itrf origin: diagnosis of current...
TRANSCRIPT
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ITRF origin: Diagnosis of current realization
Danan Dong, Jet Propulsion Laboratory, Caltech
Peng Fang, Scripps Orbit and Permanent Array Center, UCSD
EGU 2007 meeting
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Motivation
• Understand the current status of the realized ITRF origin definition and accuracy
• Explore potential causes for the apparent bias and drift of the ITRF2005 origin relative to ITRF2000 frame
• Discuss the potential approaches to stabilize the reference frame origin in the future
EGU 2007 meeting
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Realization of ITRF origin
• The origin of ITRF is at the center of mass (CM) of the entire Earth including the oceans and atmosphere.
• The ITRF origin is represented through a set of globally distributed station coordinates and velocities
• The ITRF2005 origin is realized by zero translation and translation rate between ITRF2005 and ILRS (SLR) time series
• The accuracy of realized ITRF2005 origin is evaluated through its consistency with respect to ITRF2000
EGU 2007 meeting
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SLR Origin and Scale Variations WRT ITRF2000
By courtesy of Zuheir Altamimi, AGU 2006 talk
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Potential causes for the SLR origin drift wrt ITRF2000 frame
• Geophysical processes (real drift)
• Limited SLR stations with poor geographic network distribution
• Shrinking SLR network, ageing instruments, and unsolved systematic errors
• Non-linear behavior in individual SLR station coordinate solution time series
EGU 2007 meeting
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SLR network
EGU 2007 meeting
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Large mass redistribution on the Earth causes geocenter motion
From Cheng of CSR (2007)
From Univ. of Colorado web site
From NASA/JPL, Kwok (2007)
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Derive SLR origin and scale time series wrt ITRF2000 frame -- our tests
• ILRS CGS weekly solutions (1992.9-2005.9) ILRS DGFI weekly solutions (1992.9-2005.9)
• Adopt Kalman filter approach to stack the data and impose the minimum constraints
Assign weekly network parameters as global parameters instead of stochastic parameters
• Following the procedures of Altamimi (2006)
• Treat coordinates and velocities for Stations Simens (1873 and 1893), San Fernando (7824) and Arequipa (7403) empirically
EGU 2007 meeting
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ILRS CGS origin and scale wrt ITRF2000 frame
EGU 2007 meeting
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ILRS dgfi origin and scale wrt ITRF2000 frame
EGU 2007 meeting
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EGU 2007 meeting
-0.07-0.5 1.8 -0.1 0.2 5.8 0.8 -0.1official
-0.003 0.04 1.1 0.5 -0.4 3.3 3.9 0.6DGFI
-0.017 0.18 0.3 0.2 -0.4 3.9 -6.2 -1.4CGS
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solution
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Considerations of stabilizing reference origin
• Research on the non-linear behavior of the station coordinate solutionsreal: geophysical process, in particular large scale
mass redistribution not real: systematic errors
• Enlarge SLR network to improve the distribution and to avoid overly rely on few stationslobby congress?
• Consider adding other technique solutions GPS?
EGU 2007 meeting
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Reduce systematic errors in GPS data analysis
• Improve various models currently used in GPS data analysis
• Antenna phase center variation model
• Second-order ionosphere correction
• ‘GPS year’ errors
• Deal with the spatially non-uniform station distribution: weighted by Voronoi cells
• Common-mode-errors (CME)
EGU 2007 meeting
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East CME from global GPS network
EGU 2007 meeting
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Summary
• The current assessment about the ITRF2005 origin consistency may be relatively conservative
• The main causes for the SLR determined origin inconsistency are: limited number of stations, poor network geometry distribution, and non-linear behavior in the station coordinate time series
• Avoid overly relying on a few stations to determine the frame origin: before it becomes too late
EGU 2007 meeting