The Evolution of GPS Ionosphere Scintillation Monitoring Over the Last 25 Years

Transcription

1 The Evolution of GPS Ionosphere Scintillation Monitoring Over the Last 25 Years Dr. A.J. Van Dierendonck, AJ Systems May 2014 CSNC ION Panel 1

2 36-40 Years Ago 1978 to 1982! Even before GPS, satellite signals were used to measure ionosphere scintillation! Documented in 1978 Radio Science paper Early Results From the DNA Wideband Satellite Experiment -- Complex-Signal Scintillation, Fremouw, et. al., Volume 13, Number 1, pages , January- February 1978.! Space Vehicle was a modified Navy Navigation Satellite (Transit) with payload replaced with one that broadcast 10 CW signals at frequencies between VHF and S-Band! Called DNA Wideband Satellite Experiment! Early measurements on Transit signals (150 and 400 MHz) May 2014 CSNC ION Panel 2

3 DNA Wideband Satellite Experiment! This experiment was the basis for monitoring using GPS in more recent years! Conducted by Stanford Research Institute (SRI) now SRI International! 1000 km near-polar orbit Phased so signals passed through the ionosphere in critical locations at critical times (not on purpose)! Receivers measured carrier power and phase of the 10 CW signals simultaneously! Power measurements were a result of receiver AGC! Signal processing described in paper is the basis for later processing of GPS signals for scintillation monitoring But somewhat different for a number of reasons to follow May 2014 CSNC ION Panel 3

4 Why GPS and DNA Processing is Different! GPS Doppler is much lower! This makes detrending more difficult Detrending is the method of discriminating against normal systematic effects with similar frequency content Such as multipath fading and oscillator effects! GPS multipath fades are longer because of the lower Doppler! Basic algorithms are similar, but frequency cutoffs are different May 2014 CSNC ION Panel 4

5 33-35 Years Ago 1979 to 1981! Early Use of GPS to Measure Ionosphere Scintillation and TEC using Expensive Equipment (GPS Receivers)! SRI International under contract to AFRL! Rack-mounted Stanford Telecom 5010 Receiver L1 and L2 AGC used for amplitude measurements Post Correlation TEC measured using L1 and L2 code epoch measurements using HP Time Interval Counters! Measurement Campaigns at Ascension Island and at Kwajalein, Marshall Islands May 2014 CSNC ION Panel 5

6 25 Years Ago ! Transionospheric Sensing System (TISS)! US Air Force Procurement Attempt using more modernized GPS receivers (relative to 5010) Baseline using GPS Monitor Station receivers Rack mounted Analog Receivers Quite Expensive Capable of tracking encrypted P-code signals! Program was cancelled because of high expense! Yours truly was involved! So was Jack Klobuchar (then with AFRL)! High expense was not our fault May 2014 CSNC ION Panel 6

7 Early Commercial GPS Scintillation Monitors May 2014 CSNC ION Panel 7

8 16-22 Years Ago ! Development of commercial Scintillation Monitor! PAQ Communications received Small Business Innovative Research (SBIR) contract from AFRL to study and test a software-modified L1 C/A code receiver to extract scintillation parameters on the L1 signal (Phase I) AJ Systems was a sub-contractor later starting a Partnership with PAQ Communications called GPS Silicon Valley! This was followed by a Phase II effort to design and test a low-cost portable Ionospheric Scintillation Monitor (ISM) First Commercial Version was an early NovAtel GPStation with an internal AT-Cut Oven-Controlled Crystal Oscillator (OCXO) as a phase reference May 2014 CSNC ION Panel 8

9 16-22 Years Ago (Continued)! Phase Measurement Problems! This OCXO exhibited frequency popping, that occasionally masked phase scintillation effects Problem was caused by the fact the AT-Cut OCXO was tuned to a higher frequency ( MHz) See a IEEE Frequency Control Symposium paper published in 1998! Problem was solved by phase locking the receiver reference to a lower-frequency low-phase-noise OCXO An extra auxiliary card was required to house this OCXO and Phase-Lock-Loop May 2014 CSNC ION Panel 9

10 Early Version Scintillation Monitor With Internal AT-Cut OCXO May 2014 CSNC ION Panel 10

11 AT-CUT OCXO FREQUENCY POPPING EFFECT 0.8 RMS DETRENDED PHASE - RADIANS PH 1 PH 3 PH 10 PH 3O PH TIME - SECONDS May 2014 CNSC ION Panel 11

12 GSV4000 Single Frequency (L1) ISM First truly commercial version used a NovAtel 3951 PC Card, plus a GSV3003A PC frequency conversion card with 10 MHz SC-cut OCXO May 2014 CSNC ION Panel 12

13 GSV4001 Single Frequency (L1) ISM May 2014 CSNC ION Panel 13

14 GSV4004 Series GSV4004, 4004A and 4004B Over 300 Sold Low Phase Noise SC-Cut OCXO included in the Enclosure May 2014 CSNC ION Panel 14

15 GSV4004 Series of Scintillation Monitors GSV4004/GSV4004A GSV4004B GSV4004/GSV4004A Rear Panel GPS702 L1/L2 Antenna May 2014 CSNC ION Panel 15

16 GSV4004B Scintillation & TEC Monitor First Dual Frequency Monitor with dual frequency antenna Measures TEC and all scintillation parameters on L1 Including Scintillation parameters from up to 3 SBAS GEOs May 2014 CSNC ION Panel 16

17 Firmware Upgraded to Measure Scintillation in path to SBAS GEO! As opposed to GPS SVs, cannot measure coherent phase and amplitude over 20 msec (50 Hz rate)! Symbol rate is 500 baud! Instead, measure decision-directed phase and amplitude at 50 Hz rate! Somewhat more prone to cycle-slips But S4 can be measured non-coherently (phase cannot be)! Phase measurements are also corrupted by SBAS Ground Uplink Station phase control May 2014 CSNC 2014 ION Panel 17

18 Statistics of Measured S4 From a Geostationary Satellite Average + 1-Sigma S4 mod GISM Corrected S GPS Time of Day May 2014 CSNC 2014 ION Panel 18

19 GPStationG6 The Newest Evolved from GSV4004B Includes Scintillation and TEC Measurements on GPS L2C and L5 Includes L1/L2 on GLONASS Firmware Upgrade Path to Galileo and Beidou May 2014 CSNC ION Panel 19