Global Positioning System at Solar Flare Mercy

Global Positioning System at Solar Flare Mercy



   
April 2007 - Strong solar flares can 
cause Global Positioning System, GPS, receivers on Earth to 
fail, Cornell researchers have discovered. They predict that 
the large solar flares expected in five years could produce 
outages of all GPS receivers on the day side of Earth with 
devastating consequences for aviation and maritime operations, 
disaster relief, and telecommunications. 
The findings were announced Thursday in Washington, DC, at the 
first Space Weather Enterprise Forum, a gathering of academic, 
government and private sector scientists who study the Earth's 
vulnerability to the impacts of space weather. 
"If you're driving to the beach using your car's navigation 
system, you'll be OK. If you're on a commercial airplane in 
zero visibility weather, maybe not," said Paul Kintner Jr., 
professor of electrical and computer engineering at Cornell 
and head of Cornell's GPS Laboratory. 
The Global GPS Network is a set of precise GPS receivers used 
for scientific and real-time applications including a 
positioning service that can provide a user's position with 10 
to 20 centimeter accuracy anywhere in the world, on land, in 
the air or in Earth's orbit. 
Solar flares are accompanied by solar radio bursts. Because 
the bursts occur over the same frequency bands at which GPS 
satellites transmit, the radio waves act as noise, leading to 
a loss of signal. 
Alessandro Cerruti, a graduate student working with Kintner, 
accidentally discovered the effect on September 7, 2005, while 
operating a Cornel GPS receiver at Arecibo Observatory in 
Puerto Rico. Cerruti was investigating a phenomenon unrelated 
to solar flares when a flare occurred, causing the receiver's 
signal to drop significantly. 
A close-up of the September 7, 2005 solar flare taken with 
NASA's Transition Region and Coronal Explorer spacecraft. To be
 sure of the effect, Cerruti obtained data from receivers 
operated by the Federal Aviation Administration, FAA, and the 
Brazilian Air Force, among others. He found that all receivers 
on the sunlit side of the Earth had been affected. 
Kintner and Cerruti confirmed the effect on December 6, 2006, 
when a huge solar flare created an unprecedented intense solar 
radio burst causing large numbers of receivers to stop 
tracking the GPS signal. 
"In December, we found the effect on GPS receivers were more 
profound and wide spread than we expected," said Kintner. "Now 
we are concerned more severe consequences will occur during 
the next solar maximum." 
The next solar maximum, the highest point of the Sun's 11 year 
activity cycle, is due in 2011. The most recent solar minimum 
occurred in 2006, but even during minimums the Sun can emit 
giant flares and radio bursts. 
Sunspot counts and solar X-ray flares during the last three 
solar cycles. Solar activity continues even during solar 
minimums. (Graph courtesy David Hathaway, NASA/NSSTC)
"This solar radio burst occurred during the solar minimum, yet 
produced as much as 10 times more radio noise than the 
previous record," said Dale Gary, Ph.D., chair and professor 
of the physics department at New Jersey Institute of 
Technology, NJIT. 
"Measurements with NJIT's solar radiotelescope confirmed, at 
its peak, the burst produced 20,000 times more radio emission 
than the entire rest of the Sun. This was enough to swamp GPS 
receivers over the entire sunlit side of Earth," he said. 
"Soon the FAA will require that every plane have a GPS 
receiver transmitting its position to air traffic controllers 
on the ground," warned Cerruti. "But suppose one day you are 
on an aircraft and a solar radio burst occurs. There's an 
outage, and the GPS receiver cannot produce a location." 
"It's a nightmare situation," Cerruti said. "But now that we 
know the burst's severity, we might be able to mitigate the 
problem." 
The only solutions, suggested Kintner, are to equip receivers 
with weak signal-tracking algorithms or to increase the signal 
power from the satellites. But the first idea requires 
compromises to receiver design, and the other suggestion 
requires a new satellite design that neither exists nor is 
planned. 
Alessandro Cerruti, left, and Professor Paul Kintner work on 
the antenna on the roof of Cornell's Phillips Hall. 
"I think the best remedy is to be aware of the problem and 
operate GPS systems with the knowledge that they may fail 
during a solar flare," Kintner said. 
At the National Aeronautics and Space Administration, NASA, 
the Global Positioning System provides key positioning, 
navigation and timing capabilities onboard the Space Shuttle, 
the International Space Station, and on numerous science 
satellites. 
NASA Administrator Michael Griffin says GPS "is a national 
asset that will be used to further America's long-term space 
exploration objectives under the Vision for Space 
Exploration." 
Looking into the future, Griffin said, "GPS precision time 
signals may become the electronic foundation for the 
communication and navigation systems of human and robotic 
explorers and enable an "interplanetary Internet" for the 
global community to use." 
On Earth, GPS signals support entire industries such as 
aviation, maritime, disaster relief, surveying, banking, and 
telecommunications. 
"NASA wants to better understand this solar phenomenon so we 
can limit the adverse impacts on real-time systems," said Tony 
Mannucci, Ph.D., principal technical staff and supervisor, 
Ionospheric and Atmospheric Remote Senvironment newsing Group at the NASA 
Jet Propulsion Laboratory. 
There are three important points to remember about solar radio 
bursts, said Anthea Coster, Ph.D., of the Massachusetts 
Institute of Technology's Haystack Observatory. 
"First, society cannot become overly reliant on technology 
without an awareness and understanding of the effects of 
future space weather disruptions." 
"Second," she said, "the December 6 event dramatically shows 
the effect of solar radio bursts is global and instantaneous."
 "Third, and equally important, the size and timing of this 
burst were completely unexpected and the largest ever 
detected," said Coster. "We do not know how often we can 
expect solar radio bursts of this size or even larger." 

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