E3 Engineering Division

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E3 Engineering Division Brown Bag Series Lunch
with Academia February 15th, 2008
Who Cornell University Professor, Paul M.
Kintner Jr. What Presentation and Discussion of
Space Weather Research and its Impact upon
Communication-Electronic Equipment Where Wyle
Laboratory, Lexington Park , MD When Friday, Feb
15th 2008 Time 0900-1200 Why Cooperative
Between Academia and Acquisition Engineering
Coordinated by 4.1.M.1, the Electromagnetic
Environmental Effects Engineering Division
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Who Are We?

• GPS Laboratory gps.ece.cornell.edu
• ONR funding starting 1995
• Original purpose to diagnose scintillation
  effects on GPS receivers
• Needed to develop our own GPS receivers
• Highlights of group
• First fast GPS scintillation receiver (50 sps)
• First software receivers on Pentiums and DSP
  chips (L1 CA only and L1 CA/L2C)
• Sounding rocket GPS receivers
• Decoding of first Galileo PRN code (83,000 hits
  on web site)
• Numerous papers on the effects of scintillations
  on GPS receivers
• First measurements of solar radio burst impacts
  on GPS receivers

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Who Are We?

• Teaching program
• Introductory and Advanced courses in GPS
  receivers design
• Masters and PhD design programs
• Provided GPS receivers for satellites ICECube
  (cubesat) and CUSat (AF competition CDGPS)
• Software receivers
• Graduates at U of Illinois, VT, AFRL, MITRE,
  Novatel, Rockwell-Collins, Boeing
• Equipment
• Digital storage receivers, GPS Signal
  Simulators, and Field arrays
• Ithaca, Brazil, Hawaii, Puerto Rico, China

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Why Am I Here?

• To provide outreach concerning space weather
• To provide input for the committee Economic and
  Societal Impacts of Space Weather of the
  National Academy of Sciences, meeting this Spring.

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Overview of Space Weather and GPS

• Scintillations
• Amplitude
• Phase
• Overview when and where (climate)
• Canonical scintillations
• Cycle slips etc.

• Solar radio bursts
• Evidence for solar radio bursts affecting GPS
  receivers
• History of solar radio bursts
• Next solar maximum?

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Does this really matter?
The Standard Positioning Service (SPS) is a
positioning and timing service which will be
available to all GPS users on a continuous,
worldwide basis with no direct charge. SPS will
be provided on the GPS L1 frequency which
contains a coarse acquisition (C/A) code and a
navigation data message. SPS provides a
predictable positioning accuracy of 100 meters
(95 percent) horizontally and 156 meters (95
percent) vertically and time transfer accuracy to
UTC within 340 nanoseconds (95 percent). The
Precise Positioning Service (PPS) is a highly
accurate military positioning, velocity and
timing service which will be available on a
continuous, worldwide basis to users authorized
by the U.S. P(Y) code capable military user
equipment provides a predictable positioning
accuracy of at least 22 meters (95 percent)
horizontally and 27.7 meters vertically and time
transfer accuracy to UTC within 200 nanoseconds
(95 percent). PPS will be the data transmitted on
the GPS L1 and L2 frequencies. PPS was designed
primarily for U.S. military use. It will be
denied to unauthorized users by the use of
cryptography. PPS will be made available to U.S.
and military and U.S. Federal Government users.
Limited, non-Federal Government, civil use of
PPS, both domestic and foreign, will be
considered upon request and authorized on a
case-by-case basis, provided
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Solar Radio Bursts and Newly Discovered Effects
on GPS Receivers The Surprise on Dec 6, 2006
Number of L2/P signals tracked by civilian
receivers in IGS network
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How solar radio bursts affect GPS
receivers
Solar radio burst waves
GPS satellite signal

• Radio waves reach GPS receivers from both GPS
  satellites and the sun.
• The radio waves from sun appear as noise. They
  become more intense during a solar flare
• If the solar radio waves become too intense, then
  they dominate the signal from the satellite.
  That is the signal-to-noise ratio becomes
  smaller.
• If signal-to-noise ratio becomes too small, then
  the receiver can no longer track the GPS signal
  and loses all ranging information.

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Which GPS receivers are affected??

• All GPS receivers in sunlight are affected.
• All GPS satellites seen by a receiver are
  affected.
• Affects GPS receivers on the ground and in space
• As noise of cocktail
• party increases weak
• voices are drowned out

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First Quantitative Measurement of SRB Effects on
GPS signal
C/No dB-Hz
GPS Frequency

• Effect is small 2.7 dB
• Related to RHC power because GPS signal is RHC
• September 7, 2005

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When Details Are Worked Out Agreement Is
Convincing
C/No dB-Hz
C/No dB-Hz

• Demonstrates that SRB of 10,500 SFU RHC produces
  3 dB attenuation in signal
• Attenuation is independent of elevation

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"Prediction is very difficult, especially if it's
about the future." -- Niels Bohr, Danish
Physicist, 1922 Nobel Prize Winner.
December 6, 2006 X6 Solar Flare
GPS frequencies
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Other Dec. 2006 Events
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How Does Dec. 6, 2006 Event Fit into Historical
Context?
Dec 6
Dec 13
Region of observations that we do not understand
Dec 14
Solar Radio Bursts 1960-2000
3 yr
11 yr
30 yr
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Why we do not understand this region

• USAF Radio Solar Telescope Network provides the
  vast majority of historical data
• 2006 Dec 06
• 13,000 SFU RSTN Flux Density (1415 MHz)
• 1,000,000 SFU Owens Valley Solar Array (1400MHz)
• 2006 Dec 13
• 130,000 SFU RSTN Flux Density (1415 MHz)
• 440,000 Nobeyama Radio Observatory (1400MHz)
• 2006 Dec 14
• 2,700 SFU RSTN Flux Density (1415 MHz)
• 50,000 (OVSA 100,000 at 1.6 GHz)

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Affected Civilian Systems
No loss of Non-Precision Approach
(at least 4 satellites from all stations)
(1.5 minutes)
FAA WAAS Miami Receiver
NASA DGPS System
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Affected Military Systems?

• NOAA Memo to Brigadier General David L. Johnson,
  USAF (Ret.) Director, National Weather Service
• d. GPS From GPSOC at Schriever AFB 06 Dec At
  approximately 6 Dec/2000Z there was a widespread
  loss of GPS in the Mountain States region,
  specifically around the 4 corners region of
  NM/CO. Several aircraft reported losing lock on
  GPS and were tracking 7-9 satellites, and
  abruptly loss locks and were then tracking 0-1.
• Later denied in letter to GPS World

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Solar Radio Burst Conclusions

• Solar Radio Bursts can be much more intense than
  previously believed.
• Affect GPS receivers for 10-30 minutes
• All GPS satellite signals and WAAS signals are
  affected in sun lit hemisphere
• Truly uninterrupted GPS system operation is an
  extreme challenge
• Future research
• How were GPS receivers affected, why were some
  more robust than others?
• Why does historical record appear to be
  inaccurate or was Dec 2006 truly anomalous,
  GPS-SRB forensics?

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Change Space Weather Topic to Scintillations and
Effects on GPS Receivers
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The Ionosphere introduces two problems
for GPS
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Scintillations

• Amplitude decreases (fades) and increases
• Spatial scale determined by Fresnel length
• Temporal scale determined by
• Amplitude determined by ionospheric electron
  density, depth of irregularities, and frequency
  of signal (L2 worse than L1).

l19 cm d350 km
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Where and When?

• Most common scintillations are associated with
  bands around the magnetic equator called the
  equatorial anomalies
• Associated with the bands are Raleigh-Taylor
  instabilities which produce electron density
  irregularities at lF
• Begin after sunset and can persist throughout
  night
• Seasonal variations
• More intense during solar maximum

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Distribution Over Brazil

• S4std(ampl)/
• GPS satellites tracked by a few GPS receivers in
  Brazil
• S4 0.8 will cause loss of signal tracking

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But Irregularities and Scintillations Can Occur
Anywhere
Kyoto, Japan
Ithaca, NY
(associated with geomagnetic storms)
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Why Do Receivers Stop Tracking?Kalman Filter
Tracking LoopVariable PLL bandwidth
KFPLL
5 Hz PLL
KFPLL and CBPLL
CBPLL
15 Hz PLL
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Half-cycle Phase Jumps during Deep Fadessignals
post processed after data wipe off
Canonical fade
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Why Should Deep Fades Have Half Cycle Phase Jumps?
Weak Fade
Deep Fade
Diffracted Signals
Phase space
Phase space
Diffracted Signals
Direct Path Signal
Direct Path Signal
Resultant
Resultant
Before
After
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Canonical fade in I-Q space
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Lessons To Take Home

• If you need only 95 availability, dont worry
  about space weather.
• If you need truly continuous 100 availability,
  learn about space weather
• If operation in the tropics is important,
  scintillations will be a frequent problem.
• Scintillations can occur anywhere although they
  are less likely outside the tropics.
• Large amplitude solar radio bursts are infrequent
  but they affect the entire dayside of the Earth.
• We do not know how infrequent so stay alert
  during the next solar maximum.

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Conclusion

• Design in a plan B
• Thank you