Solar flares 'may threaten GPS'

a.. April 5, 2007 - 6:54AM

Powerful radio bursts from the sun may threaten the Global Positioning
System (GPS), American scientists say.
The technology is increasingly vital for activities including navigating
cars and airplanes, bank financial transfers and more.

"Our increasingly technologically dependent society is becoming increasingly
vulnerable to space weather," David L Johnson, director of the US National
Weather Service, said at a briefing.

GPS receivers have become widely used in recent years, using satellite
signals to navigate airplanes, ships and automobiles, and in the use of
mobile phones, mining, surveying and many commercial applications.

Indeed, banks use the system to synchronise money transfers, "so space
weather can affect all of us, right down to our wallet," said Anthea J
Coster, an atmospheric scientist at the Haystack Observatory of the
Massachusetts Institute of Technology.

The cause for their concern, Johnson said, was an unexpected solar radio
burst on December 6 that affected virtually every GPS receiver on the
lighted half of Earth.

Some receivers had a reduction in accuracy while others lost the ability to
determine position, he said.

Solar activity rises and falls in 11-year cycles with the next peak expected
in 2011.

If that increasing level of activity produces more such radio bursts the GPS
system could be seriously affected, the researchers said.

And protecting the system is no simple task, added Paul M Kintner Jr, a
professor of electrical engineering at Cornell University, who monitored the
December event.

There are two possible ways to shield the system, he said, both very
expensive. Either alter all GPS antennas to screen out solar signals or
replace all the GPS satellites with ones that broadcast a stronger signal.

That is why it is essential to learn more about the sun's behaviour quickly
in an effort to find ways to predict such events, the researchers said.

In addition to the GPS system, the December solar flare affected satellites
and induced unexpected currents in the electrical grid, Johnson said.

"The effects were more profound than we expected and more widespread than we
expected," added Kintner.

Dale E Gary, chairman of the physics department of the New Jersey Institute
of Technology, said the burst produced 10 times more radio noise than any
burst previously recorded.

The difference between that burst and normal solar radio emissions "was like
the difference between the noise level of a normal conversation and the
noise level in the front row of a rock concert," he said.

"This is a wake-up call" to improve technology, commented Anthony J
Mannucci, group supervisor at NASA's Jet Propulsion Laboratory.

Patricia H Doherty, co-director of the Institute for Scientific Research at
Boston College, said the burst affected but did not shut down the Federal
Aviation Administration's Wide Area Augmentation System, which uses GPS
signals to help in navigation.

Most WAAS ground stations maintained contact with enough satellites to
continue working, although their accuracy was somewhat affected, she said.

The stations have to maintain contact with at least four satellites to work,
but they usually monitor at least 10 to increase their accuracy, she said.
Most were able to meet the minimum, she said.

The briefing came at a Space Weather Enterprise Forum convened by the
National Oceanic and Atmospheric Administration to discuss the effects of
solar activity. Because of its increasing importance, Johnson said, the
Weather Service's Space Environment Centre was converted from a mainly
research centre in 2005 to an operational centre reporting on solar activity
and its impacts.



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