On today's digital battlefield, where AA batteries are almost as critical as bullets, researchers are looking for ways to forecast "weather" conditions hundreds of miles up where satellites orbit. Over the past decade, scientists have focused much of their effort on forecasting the effects of large outbursts from the sun, which can fry satellite circuits and trigger surges in earthbound utility transmission lines.
Now, military and civilian researchers are paying increased attention to turbulence in Earth's ionosphere, which can weaken navigation, intelligence, and other signals until they vanish under useless noise. While solar storms can aggravate these effects, they can appear almost daily with or without a major solar eruption.
In Iraq, "all of our operations are very finely tuned" to minimize civilian casualties, notes US Air Force Capt. Kelly Doser, currently working at the National Oceanic and Atmospheric Administration's Space Environment Center in Boulder, Colo. Because today's weapons that rely on navigation satellites for guidance, "any little thing that creeps in could have a very heavy impact on how the mission is done."
By many accounts, the US-led conflict is more reliant on digital information than any in history. Encrypted voice communications, digital images of bomb and missile damage from remotely piloted aircraft and precision munitions, as well as search-and-rescue operations, all depend on satellites. Since the Gulf War in 1991, the military's demand for satellite services has grown tenfold, prompting the Pentagon to contract with commercial-satellite operators for the capacity it needs.
Meanwhile, the military's global-positioning satellite (GPS) network has become its backbone for navigation and the key technology behind a new generation of precision-guided weapons.
One potential source of error lies in the ionized portion of Earth's atmosphere, which begins about 30 miles up and through which GPS signals must pass, researchers say. Just as turbulence in the lower part of the atmosphere can give starlight its twinkle, turbulence in the ionosphere can cause GPS satellite signals to strengthen and fade - sometimes to the point where receivers lose the signals completely.
"The problem usually occurs after sundown and doesn't clear up until after midnight," says Joseph Kunches, chief of space operations at the Space Environment Center.
At sundown the lower ionosphere grows less dense than the overlying layers, triggering "bubbles" that rise and generate turbulences that move through the surrounding ionosphere. The US Air Force has established a global network of 12 ground-based sensors, which can detect the effect. One is located in the Gulf region. Each day, the Pentagon's Central Command gets a briefing on conditions the network observes, notes David Anderson, a research associate with the University of Colorado's Cooperative Institute for Research in Environmental Sciences.
Dr. Anderson notes that the US Air Force Research Laboratory has developed a computer system that allows users to identify other satellites on orbit whose signal paths aren't affected, so that an operator can switch communications to a different satellite. But experts lack a means of forecasting these effects well in advance.
One of the critical needs, researchers say, is more sensors on orbit to monitor changes in the ionosphere. Later this year, the Air Force is scheduled to launch a satellite dedicated to scintillation forecasting.
In addition, the US and Taiwan are scheduled to launch a constellation of six microsatellites in 2005 that will gather more than 3,000 measurements a day of GPS signals as they pass through the atmosphere from various angles. Researchers say the measurements, which also will be used for weather and climate monitoring, will aid in forecasting the phenomenon and will be important for their understanding of ionospheric scintillation.