International Terrestrial Reference System ITRS International Terrestrial Reference Frame ITRF

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International Terrestrial Reference System (ITRS)
International Terrestrial Reference Frame (ITRF)

• Zuheir ALTAMIMI
• Laboratoire de Recherche en Géodésie
• Institut Géographique National, France
• E-mail altamimi_at_ensg.ign.fr

AFREF Technical Workshop, University of Cape
Town, July 09-13 , 2006
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Outline

• Intrenational Terrestrial Reference System
• Intrenational Terrestrial Reference Frame
• World Geodetic System 84 WGS84
• Galileo Terrestrial Reference Frame (GTRF)

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International Association of GeodesyAssociated
Space Geodesy Services

• International Earth Rotation and Reference
  Systems Service (IERS) (1988)
• Intern. GNSS Service (IGS) (1994)
• Intern. Laser Ranging Service (ILRS) (1998)
• Intern. VLBI Service (IVS) (1999)
• Intern. DORIS Service (IDS) (2003)

http//www.iag-aig.org/
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International Earth Rotation and Reference
Systems Service (IERS)

• Established in 1987 (started Jan. 1, 1988) by IAU
  and IUGG to realize/maintain/provide
• The International Celestial Reference System
  (ICRS)
• The International Terrestrial Reference System
  (ITRS)
• Earth Orientation Parameters (EOP)
• Geophysical data to interpret time/space
  variations in the ICRF, ITRF EOP
• Standards, constants and models (i.e.,
  conventions)

http//www.iers.org/
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International Terrestrial Reference System (ITRS)
Adopted by IUGG in 1991 for all Earth Science
Applications

• Realized and maintained by ITRS Product Center of
  the IERS
• Its Realization is called International
  Terrestrial Reference Frame (ITRF)
• Set of station positions and velocities,
  estimated by combination of VLBI, LLR, SLR, GPS
  and DORIS individual TRF solutions
• Based on Co-location sites

More than 800 stations located on more than 500
sites
Available ITRF88, 89,,97 Latest
ITRF2000 Coming soon ITRF2005
http//www.ensg.ign.fr/ITRF/
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Co-location Site

• Site where two or more space geodesy close
  instruments (hundred meters) are operating
• Precisely surveyed in three dimensions, using
  classical or GPS geodesy
• Differential coordinates (DX, DY, DZ) are
  available

DX(GPS,VLBI) XVLBI - XGPS
GPS
VLBI
SLR
DORIS
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Current Space Geodesy Networks (1999.0 onward)
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Current Co-locations (1999 onward)
(2)
(16)
(59)
(8)
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International Terrestrial Reference System
(ITRS) Definition

• Origin Center of mass of the whole Earth,
  including oceans and atmosphere
• Unit of length meter SI, consistent with TCG
  (Geocentric Coordinate Time)
• Orientation consistent with BIH (Bureau
  International de lHeure) orientation at 1984.0.
• Orientation time evolution ensured by using a
  No-Net-Rotation-Condition w.r.t. horizontal
  tectonic motions over the whole Earth

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ITRF Datum Definition

• Input
• Global solutions (Positions and Velocities)
  provided by several Analysis Centers (VLBI, SLR,
  GPS, DORIS)
• Local Ties in Co-location Sites
• Datum Definition
• Origin CoM (defined by SLR)
• Scale TCG time scale (VLBI SLR)
• Orientation BIH 1984.0 (alignment of successive
  ITRFs)
• No Net Rotation Condition (Implicit/Conventional)

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Future ITRF solutions

• Based on Time Series of Station Positions
• Daily (VLBI)
• Weekly (GPS, SLR DORIS)
• and Earth Orientation Parameters
• Polar Motion (xp, yp)
• Universal Time (UT1) (Only from VLBI)
• Length of Day (LOD)
• Next Version ITRF2005 to be released soon

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ITRF2005 Co-locations
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ITRF2005 Derivation
W1
W2
Wn

VLBI
TRF (X, V) EOP (SINEX)
SLR
TRF (X, V) EOP (SINEX)
Stacking
GPS
TRF (X, V) EOP (SINEX)
DORIS
TRF (X, V) EOP (SINEX)
Combination ITRF2005
Local Ties
TRF (X, V) EOP (SINEX)
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Datum Definition with Minimum Constraints Over a
Reference Set of stations
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ITRF2005 preliminary results

• Polar Motion
• Origin (Geocenter) and Scale time variations
• Geophysical results
• Plate motions
• Post Glacial Rebound
• Geocenter Motion
• Surface Loading gt Seasonal variation

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Polar Motion
Y(mas)
X (mas)
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Polar motion differences with IERS C04
Xpole
Ypole
VLBI SLR DORIS
GPS
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SLR Origin and Scale Variations WRT ITRF2000
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SLR Origin and Scale Variations
TX(t) A cos(2?t ?)
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Amplitude and Phase of SLR Origin
TX(t) A cos(2?t ?)
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VLBI Scale
WRT ITRF2000
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VLBI vs SLR Scale wrt ITRF2000
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ILRS Network
Number of stations
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VLBI vs SLR Scale wrt ITRF2005
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ITRF2005P to ITRF2000
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ITRF2005 and Plate motionHorizontal Site
velocities with s lt 3mm/y
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Selected sites for plate angular velocities
estimation
Using PB 2002 Plate boundaries (Bird, 2003)
Pacific Africa Amur Antarctica Arabia
Australia Caribbean Eurasia India North
America Nazca Okhotsk South America Somalia
Yangtze
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AFRC (NUBI) EURA Motion
Nubia-Eurasia velocity 50 slower than NUVEL1-A
prediction
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Vertical Velocities Site velocities with s lt
3mm/y
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Dicontinuity Monitoring
Before
After
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Seasonal Variations
Before
After
Real or GPS Artifact ?
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Seasonal Variations GPS/IGS Sites
BAHR
DRAO
IRKT
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GPS Annual Vertical Amplitude Phase
January
A
f
April
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Annual Vertical Amplitude Phase Australia Case
GPS
VLBI
SLR
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Geodetic Signal ?
DORIS
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Geodetic Signal ?
DORIS
SLR
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Geodetic Signal ?
SLR
GPS
DORIS
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Denaly Earthquake (Alaska)
GPS
DORIS
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Arequipa Earthquake
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Arequipa Earthquake
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Access to ITRS

• Direct use of ITRF coordinates
• Use of IGS Products Orbits, Clocks
• all related to ITRF (e.g. use of PPP)
• Fixing or constraining some ITRF station
  coordinates in the analysis of GPS measurements
• Use of transformation formulae

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World Geodetic System 84 (WGS 84)

• Collection of models including Earth Gravity
  model, geoid, transformation formulae and set of
  coordinates of permanent DoD GPS monitor stations
• WGS 60667284
• Originally based on TRANSIT satellite DOPPLER data

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WGS 84

• Recent WGS 84 realizations based on GPS data
• - G730 in 1994
• - G873 in 1996
• TRS of GPS Broadcast Ephemerides
• Coincides with any ITRF at 10 cm level
• For most applications WGS 84 ITRF, but ITRF
  is better realized (a few mm).
• Hope to include NGA stations in the IGS routine
  Analysis

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Galileo Terrestrial Reference Frame (GTRF)

• Galileo Geodesy Service Provider (GGSP)
• GGSP Consortium (GFZ, AIUB, ESOC, BKG, IGN)
• Define, implement maintain the GTRF
• GTRF is Compatible with the ITRF
• Liaison with IERS, IGS, ILRS
• GTRF is a realization of the ITRS
• Similar to IGS/GPS Galileo Orbits, Clocks
• Will be expressed in GTRF (ITRF)

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Provisional Locations of Galileo Sensor Stations
20 GSS for IOV 30 GSS for FOC
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GTRF Implementation

• Initial GSS postionsvelocities will be provided
  using GPS observations
• Subsequent GTRF versions using GPS Galileo
  observations
• Weekly solutions will be performed for the
  long-term maintenance of the GTRF
• independent solutions by the 3 Analysis Centers
  of the GGSP consortium (GFZ, AIUB, ESOC)
• Analysis of the 3 solutions by IGN
• Comparison and quality evaluation
• Combination alignment to the ITRF

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Concluding Remarks

• IAG Services play a major role providing
• geodetic products
• Era of Time series of geodetic products TRF,
  EOP, geocenter motion, etc.
• Geodetic signals for geodynamic applications
• Next ITRF solutions will based on time series
• Well defined and accurate ITRF is always needed
  for the expression of the geodetic results
• Reffinement of the ITRF datum definition will
  continue as appropriate
• Galileo will enhance the ITRF in the future