E. C. Pavlis Geoscience Australia Seminar Canberra, Australia 29 August, 2005 Implications of SLR Network Variations On Geodetic and Geophysical Products

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Geoscience Australia Seminar

Canberra, Australia

29 August, 2005

Implications of SLR Network VariationsOn

Geodetic and Geophysical Products

Erricos C. PavlisJoint Center for Earth Systems Technology / JCETUniversity of Maryland Baltimore County / UMBC

Geoscience Australia Seminar 2005 2E. C. Pavlis QuickTime™ and aPhoto - JPEG decompressor


Earth -- A Dynamic PlanetEarth -- 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



Space Geodetic Science and TechnologySpace Geodetic Science and TechnologyEnables Global Millimeter-level Measurements ofEnables Global Millimeter-level Measurements of

Earth Dynamics, Oceanography, Polar/Ice Science, Land Surface ChangeEarth Dynamics, Oceanography, Polar/Ice Science, Land Surface Change

Very Long BaselineVery Long BaselineInterferometryInterferometry

(VLBI)(VLBI)

Satellite LaserSatellite LaserRangingRanging

(SLR)(SLR)

Global PositioningGlobal PositioningSystem System

(GPS)(GPS)

•Polar Motion Polar Motion •Length of DayLength of Day•Inertial ReferenceInertial Reference•30 Station Network30 Station Network

Network Organization:Network Organization:International VLBI ServiceInternational VLBI Service

• Satellite Positioning < 3 cmSatellite Positioning < 3 cm• Time Variable GravityTime Variable Gravity• Earth Center of MassEarth Center of Mass• ~40 Station Network~40 Station Network

Network Organization:Network Organization:International Laser Ranging International Laser Ranging ServiceService

• Satellite Positioning <10 Satellite Positioning <10 cmcm• Polar motionPolar motion• Site velocitySite velocity•>250 Station Network>250 Station Network

Network Organization:.Network Organization:.International GPS ServiceInternational GPS Service



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Satellite Laser Ranging (SLR)Satellite Laser Ranging (SLR)GRAVITY (Earth)

DYNAMICS (Satellite Orbits)

GEOMETRY (Ranges from stations)

ANALYSIS (Math. & Stat. Physical Model)

Geodetic & Geophysical ParametersGeodetic & Geophysical Parameters













Network Changes Affect the Quality of: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)

– …



Geophysics impacted in various ways: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.



SLR Weekly Analysis Scheme

CDDIS/EDC

AnalysisCenter

LAGEOS 1

ETALON 2

ETALON 1

LAGEOS 2

LAGEOSNEQs

ETALONNEQs

LAGEOS +

ETALONNEQs

Relative weighting

ACCUMULATEDNEQs OF LAGEOS

AND ETALONFROM PREVIOUS

WEEKLYREDUCTIONS

•STATION COORDINATES•STATION VELOCITIES•EOP SERIES (DAILY SINCE 1993)•WEEKLY DEGREE-1 HARMONICS•WEEKLY SECOND DEGREE • HARMONICS•ORBITAL PARAMETERS, …

PRODUCTSPRODUCTS

DATADATA



Typical Weekly SLR Data SetTypical Weekly SLR Data Set





• 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 ExperimentNetwork Perturbation Experiment



Multi-year Test AnalysisMulti-year Test Analysis1993

19941995

19961997

19981999

20002001

20022003

+

+

++

+

+

+

+

+

+

= Results= Results

???? = Year with modified SLR network

???? = Year with real SLR network



Standard - 2

Standard - ALL

20032003



Definition of the

TTerrestrial

RReference

FFrame - TRF



0

30

60

90

0

30

60

90

120

210

240

270

300

330

ILRS Network 2003: Standard

North Sites

South Sites 0

30

60

90

0

30

60

90

120

210

240

270

300

330

ILRS Network 2003: Standard - NASA Sites

North Sites

South Sites

0

30

60

90

0

30

60

90

120

210

240

270

300

330

ILRS Network 2003: Standard - Hawaii & Arequipa

North Sites

South Sites

ALL

2 sites



Geocenter Monitoring

(COM)



Terrestrial SpaceTerrestrial SpaceGeocenter -- Reference Frame OriginGeocenter -- Reference Frame Origin



Unique contribution from SLRUnique contribution from SLR



COM Component STD - 2 STD - ALL AccuracyAccuracy

∆X[mm]

µ -2.3 -7.7 33

50 - 100 %50 - 100 %RMS 4.6 6.0

∆Y[mm]

µ 0.2 6.5 33

50 - 100 %50 - 100 %RMS 6.0 4.7

∆Z[mm]

µ 8.4 10.0 55

100 - 100 - 200%200%RMS 11.4 16.1

COM Variation Compared to Present Accuracy



TRF Component STD - 2 STD - ALL

AccuracyAccuracy

(over 10y)(over 10y)

∆VX

[mm/y]

µ -0.7 -0.5 1.51.5

300-400%300-400%RMS 7.2 6.6

∆VY

[mm/y]

µ 1.6 0.4 1.51.5

300-400%300-400%RMS 29.7 6.4

∆VZ

[mm/y]

µ 2.4 2.4 4.04.0

400 %400 %RMS 20.1 20.1

TRF Changes Compared to Present Accuracy



EEarth

OOrientation

PParameters

-- EOP







y

Inertial Space --Inertial Space --AstrometryAstrometry

Terrestrial Space --Terrestrial Space --Satellite TechniquesSatellite Techniques











North Pole ViewNorth Pole View South Pole ViewSouth Pole View

WEST EASTEAST WEST

Day 1Day 1

Day 2Day 2



EOP Component STD - 2 STD - ALL AccuracyAccuracy

∆x[mas]

µ 0.41 0.58 0.150.15

200-300%200-300%RMS 0.52 0.70

∆y[mas]

µ 0.16 -2.17 0.150.15

200-300%200-300%RMS 0.28 0.67

∆LOD[µts]

µ 8.2 -3.2 5050

100-200%100-200%RMS 100.5 128.8

EOP Variation Compared to Present Accuracy



Temporal Variations of

Gravity

Long wavelength



Harmonic Component STD - 2 STD - ALL AccuracyAccuracy

J2 x 1011 RMS 6.4 6.633

~ 100 %~ 100 %

C(2,1) & S(2,1)x 1010

RMS 4.3 & 2.8 5.8 & 7.01.3 & 1.11.3 & 1.1

200-500%200-500%

C(2,2) & S(2,2)x 1011

RMS 22 & 18 34 & 267.1 & 3.67.1 & 3.6

200-400%200-400%

TVG Variation Compared to Present Accuracy



Mean Sea Level RateJASON / 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.



Impact of Improved TOPEX Orbits…

…from Improved Reference Frame

Before …Before … … … AfterAfterAscending/DescendingAscending/Descending

Mean ± = 152.5 ± 7.8

mm Mean ± = 152.5 ± 5.7 mm

S. B. Luthcke & B. Beckley

2.1 mm REDUCTION in RMS2.1 mm REDUCTION in RMS

Compare this to 1.8 to 3.1 mm/y MSL Rise Estimates !!!Compare this to 1.8 to 3.1 mm/y MSL Rise Estimates !!!



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)

Documents

E. C. Pavlis Geoscience Australia Seminar Canberra, Australia 29 August, 2005 Implications of SLR Network Variations On Geodetic and Geophysical Products