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Research ArticleRegular Papers
Open Access

WAAS and the Ionosphere – A Historical Perspective: Monitoring Storms

Lawrence Sparks, Eric Altshuler, Nitin Pandya, Juan Blanch, and Todd Walter
NAVIGATION: Journal of the Institute of Navigation March 2022, 69 (1) navi.503; DOI: https://doi.org/10.33012/navi.503
Lawrence Sparks
1Jet Propulsion Laboratory, California Institute of Technology
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  • For correspondence: [email protected]
Eric Altshuler
2Sequoia Research Corporation
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Nitin Pandya
3Raytheon Technologies Corporation
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Juan Blanch,
4Stanford University
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Todd Walter
4Stanford University
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  • FIGURE 1
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    FIGURE 1

    WAAS receiver sites in North America since March of 2008

  • FIGURE 2
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    FIGURE 2

    Process flow diagram showing how WAAS monitors ionospheric disturbances: a) measurements are recorded at WAAS reference stations (WRSs); b) measurements are converted to estimates of vertical delay; c) an ionospheric grid delay (IGD) is computed for each ionospheric grid point (IGP); d) the irregularity metric is evaluated at each IGP; e) the ionospheric perturbation metric (IPM) for the entire coverage region is evaluated; f) if the Moderate Storm Detector has not tripped, the grid ionospheric vertical error (GIVE) at each IGP is evaluated using the quiet-time branch of the ionospheric threat model; g) otherwise, if the Extreme Storm Detector has not tripped, the GIVE at each IGP is evaluated using the disturbed-time branch of the ionospheric threat model; h) otherwise, each GIVE is set to its maximum possible value GIVEmax; and i) the IGDs and GIVEs are broadcast to WAAS users.

  • FIGURE 3
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    FIGURE 3

    WAAS IGP masks and pierce point filter lines (PPFL): (a) IOC (July 10, 2003, WAAS IGP mask 002, no PPFL); (b) LPV Release 6/7 (September 27, 2007, WAAS IGP mask 003, PPFL in brown); (c) LPV Release 8/9.2 (September 22, 2008, WAAS IGP mask 004, PPFL in blue); for WFO Release 3A (October 20, 2011), the IGP enclosed by the red square was added (WAAS IGP mask 005), and the PPFL was extended 20˚ eastward; (d) WFO Release 3A1 (January 20, 2012, WAAS IGP mask 006, PPFL in amber). Note: WAAS IGP mask 007 for Release 51-CY18 (September 11-14, 2018) is identical to mask 006 in terms of IGP locations, but GIVE floor values at [15˚N 100˚W] and [15˚N 105˚W] change from 15 m to 3 m. Black squares identify IGPs near Hawaii where, due to the isolation of the WRS in Honolulu from other WAAS WRSs, GIVEs are always set to “not monitored.”

  • FIGURE 4
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    FIGURE 4

    The distribution of IPPs for equivalent vertical delays observed at 20:57:30 UTC on June 1, 2013. The black dashed line encloses the IPPs included in the fit centered on the IGP at [35˚N, 125˚W] identified by the x. The red arrow points from the IGP to the centroid of the IPPs included in the fit. The fit domain radius Rfit is 1,589 km and the relative centroid metric (i.e., the length Rcentroid of the centroid vector divided by the fit radius Rfit) is 0.58. Magenta open circles indicate the positions of GPS satellites projected onto the ionospheric shell. Open brown squares identify receiver locations.

  • FIGURE 5
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    FIGURE 5

    Median value of 100 largest absolute vertical delay residuals for 16 storms in solar cycle 24, no data deprivation. Brown lines are contours of constant geomagnetic latitude.

  • FIGURE 6
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    FIGURE 6

    The value of the irregularity metric of each IGP at 23:00 UTC for (a) a weak storm on July 26, 2004; (b) a moderate storm on October 24, 2011; and (c) an extreme storm on April 6, 2000. The peak value is indicated by the magenta rectangle in each plot.

  • FIGURE 7
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    FIGURE 7

    The magnitude of the Dst index (nT) from October 27, 2003 through November 2, 2003. [Available at: World Data Center for Geomagnetism, Kyoto, Final Dst index (1957 – 2014), http://wdc.kugi.kyoto-u.ac.jp/dstdir/]

  • FIGURE 8
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    FIGURE 8

    The equivalent vertical delay (in meters) for observations over the conterminous United States (CONUS) at 03:10:30 UTC, October 31, 2003, as sampled by (a) the CORS network and (b) the WAAS network (when WAAS included only 25 stations)

  • FIGURE 9
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    FIGURE 9

    The equivalent vertical delay (in meters) for observations of the CORS network over the conterminous United States (CONUS): (a) April 7,2000, 04:09:00 UTC; (b) July 16, 2000, 04:43:30; (c) April 1, 2001, 04:07:00; (d) October 30, 2003, 03:10:30 UTC; and (e) November 21, 2003, 03:00:00 UTC. The epoch chosen for each figure is roughly 4½ hours after sunset in Miami, Florida.

  • FIGURE 10
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    FIGURE 10

    Schematic diagram of the ionospheric perturbation metric (IPM) as a function of time for an ionospheric storm that trips the Extreme Storm Detector (ESD). The dashed lines represent detector thresholds as they have been defined since WFO Release 3A: the ESD onset and recovery thresholds (TESD,trip and TESD,recovery) are in red; the Moderate Storm Detector (MSD) onset threshold (TMSD,trip) is in magenta (in practice, the MSD recovery threshold TMSD,recovery is set equal to TMSD,trip); and the irregularity detector trip threshold (Tirreg,trip) is in blue. The ESD enters the storm Onset Confirmation State when it crosses TESD,trip. The extreme storm is confirmed when the IPM has remained above TESD,trip for a time duration of tESD,confirm. The ESD enters the Recovery Confirmation State when it crosses TESD,recovery and resumes its normal state after it has remained below TESD,trip for a time duration of tESD,recovery.

  • FIGURE 11
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    FIGURE 11

    Ionospheric perturbation metric (IPM) as a function of time for the moderate storm of October 24, 2011. The area of the region in red defines the ionospheric disturbance index (IDI) used to rank the magnitude of the storm. The dashed lines represent detector thresholds as they have been defined since WFO Release 3A: the ESD onset and recovery thresholds (TESD,trip and TESD,recovery) are in red; the moderate storm detector onset threshold (TMSD,trip) is in magenta; and the irregularity detector trip threshold (Tirreg,trip) is in blue.

  • FIGURE 12
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    FIGURE 12

    Ionospheric perturbation metric (IPM) as a function of time and interpolated map of vertical delay (in m) at the peak of the IPM for the five extreme storms of solar cycle 23: (a) IPM for April 6–7, 2000; (b) vertical delay map for April 6–7, 2000; (c) IPM for July 15–16, 2000; (d) vertical delay map for July 15–16, 2000; (e) IPM for March 31, 2001; (f) vertical delay map for March 31, 2001; (g) IPM for October 29–31, 2003; (h) vertical delay map for October 29–31, 2003; (i) IPM for November 20–21, 2003; and (j) vertical delay map for November 20–21, 2003. Note that the length of each x-axis in the plots of IPM vs. time varies from storm to storm.

  • FIGURE 13
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    FIGURE 13

    The number of minutes that the MSD is in a tripped state for the data interval January 6, 2011, to November 13, 2013

  • FIGURE 14
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    FIGURE 14

    The ionospheric disturbance index (IDI) for various storms occurring in (a) solar cycle 23 (defining the IDI using kriging estimation [WFO Release 3A] and planar fit estimation [Release 8/9.2]) and (b) solar cycle 24 (defining the IDI using kriging estimation). Note the different scales in each plot used for the x-axis.

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    TABLE A1

    A history of updates to storm-related operational system parameters.

    ReleaseIOCLPV Release 6/7LPV Release 8/9.2WFO Release 3ARelease 46-CY16Release 51-CY18
    Date of release7/10/20039/27/20079/22/200810/20/20118/24-27/20169/11-14/2018
    Number of stations253438383838
    WAAS IGP mask002003004005006007
    Number of IGPs190321317318306306
    Fit measurementsuncorrelateduncorrelateduncorrelatedcorrelatedcorrelatedcorrelated
    hi350 km350 km350 km350 km350 km350 km
    Embedded Image35 cm35 cm35 cm30 cm30 cm30 cm
    Embedded Image35 cm35 cm35 cm1 m1 m1 m
    ddecorrNANANA8000 km8000 km8000 km
    Rmax, Rmin2100, 800 km2100, 800 km2100, 800 km2100, 800 km2100, 800 km2100, 800 km
    Ntarget, Nmin30, 1030, 1030, 1030, 1030, 1030, 10
    λW, φWNA130°W, 26.75°N130°W, 21.75°N130°W, 21.75°N130°W, 21.75°N130°W, 21.75°N
    λM, φMNA80°W, 18°N80°W, 13°N80°W, 13°N80°W, 13°N80°W, 13°N
    λE, φENA60°W, 18°N60°W, 13°N40°W, 13°N40°W, 13°N40°W, 13°N
    Pfa10-310-310-310-310-310-3
    RnoiseNoYesYesYesYesYes
    Rirregstaticdynamicdynamicdynamicdynamicdynamic
    Tirreg, trip12.52.53.03.03.0
    tirreg, hyst15 min30 min30 min30 min30 min30 min
    GIVEmax45 m45 m45 m45 m45 m45 m
    TESD,tripNA5050323232
    tESD,confirmNA1 hr1 hr1 hr1 hr1 hr
    TESD,recoveryNA4545292929
    tESD,recoveryNA8 hr8 hr8 hr8 hr8 hr
    TMSD,tripNANANANA1010
    tMSD,confirmNANANANA10 min10 min
    TMSD,recoveryNANANANA1010
    tMSD,recoveryNANANANA10 min10 min

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NAVIGATION: Journal of the Institute of Navigation: 69 (1)
NAVIGATION: Journal of the Institute of Navigation
Vol. 69, Issue 1
Spring 2022
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WAAS and the Ionosphere – A Historical Perspective: Monitoring Storms
Lawrence Sparks, Eric Altshuler, Nitin Pandya, Juan Blanch,, Todd Walter
NAVIGATION: Journal of the Institute of Navigation Mar 2022, 69 (1) navi.503; DOI: 10.33012/navi.503

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WAAS and the Ionosphere – A Historical Perspective: Monitoring Storms
Lawrence Sparks, Eric Altshuler, Nitin Pandya, Juan Blanch,, Todd Walter
NAVIGATION: Journal of the Institute of Navigation Mar 2022, 69 (1) navi.503; DOI: 10.33012/navi.503
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  • Article
    • Abstract
    • 1 INTRODUCTION
    • 2 ESTIMATION OF IONOSPHERIC DELAY
    • 3 SELECTION OF MEASUREMENTS TO BE FIT
    • 4 DETECTION OF LOCAL MESOSCALE IRREGULARITIES
    • 5 COMPACT MESOSCALE IRREGULARITIES ARISING FROM EXTREME STORMS
    • 6 DETECTION OF EXTREME STORMS
    • 7 DETECTION OF MODERATE STORMS
    • 8 RANKING STORM MAGNITUDES
    • 9 SUMMARY
    • HOW TO CITE THIS ARTICLE
    • ACKNOWLEDGMENTS
    • APPENDIX A: RELEASE HISTORY OF STORM-RELATED OPERATIONAL SYSTEM PARAMETERS
    • REFERENCES
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Keywords

  • geomagnetic storms
  • Global Navigation Satellite System (GNSS)
  • ionosphere
  • satellite-based augmentation systems (SBAS)
  • Wide Area Augmentation System (WAAS)

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