Abstract from ION GNSS 2006 (Sept. 26-29)
Observed GPS and WAAS Signal-to-Noise Degradation Due to Solar Radio Bursts
A. Cerruti, Cornell University
GPS signals, systems, and navigation accuracy are vulnerable to a
variety of space weather effects that are caused mostly by the
ionosphere. However, the sun, which is sometimes a strong radio source,
is the cause of GPS signal interference presented here. The first
direct observations of GPS L1 (1.57542 GHz) signal-to-noise ratio
degradation on two different models of GPS receivers due to the solar
radio burst associated with the 7 September 2005 solar flare are
presented.
Signal-to-noise ratio data from three identical, collocated receivers
at Arecibo Observatory and also from four identical receivers of a
different model located in Brazil, were available at the time of the
solar radio burst. These receivers were all in the sun-lit hemisphere
and all were affected similarly. The maximum solar radio burst power
associated with the 7 September 2005 flare had a peak intensity of
about 8,700 solar flux units (1 SFU = 10-22 W/m2-Hz) RHCP at 1,600 MHz,
which caused a corresponding decrease in the signal-to-noise ratio of
about 2.3 dB across all visible satellites. Only the right-hand,
circularly polarized (RHCP) emissions affected the GPS signals.
To confirm the effect, the solar radio burst associated with the 28
October 2003 flare was investigated. Although polarization data were
not available for this event, the maximum degradation at GPS L1 was
about 3.0 dB, and a degradation of 10 dB was observed on the
semi-codeless L2 signal for a solar radio burst of 13,600 SFU.
The event analyzed herein can be used to scale historical solar radio
bursts of 80,000 SFU. Decreases of 12 dB (21 dB) in the L1 (L2,
semi-codeless) signal-to-noise ratio are implied along with loss of
tracking for inadequately designed GPS receivers. Since solar radio
bursts affect all satellites in view of a receiver, all receivers in
the sun-lit hemisphere, the new Galileo navigation system, and all
space-based augmentation systems such as WAAS and EGNOS, they are a
potential threat to life-critical systems.
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