1. E. C. Pavlis Geoscience Australia Seminar Canberra, Australia 29 August, 2005 Implications of SLR Network Variations On Geodetic and Geophysical Products Erricos C. Pavlis Joint Center for Earth Systems Technology / JCET University of Maryland Baltimore County / UMBC

2. E. C. Pavlis Geoscience Australia Seminar 2005 2 Earth -- A Dynamic Planet What happens in one location at one time, does not necessarily happen at all places, but … … it affects other places through the continuous interaction between the components of System Earth

3. E. C. Pavlis Geoscience Australia Seminar 2005 3 Space Geodetic Science and Technology Enables Global Millimeter-level Measurements of Earth Dynamics, Oceanography, Polar/Ice Science, Land Surface Change Very Long Baseline Interferometry(VLBI) Satellite Laser Ranging (SLR) (SLR) Global Positioning System(GPS) Polar MotionPolar Motion Length of DayLength of Day Inertial ReferenceInertial Reference 30 Station Network30 Station Network Network Organization: International VLBI Service Satellite Positioning < 3 cm Satellite Positioning < 3 cm Time Variable Gravity Time Variable Gravity Earth Center of Mass Earth Center of Mass ~40 Station Network ~40 Station Network Network Organization: International Laser Ranging Service Satellite Positioning <10 cm Satellite Positioning <10 cm Polar motion Polar motion Site velocity Site velocity >250 Station Network>250 Station Network Network Organization:. International GPS Service

4. E. C. Pavlis Geoscience Australia Seminar 2005 4 Satellite Laser Ranging (SLR) GRAVITY (Earth) DYNAMICS (Satellite Orbits) GEOMETRY (Ranges from stations) ANALYSIS (Math. & Stat. Physical Model) Geodetic & Geophysical Parameters

5. E. C. Pavlis Geoscience Australia Seminar 2005 5

6. E. C. Pavlis Geoscience Australia Seminar 2005 6

7. E. C. Pavlis Geoscience Australia Seminar 2005 7 Earth’s Tectonic Plates -- First Complication … a minimum of three sites per plate per network Network DesignNetwork Design

8. E. C. Pavlis Geoscience Australia Seminar 2005 8 Earth’s Gravity -- Second Complication … varying over the globe AND in time! Network DesignNetwork Design

9. E. C. Pavlis Geoscience Australia Seminar 2005 9 Funding for Science -- Third Complication … scientific networks operate through international agreements between national agencies, but are always prone to local and global economic trends and priorities. Network DesignNetwork Design

10. E. C. Pavlis Geoscience Australia Seminar 2005 10  Network Changes Affect the Quality of: –Defined TRF and its Temporal Evolution –Determination of Earth Orientation (EOP) –Monitoring of Geocenter Variations (COM) –Long-wavelength Gravitational Variations (TVG) –Precision Orbital Products (POD) –Scientific Products (e.g. Mean Sea Level rate) –…

11. E. C. Pavlis Geoscience Australia Seminar 2005 11  Geophysics impacted in various ways: –GEOMETRY - sites change network geometry/robustness; –OBSERVATIONS - loss of tracking data over key regions; –MODELS - incomplete description of processes (e.g. gravity); –QUALITY - missing sites & data modify standards for QC; –RESOLUTION - temporal gaps limit resolution of products, (e.g. Earth rotation parameters); –LINKAGE - data are the conduit of information between the system (Earth) and the processes, any loss of data severs this link and limits the effectiveness of the research results.

12. E. C. Pavlis Geoscience Australia Seminar 2005 12 SLR Weekly Analysis Scheme CDDIS/EDC Analysis Center LAGEOS 1 ETALON 2 ETALON 1 LAGEOS 2 LAGEOS NEQs ETALON NEQs LAGEOS + ETALON NEQs Relative weighting ACCUMULATED NEQs OF LAGEOS AND ETALON FROM PREVIOUS WEEKLY REDUCTIONS STATION COORDINATES STATION VELOCITIES EOP SERIES (DAILY SINCE 1993) WEEKLY DEGREE-1 HARMONICS WEEKLY SECOND DEGREE HARMONICS ORBITAL PARAMETERS, … PRODUCTS DATA

13. E. C. Pavlis Geoscience Australia Seminar 2005 13 Typical Weekly SLR Data Set

14. E. C. Pavlis Geoscience Australia Seminar 2005 14 To determine the full effect of changes in a network, we constructed geophysical products based on modified networks; A realistic case has been studied, using the real data collected by the ILRS network between 1993 and 2003; For years 1993, 1996 and 2000, the “dropped” sites vary; For 2003 two variations with respect to the standard were considered: –The standard network minus two sites that were eliminated in early 2004 (Hawaii and Arequipa) -- real case –The standard network with ALL western hemisphere sites eliminated (hypothetical) Network Perturbation Experiment

15. E. C. Pavlis Geoscience Australia Seminar 2005 15 1993 Quincy 7109, Huahine 7123, Zimmerwald 7810, Simosato 7838, Graz 7839, RGO 7840, Orroral 7843 1996 Yarragadee 7090, Mon. Pk. 7110, Changchun 7237, Potsdam 7836, Matera 7939, Wettzell 8834 2000 McDonald 7080, Papeete 7124, Tateyama 7339, Hartebeesthoek 7501,San Fernando 7824, Grasse 7835, Mt. Stromlo 7849 2003 (a)Haleakala 7210, Arequipa 7403 (b)(a)+all W. Hemisphere sites Network Change Scenarios

16. E. C. Pavlis Geoscience Australia Seminar 2005 16 Multi-year Test Analysis 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 + + + + + + + + + + = Results ???? = Year with modified SLR network ???? = Year with real SLR network

17. E. C. Pavlis Geoscience Australia Seminar 2005 17 Sites eliminated in 1993 7109 7123 7843 1993

18. E. C. Pavlis Geoscience Australia Seminar 2005 18 Sites eliminated in 1996 1996

19. E. C. Pavlis Geoscience Australia Seminar 2005 19 2000 Sites eliminated in 2000

20. E. C. Pavlis Geoscience Australia Seminar 2005 20 Standard - 2 Standard - ALL 2003

21. E. C. Pavlis Geoscience Australia Seminar 2005 21 Definition of the T Terrestrial R Reference F Frame - TRF

22. E. C. Pavlis Geoscience Australia Seminar 2005 22 ALL 2 sites

23. E. C. Pavlis Geoscience Australia Seminar 2005 23 Geocenter Monitoring (COM)

24. E. C. Pavlis Geoscience Australia Seminar 2005 24 Terrestrial Space Geocenter -- Reference Frame Origin Unique contribution from SLR

25. E. C. Pavlis Geoscience Australia Seminar 2005 25 COM Component STD - 2 STD - ALLAccuracy ∆X [mm] µ-2.3-7.7 3 50 - 100 % RMS 4.66.0 ∆Y [mm] µ0.26.5 3 50 - 100 % RMS 6.04.7 ∆Z [mm] µ8.410.0 5 100 - 200% RMS 11.416.1 COM Variation Compared to Present Accuracy

26. E. C. Pavlis Geoscience Australia Seminar 2005 26 TRF Component STD - 2 STD - ALLAccuracy (over 10y) ∆V X [mm/y] µ-0.7-0.5 1.5300-400% RMS 7.26.6 ∆V Y [mm/y] µ1.60.4 1.5300-400% RMS 29.76.4 ∆V Z [mm/y] µ2.4 4.0 400 % RMS 20.1 TRF Changes Compared to Present Accuracy

27. E. C. Pavlis Geoscience Australia Seminar 2005 27 E Earth O Orientation P Parameters -- EOP

28. E. C. Pavlis Geoscience Australia Seminar 2005 28  y Inertial Space -- Astrometry Terrestrial Space -- Satellite Techniques

29. E. C. Pavlis Geoscience Australia Seminar 2005 29 North Pole View South Pole View WESTEAST WEST Day 1 Day 2

30. E. C. Pavlis Geoscience Australia Seminar 2005 30 EOP Component STD - 2 STD - ALLAccuracy ∆x [mas] µ0.410.58 0.15200-300% RMS 0.520.70 ∆y [mas] µ0.16-2.17 0.15200-300% RMS 0.280.67 ∆LOD [µts] µ8.2-3.2 50100-200% RMS 100.5128.8 EOP Variation Compared to Present Accuracy

31. E. C. Pavlis Geoscience Australia Seminar 2005 31 Temporal Variations of Gravity Long wavelength

32. E. C. Pavlis Geoscience Australia Seminar 2005 32 Harmonic Component STD - 2 STD - ALLAccuracy J 2 x 10 11 RMS 6.46.63 ~ 100 % C (2,1) & S (2,1) x 10 10 RMS 4.3 & 2.85.8 & 7.0 1.3 & 1.1 200-500% C (2,2) & S (2,2) x 10 11 RMS 22 & 1834 & 26 7.1 & 3.6 200-400% TVG Variation Compared to Present Accuracy

33. E. C. Pavlis Geoscience Australia Seminar 2005 33 Mean Sea Level Rate JASON / TOPEX POD Product based on two TRFs TRF 1:Official T/P Project TRF (CSR’s SSC(CSR)95 L 01) TRF 2:ITRF2000 Study performed by GSFC’s Altimetry Group (Scott Luthcke, Brian Beckley, et al.) and presented at the last JASON SWT, St. Petersburg, Florida.

34. E. C. Pavlis Geoscience Australia Seminar 2005 34 Impact of Improved TOPEX Orbits… …from Improved Reference Frame Before … … After Ascending/Descending Mean ±  = 152.5 ± 7.8 mm Mean ±  = 152.5 ± 5.7 mm S. B. Luthcke & B. Beckley 2.1 mm REDUCTION in RMS Compare this to 1.8 to 3.1 mm/y MSL Rise Estimates !!!

35. E. C. Pavlis Geoscience Australia Seminar 2005 35 Conclusions - Summary Tracking network structure and stability ensures high quality science Though mix of techniques complement each other, each technique needs to maintain minimum standards to be effective Uniformity and stability in time are critical for all products derived from observations collected by each network Even a seemingly mild intervention in the SLR network (elimination of Hawaii and Arequipa), results in changes that are significant compared to presently attainable accuracy More severe changes, resulting in a lopsided network (elimination of Yarragadee), result in entirely erroneous results Long-wavelength errors in the TRF, EOP, COM, POD, SSH, etc. can be mistakenly interpreted as geophysical signals Global and local geophysics and oceanography that require sub- millimeter accuracy over long time periods are severely affected (e.g. MSL variations)