applications for precision gps: seismology, volcanic eruptions, ice sheet dynamics, and soil...
TRANSCRIPT
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
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
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?
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
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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.
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.