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E3 Engineering Division Brown Bag Series Lunch with Academia February 15 th , 2008

E3 Engineering Division Brown Bag Series Lunch with Academia February 15 th , 2008. Who: Cornell University Professor, Paul M. Kintner Jr. What: Presentation and Discussion of Space Weather Research and its Impact upon Communication-Electronic Equipment

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E3 Engineering Division Brown Bag Series Lunch with Academia February 15 th , 2008

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  1. 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

  2. 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

  3. 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

  4. 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.

  5. 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? Overview of Space Weather and GPS

  6. 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

  7. 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

  8. How solar radio bursts affect GPS receivers • 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. Solar radio burst waves GPS satellite signal

  9. 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

  10. First Quantitative Measurement of SRB Effects on GPS signal • Effect is small… 2.7 dB • Related to RHC power because GPS signal is RHC • September 7, 2005 C/No dB-Hz GPS Frequency

  11. When Details Are Worked Out Agreement Is Convincing • Demonstrates that SRB of 10,500 SFU RHC produces 3 dB attenuation in signal • Attenuation is independent of elevation C/No dB-Hz C/No dB-Hz

  12. Start of solar flare and solar radio burst "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

  13. Other Dec. 2006 Events

  14. 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 11 yr 30 yr 3 yr

  15. 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)

  16. 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

  17. 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

  18. 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?

  19. Change Space Weather Topic to Scintillations and Effects on GPS Receivers

  20. The Ionosphere introduces two problems for GPS

  21. 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). Scintillations l=19 cm d=350 km

  22. 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

  23. Distribution Over Brazil • S4=std(ampl)/<ampl> • GPS satellites tracked by a few GPS receivers in Brazil • S4 ≈> 0.8 will cause loss of signal tracking

  24. But Irregularities and Scintillations Can Occur Anywhere Kyoto, Japan Ithaca, NY (associated with geomagnetic storms)

  25. Why Do Receivers Stop Tracking?Kalman Filter Tracking LoopVariable PLL bandwidth KFPLL 5 Hz PLL KFPLL and CBPLL CBPLL 15 Hz PLL

  26. Half-cycle Phase Jumps during Deep Fadessignals post processed after data wipe off Canonical fade

  27. 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

  28. Canonical fade in I-Q space

  29. Lessons To Take Home • If you need only 95% availability, don’t 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.

  30. Conclusion • Design in a plan B • Thank you

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