expected to total 20 flighthours. The experiment is designed to test several hypotheses andtechniques related to satellite remote sensing of extensive, long-lasting,non-precipitating layers of cloud in the middle and upper troposphere --atmosphere up to about 11 kilometers (seven miles) from Earth's surface.

It is expected that this instrument will be used in upcoming fieldexperiments to better understand cloud-climate processes. One such plannedexperiment is the Tropical Cirrus Experiment called CRYSTAL planned for2001. Eventually this instrument will be flown on satellite platformsdesigned to observe Earth's climate processes from space.

The Jet Propulsion Laboratory, a division of the California Instituteof Technology, developed the Airborne Cloud Radar in conjunction with theUniversity of Massachusetts, Amherst; Colorado State University, Ft.Collins; and Pennsylvania State University, Philadelphia.

The Airborne Cloud Radar is part of NASA's Earth Science enterprise, along-term research program designed to study Earth's land, oceans,atmosphere, ice and life as a total integrated system.