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Kristine M. Larson Dept. of Aerospace Engineering Sciences University of Colorado

Applications for Precision GPS: Seismology, Volcanic Eruptions, Ice Sheet Dynamics, and Soil Moisture. Kristine M. Larson Dept. of Aerospace Engineering Sciences University of Colorado kristinem.larson@gmail.com. Outline. Traditional solid Earth geophysical applications of GPS

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Kristine M. Larson Dept. of Aerospace Engineering Sciences University of Colorado

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  1. Applications for Precision GPS: Seismology, Volcanic Eruptions, Ice Sheet Dynamics, and Soil Moisture Kristine M. Larson Dept. of Aerospace Engineering Sciences University of Colorado kristinem.larson@gmail.com

  2. Outline • Traditional solid Earth geophysical applications of GPS • Space Weather (briefly) • Ice Sheets • Earthquakes • Volcanoes • Soil Moisture

  3. Start with 24-hour averaged positions using dual-frequency receivers And then you wait.

  4. Plate Boundary Deformation GSI

  5. Global Plate Motions ITRF2005 Altamimi et al., 2007

  6. Space Weather Implications • Ambiguity resolution is critical. To the extent that better knowledge of TEC can aid ambiguity resolution, solid Earth geophysicists care about space weather. • Some new applications described in this talk have obvious real-time potential - for which ambiguity resolution is even more important (and challenging).

  7. Space Weather Implications 2 • Many GPS receivers have been installed to catch “once in a career” geophysical signals. Receiver failure because of space weather is always a concern. • For example, my dissertation data were collected in campaigns during June 1986, September 1987, March 1988, and March 1989.

  8. Using GPS at time scales less than a day • Ice sheet speeds, ~100 m/yr (1-2 cm/hr); are they linear? • Earthquakes, 1-100 cm/sec; large accelerations. • Volcanoes, 1-2 cm/hr; not linear, but low accelerations. • Soil moisture, non-traditional GPS application.

  9. Ice sheet velocities in Greenland • Install poles; measure position. • Return following year; remeasure position; compute velocity. Thomas et al., 2000

  10. Installed a GPS receiver on the ice Number of days where temperature was above freezing.

  11. Zwally et al., 2002.

  12. Earthquakes • Global plate velocities are based on ~10 million measurements per site. • Each Greenland (12-hr) ice sheet velocity is based on ~1000 GPS measurements. • For seismic applications, each position is based on 6-10 measurements. Denali, Alaska Earthquake, November 2002

  13. Geodetic Challenges • Multipath (reflected signals) is important (and doesn’t difference out). Oscillations in position time series reflect different multipath environments

  14. Good news: multipath looks the “same” from day to day The GPS orbital period is 1/2 sidereal day, shift time should be 1 sidereal day (or one day minus 236 seconds). Is it?

  15. Repeat Times Vary by Satellite Choi et al., 2004

  16. Repeat Times Vary by Day of Year See the GPS Tool Box for code to calculate repeat times.

  17. Does it Really Matter? multipath Badly corrected multipath

  18. GPS Seismograms East Miyazaki et al., 2004; Emore et al., BSSA, 2007.

  19. Advantages of GPS seismology

  20. Another advantage of subdaily GPS Postseismic Each point is a 24-hr average Earthquake

  21. Great earthquakes are often more complicated than this M7.4 M8

  22. Past two years: 55 cm extension 25 cm uplift Dike intrusion Deflation

  23. cm Larson and Miklius, in preparation

  24. Multipath/Soil Moisture • The frequency of ground multipath (reflections) is determined by the antenna height. • The amplitude of ground multipath is determined by ground reflectance, which can be related to soil moisture content.

  25. 160 210 260 day of year Soil Moisture The data are free. Kurc and Small, 2004 PBO Site Marshall, CO Larson et al., GPS Solutions, 2007

  26. And many other networks

  27. Acknowledgements Conclusions • Co-authors • NSF, NASA, JSPS • IGS & ITRF • UNAVCO, NEHRP, NGS, USGS, CORS, GEONET, NRCAN, SOPAC, CDDIS, IRIS, EUREF, SCIGN, GIPSY. • There are lots of geophysical problems that benefit from high-precision GPS measurements at sub-daily time intervals. • Constellation asymmetry, the troposphere and multipath are currently the limiting error sources.

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