Solar flares cause GPS failures, possibly devastating for jets anddistress calls (Forwarded)

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Sept. 26, 2006

Solar flares cause GPS failures, possibly devastating for jets and
distress calls, Cornell researchers warn

By Thomas Oberst

Strong solar flares cause Global Positioning System (GPS) receivers to
fail, Cornell researchers have discovered. Because solar flares --
larger-than-normal radiation "burps" by the sun -- are generally
unpredictable, such failures could be devastating for "safety-of-life" GPS
operations -- such as navigating passenger jets, stabilizing floating oil
rigs and locating mobile phone distress calls.

"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.

Alessandro Cerruti, a graduate student working for Kintner, accidentally
discovered the effect on Sept. 7, 2005, while operating a GPS receiver at
Arecibo Observatory in Puerto Rico, one of six Cornell Scintillation
Monitor (SCINTMON) receivers. Cerruti was investigating irregularities in
the plasma of the Earth's ionosphere -- a phenomenon unrelated to solar
flares -- when the flare occurred, causing the receiver's signal to drop
significantly.

To be sure of the effect, Cerruti obtained data from other receivers
operated by the Federal Aviation Administration (FAA) and the Brazilian
Air Force. He found that all the receivers had suffered exactly the same
degradation at the exact time of the flare regardless of the manufacturer.
Furthermore, all receivers on the sunlit side of the Earth had been
affected.

Cerruti will report on the findings Sept. 28 at the Institute of
Navigation Meeting in Fort Worth, Texas, where he will receive the best
student paper prize. The full results of the discovery will be published
in a forthcoming issue of the journal Space Weather.

The flare consisted of two events about 40 minutes apart: The first lasted
70 seconds and caused a 40 percent signal drop; the second lasted 15
minutes and caused a 50 percent drop. But this flare was moderate and
short-lived; in 2011 and 2012, during the next solar maximum, flares are
expected to be 10 times as intense and last much longer, causing signal
drops of over 90 percent for several hours.

"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. 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. Unfortunately, the former requires additional compromises to
receiver design, and the latter requires a new satellite design that
neither exists nor is planned.

"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.

The team was initially confused as to why the flare had caused the signal
loss. Then Kintner recalled that solar flares are accompanied by solar
radio bursts. Because the bursts occur over the same frequency bands at
which GPS satellites transmit, receivers can become confused, leading to a
loss of signal.

Had the solar flare occurred during the night in Puerto Rico or had
Cerruti been operating SCINTMON only at night, he would not have made the
discovery.

"We normally do observations only in the tropics and only at night because
that's where and when the most intense ionospheric irregularities occur,"
said Kintner. However, since no one had done it before, Cerruti was
looking at "mid-latitudes" (between the tropics and the poles), where
weaker irregularities can occur both night and day. As a result, SCINTMON
detected the solar flare.

Other authors of the forthcoming paper include D.E. Gary and L.J.
Lanzerotti of the New Jersey Institute of Technology, E.R. de Paula of the
Instituto Nacional de Pesquisas Espaciais and Cornell research associate
Hien Vo.

[Thomas Oberst is a science writer intern at the Cornell Chronicle.]

IMAGE CAPTION:
[http://www.news.cornell.edu/stories/...lar_flares.jpg (113KB)]
Graduate student Alessandro Cerruti, left, and Professor Paul Kintner work
on the antenna on the roof of Phillips Hall. They have found that the
kinds of large solar flares expected in five years or so could produce
massive outages of all GPS receivers on the day side of the Earth.
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