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New Scientific Applications with Existing CGPS Capabilities

New Scientific Applications with Existing CGPS Capabilities. Earthquakes, Soil Moisture, and Environmental Imaging. Andria Bilich Geosciences Research Division National Geodetic Survey. Overview. New uses of existing geodetic networks and stations (CORS, IGS, etc.) Earthquakes / seismograms

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New Scientific Applications with Existing CGPS Capabilities

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  1. New Scientific Applications with Existing CGPS Capabilities Earthquakes, Soil Moisture, and Environmental Imaging Andria Bilich Geosciences Research Division National Geodetic Survey

  2. Overview • New uses of existing geodetic networks and stations (CORS, IGS, etc.) • Earthquakes / seismograms • High-rate GPS • Example: 2002 Denali Fault event • Soil moisture • Near-field multipath • Example: Uzbekistan • Environmental imaging • Near- and far-field multipath • Examples: Mauna Kea and Canada

  3. Earthquakes withHigh-Rate GPS • GPS/GNSS positioning • No upper limit to amplitude • No preset ‘frequency response’ • Positions can be computed at every data epoch, independently • Precise and accurate displacements • Well-defined reference frame • Earthquakes • Static and transient deformations • Potentially large magnitude • Frequencies = seconds to hours

  4. GPS Data Rates and Analysis Strategies

  5. Denali Earthquake2002 November 3 USGS fact sheet • Long strike-slip rupture • Magnitude 7.9 • Shallow • SE directivity • Large surface waves USGS fact sheet

  6. Clipped Seismometers+ 1-Hz GPS Many broadbands in western North America went off scale… … and high-rate GPS fills in the gaps

  7. 25 GPS stations 1 sample per second Different azimuths and distances Denali GPS Seismograms

  8. GPS-Seismometer Comparison

  9. Take-home lessons:High-rate GPS/GNSS • GPS and seismometers have complementary strengths/weaknesses • Noisy GPS • Off-scale seismometers • Possible only through GNSS technology advances: data storage, chipsets, firmware, etc. • Existing HR GPS networks expanding…

  10. And now for something completely different…

  11. Multipath Background • What is multipath? • Site-specific • Time-varying • Sensitive to environmental changes • How can we measure multipath? • Pseudorange data combination • Solution residuals • Signal-to-noise ratio

  12. Signal-to-Noise Ratio (SNR) • Measure of signal strength • Total SNR = direct plus reflected signal(s) • Direct amplitude = dominant trend • Multipath signal = superimposed on direct

  13. Soil Moisture from Near-Field Multipath • Existing GPS stations! • Ground reflections • Amplitude attenuation at ground • Soil moisture affects attenuation (reflection coefficient) • Method = monitor SNR amplitude changes over time Larson et al., GPS Solutions, 2007.

  14. Take-home lessons:Soil Moisture • Possible to use existing CGPS monuments and receivers • SNR always computed, sometimes reported • S1,S2 = archived in RINEX • Challenges and issues: • SNR data quality • Antenna gain pattern effects • Satellite power • Vegetation, temperature effects • Sensing depth and footprint

  15. Environmental Imaging with Near- & Far-field Multipath • Extension of soil moisture principles… • SNR data • Reflection strength from multipath amplitude • … plus frequency content of SNR • Satellite motion creates time-varying signature •   h (fast = far; slow = close) • Power spectral maps • Frequency and amplitude with respect to satellite position (elevation/azimuth) • Projected onto map of antenna environment

  16. Mauna Kea (MKEA), Hawaii

  17. MKEA Power Maps 30-60s 10-30s 60-90s • Long periods at low satellite elevation angles • Shorter periods at high elevation angles • High power returns from cinder cones

  18. Dual-FrequencyPower Spectral Maps Churchill (CHUR), Manitoba, Canada S1 S2 Reflection from distant object (building?) Reflection from nearby object (rock outcrops?)

  19. Take-home lessons:Environmental Imaging • Assess multipath environment • Frequency: distance to object • Amplitude: magnitude of errors due to object • Consider position errors at different frequencies (think high-rate GPS positioning) • No new equipment • SNR routinely recorded • … but need precise and accurate SNR related to multipath model (not always possible)

  20. Summary • Existing CGPS networks extended to unforeseen science applications • Sensing soil moisture • Understanding reflections and potential sources of error • Measuring displacements from short-period, transient phenomena

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