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Applications for Precision GPS: Seismology, Volcanic Eruptions, Ice Sheet Dynamics, and Soil Moisture. Kristine M. Larson Dept. of Aerospace Engineering Sciences University of Colorado [email protected]. Outline. Traditional solid Earth geophysical applications of GPS - PowerPoint PPT Presentation
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Applications for Precision GPS: Seismology, Volcanic Eruptions, Ice Sheet Dynamics,
and Soil Moisture
Kristine M. LarsonDept. of Aerospace Engineering Sciences
University of [email protected]
Outline
• Traditional solid Earth geophysical applications of GPS
• Space Weather (briefly)• Ice Sheets • Earthquakes • Volcanoes • Soil Moisture
Start with 24-hour averaged positions using dual-frequency receivers
And then you wait.
Plate Boundary Deformation
GSI
ITRF2005 Altamimi et al., 2007
Global Plate Motions
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).
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.
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.
Ice sheet velocities in Greenland
• Install poles; measure position.
• Return following year; remeasure position; compute velocity.
Thomas et al., 2000
Installed a GPS receiver on the ice
Number of days where temperature was above freezing.
Zwally et al., 2002.
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
Geodetic Challenges• Multipath (reflected signals) is important (and doesn’t
difference out).
Oscillations in position time series reflect different multipath environments
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?
Repeat Times Vary by Satellite
Choi et al., 2004
Repeat Times Vary by Day of Year
See the GPS Tool Box for code to calculate repeat times.
Does it Really Matter?
multipath
Badly corrected multipath
GPS Seismograms
Miyazaki et al., 2004; Emore et al., BSSA, 2007.
East
Advantages of GPS seismology
Another advantage of subdaily GPS
Earthquake
Postseismic
Each point is a 24-hr average
Great earthquakes are often more complicated than this
M8
M7.4
Past two years:55 cm extension
25 cm uplift
Dike intrusionDeflation
Larson and Miklius, in preparation
cm
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.
Soil Moisture
day of year
QuickTime™ and a decompressor
are needed to see this picture.
160 210 260
Kurc and Small, 2004
PBO Site Marshall, CO
Larson et al., GPS Solutions, 2007
The data are free.
And many other networks
Conclusions
• 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.
Acknowledgements
• Co-authors• NSF, NASA, JSPS• IGS & ITRF• UNAVCO,
NEHRP, NGS, USGS, CORS, GEONET, NRCAN, SOPAC, CDDIS, IRIS, EUREF, SCIGN, GIPSY.