Transcript PowerPoint Presentation - 12.540 Principles of the Global

Chapter 8: The future geodetic
reference frames
Thomas Herring, Hans-Peter Plag, Jim Ray,
Zuheir Altamimi
Status
• The method of realizing the geodetic reference frame is still
being debated.
• Current sections:
– 8.1 Concepts of frame and system
– 8.2 Reference frame formulation
– 8.3 Linking geodetic measurements
– 8.4 Potential field and geometric frames
– 8.5 Time variation of reference frame
– 8.6 Components needed for reference frame
– [8.7 Solar system dynamic reference frames?] -- Should be
included in 8.1, and 8.3.
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8.1 Concepts
• Two systems needed: Terrestrial rotating system and
external inertial system.
• The terrestrial reference system is based on
potential. Given a Cartesian frame, time dependent
mass elements are assigned to each X,Y,Z
coordinate. The integrals of potential for this system
are divided into solid-Earth, fluid core and outer fluid
envelope.
• Surface coordinates correspond to surface mass
elements and in a consistent formulation, gravity and
position changes are related. The problem is how to
determine the motion of the mass elements?
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Concepts
• Ideally, all forces and rheologies of system would be known and
motions can be computed.
• Earth rotation variations would be the degree-1 toroidal
components, averaged over a specific region, such as crustal
layer, of the deformation field.
• Many of these forces are ready well known (e.g., tides), others
such as plate tectonic forces can be approximated, and others
are not well known but can be inferred from geodetic
measurements (hydrographic loading)
• Develop a reference system that allows inputs from different
geodetic components to realize the frame. Example next slide.
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Example Concept
• Hydrographic/Atmospheric loading:
– Atmospheric load from metrological analysis fields
– Gravity missions such as GRACE measure changes in
gravity which are interpreted as surface load changes.
– The mass changes in the fluid envelope cause deformations
in the solid Earth
– The instantaneous realization of the reference frame would
incorporate the loading deformations associated with the
gravity changes accounting for the effects of the loading on
the satellite tracking and EOP.
• This would be one effect of many. Other effects would be
earthquake generated signals, atmospheric loading, internal
stress changes in the Earth.
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Height estimates at WILL from PBO combined data product
RMS scatter 3.7 mm (no corrections)
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dHeight (mm)
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0
-5
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dU Will PBO
Atmospheric loading
Other mass from GRACE
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2005.0
2005.5
GGOS
2006.0Chapter 8
Year
2006.5
2007.0
6
Zoom during winter of 2006
Notice high correlation of estimates with atmospheric pressure loading.
Brown curve is load signal from other mass inferred from the GRACE mission.
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dHeight (mm)
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0
-5
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dU Will PBO
Atmospheric loading
Other mass from GRACE
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2005.7
2005.8
2005.9 GGOS Chapter
2006.0 8
Year
2006.1
2006.2
7
2006.3
Data obtained from the University of Colorado
GRACE website:
geoid.colorado.edu/grace/grace.php
GRACE Expected load anomaly September 2006
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Data obtained from the University of Colorado
GRACE website:
geoid.colorado.edu/grace/grace.php
Grace load anomaly April 2006
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Amplitude of annual of load signal
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RMS residual load signal after annual removed
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8.2 Reference Frame Formulation
• Temporal variations of site coordinates will be complex in
general and as more is learned about the Earth, the motion
complexity will increase.
• Sites would be divided into two types:
– “Frame realization” sites that would have “simple, well
characterized motions” (plate motion, GIA, loading not too
effected by ocean effects).
– Reference frame sites that could have more complicated
motions (e.g., earthquake postseismic) but are needed to
allow user local access to the reference frame.
• Anomalous station motion would be defined as a deviation of
observed motion from predicted motion.
• Enough redundancy in the frame realization sites is needed to
allow the detection of anomalous motion.
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8.3 Linking geodetic measurements
• Section to discusses issues of linking ground
geodetic systems to satellite and celestial systems
• Linkage of geodetic systems e.g., collocation of
ground systems versus linkage through orbits (corner
cubes in satellites)
• Inertial frame from quasars and solar system
dynamics
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8.4 Potential and Geometric
reference frames
• Orthometric heights versus ellipsoidal heights
• In reference system definition, the gravimetric
concept is imbedded however spatial resolution may
not be adequate? Depends on future missions
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8.5 Time variations of reference
frame
• Summary of the magnitudes of changes expected
from various signals:
– Plate tectonics
– Glacial isostatic adjustment
– Tidal (earth and ocean and ocean loading)
– Loading atmosphere, hydrology, fluid core
• Document effects on position, rotation and gravity
• Most of this information is in other chapters
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8.6 Components needed
• Section looks at temporal, spatial resolutions and
latency need from frame resolution.
• Temporal and spatial resolution possible with future
gravity missions
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