E3 Engineering DivisionBrown Bag Series Lunch with Academia

February 15th, 2008

Coordinated by 4.1.M.1, the Electromagnetic Environmental Effects Engineering Division

Who: Cornell University Professor, Paul M. Kintner Jr.What: Presentation and Discussion of Space Weather Research and its

Impact upon Communication-Electronic EquipmentWhere: Wyle Laboratory, Lexington Park , MDWhen: Friday, Feb 15th 2008

Time: 0900-1200Why: Cooperative Between Academia and Acquisition Engineering

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

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

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.

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?

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

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

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 satellitesignal

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

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

GPS Frequency

C/N

o d

B-H

z

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/N

o d

B-H

z

C/N

o d

B-H

z

"Prediction is very difficult, especially if it's about the future." -- Niels Bohr, Danish Physicist, 1922 Nobel Prize Winner.

December 6, 2006X6 Solar Flare

GPSfrequencies

Start of solar flareand solar radio burst

Other Dec. 2006 Events

Dec 13

How Does Dec. 6, 2006 Event Fit into Historical Context?

Region of observations that we do notunderstand

Dec 6

Dec 14

3 yr 11 yr 30 yr

Solar Radio Bursts1960-2000

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)

Affected Civilian Systems

(at least 4 satellites from all stations)

No loss of Non-Precision Approach

(~1.5 minutes)

NASA DGPS SystemFAA WAAS Miami Receiver

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

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?

Change Space Weather Topic to Scintillations and Effects on GPS

Receivers

The Ionosphere introduces two problems for GPS

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).

mdF 4002

IPPi

F

VV

=19 cm d=350 km

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 F

• Begin after sunset and can persist throughout night

• Seasonal variations• More intense during solar

maximum

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

But Irregularities and Scintillations Can Occur Anywhere

Kyoto, Japan Ithaca, NY

(associated with geomagnetic storms)

Why Do Receivers Stop Tracking?Kalman Filter Tracking Loop

Variable PLL bandwidth

5 Hz PLL

15 Hz PLL

KFPLL and

CBPLL

KFPLL

CBPLL

Half-cycle Phase Jumps during Deep Fadessignals post processed after data wipe off

Canonical fade

Why Should Deep Fades Have Half Cycle Phase Jumps?

Direct Path Signal

DiffractedSignals

Resultant

DiffractedSignals

Direct Path Signal

Resultant

Before After

Weak Fade Deep Fade

Phasespace

Phasespace

Canonical fade in I-Q space

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.

Conclusion

• Design in a plan B

• Thank you