Description of static GNSS techniques, applications and societal benefits

1. Static GNSS
Vince Cronin (Baylor University) & Shelley Olds (UNAVCO)
Revisions by Beth Pratt-Sitaula (UNAVCO) and Benjamin Crosby (ISU)
Version June 8, 2017

2. Motivations for this lecture
1. Distinguish static GNSS techniques from others
2. Distinguish static GNSS products from others
3. Outline societal benefits
(Image: Ben Crosby)

3. • Long-duration occupations over well-monumented
marks
Permanent stations are fixed using deep anchors and run
continuously
Campaign stations are revisited infrequently (~1/year) and
occupied for 8 to 48 hours
• Data is always differentially corrected in post-
processing using data from other nearby GNSS stations
Low Precision: OPUS
High Precision: GAMIT, GLOBK, and TRACK
• Highest quality antennas and receivers
Static GNSS techniques

4. Static GNSS stations
• > 20,000 static stations with more added all the time
• Some data freely available, some not
• GNSS = Global Navigation Satellite System
https://www.unavco.org/science/snapshots/solid-earth/2015/kreemer.html

5. Plate Boundary Observatory (PBO)
PBO involves installation, operation, and maintenance
of >1100 continuously operating high-precision GPS
stations (plus >170 other instruments: strainmeters,
borehole seismometers, and tiltmeters)
http://www.unavco.org/instrumentation/networks/status/pbo

6. What is possible with static
GNSS products?
• Spatial positions within a few millimeters.
Requires intensive, high-precision processing
• Thus . . . can track very small changes
Plate motions
Deformation due to hydrology
 Snow or reservoir loading
 Groundwater withdraw
Deformation due to volcanic activity
 Pre-eruption doming
 Caldera collapse
Earthquake motions
 Slow slip and coseismic deformation

7. Two PBO stations in
California
• Twenty-nine
Palms,(BEMT)
• Mission Viejo (SBCC)
Where is that chunk of crust
going?
• Example: using GPS velocities to understand
plate motions

8. http://www.unavco.org/instrumentation/networks/status/pbo/overview/SBCC
• Station position over time
North–South
East–West
Up–Down
GPS time-series data

9. • From the changing
position, velocity can be
calculated using slope
(rise-over-run)
http://www.unavco.org/instrumentation/netwo
rks/status/pbo/overview/SBCC
GPS time-series data
19 years
510 mm
north
26.8 mm/yr
475 mm
west
25.0 mm/yr
~0.4 mm/yr
~8 mm down

10. 19 years
510 mm
north
26.8 mm/yr
475 mm
west
25.0 mm/yr
~0.4 mm/yr
~8 mm down
PBO also supplies “detrended” data with the average velocity subtracted out to
observe other phenomena. In that case official velocity is given.
Detrended GPS time data

11. What is a site’s 3D speed?
Using the Pythagorean Theorem (high school math...),
Speed = (27.8)2 + (25.7)2 + (1.3)2 = 37.9 mm/yr

12. Using the horizontal components of velocity,
and a bit of high school trigonometry…
What compass direction is
the site moving?
42.8°west of north
or
317.2°azimuth
θ = tan-1(25.7/27.8) = 42.8°
θ
27.8 mm/yr
25.7 mm/yr
North
West

13. Map view of velocity
20 mm/yr

14. Two different velocities
Same process yields much slower velocity at BEMT
20 mm/yr
Why the difference?

15. San Andreas Fault!
20 mm/yr

16. Reference Frames
All velocities are
RELATIVE to a given
reference frame
• Velocities
compared to
International
Terrestrial
Reference Frame
2008 (IGS08 is GPS
reference frame
name)
• Hot spot
constellation as
“stable”

17. Reference frames
All velocities are
RELATIVE to a given
reference frame
• Velocities
compared to stable
North America
(called NAM08
reference frame)
• Eastern North
America as “stable”

18. Societal benefits
• Static GNSS data are used in a wide variety of surface
deformation applications.
• Some are directly supporting human needs
Tracking hazardous features such as landslides, faults, or
volcanos
Tracking changes in water resources
• Some are indirectly providing insight into the way the
earth works
Plate motions
Discovering new faults
• Some static, continuous sites are used for corrections
to other GNSS data, aiding industry.

19. Societal value of
GNSS-enabled research
• Most people use it for location and navigation,
but how do earth scientists use GNSS?
Think-Pair-Share discussion
How do earth scientists use GNSS?
 List as many applications as you can.
How do these uses benefit society?
 Categorize each as a direct or indirect benefit.
– Direct benefits are immediate and improve lives
– Indirect benefits help humans, but are a few steps removed

20. Societal value of
GNSS-enabled research
• Most people use it for location and navigation,
but how do Earth Scientists use GNSS?
How do earth scientists use GNSS?
 (type student applications here)
How do these uses benefit society?
 Direct
– (type student benefits here)
 Indirect
– (type student benefits here)