International Terrestrial Reference System and Frame: Difference between revisions

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The '''International Terrestrial Reference System''' ('''ITRS''') describes procedures for creating [[frame of reference|reference frame]]s suitable for use with measurements on or near the Earth's surface. This is done in much the same way that a [[Standard (metrology)|physical standard]] might be described as a set of procedures for creating a ''realization'' of that standard. The ITRS defines a [[Geocentric coordinate system|geocentric]] system of coordinates using the [[SI]] system of measurement.

An '''International Terrestrial Reference Frame''' ('''ITRF''') is a realization of the ITRS. Its origin is at the center of mass of the whole earth including the oceans and atmosphere. New ITRF solutions are produced every few years, using the latest mathematical and surveying techniques to attempt to realize the ITRS as precisely as possible. Due to [[experimental error]], any given ITRF will differ very slightly from any other realization of the ITRF. The difference between the latest as of 2006 [[World Geodetic System|WGS 84]] (frame realisation G1150) and the latest ITRF2000 is only a few centimeters and RMS difference of one centimeter per component.<ref>{{cite web |url=http://clynchg3c.com/Technote/geodesy/coorddef.pdf|first=James R. |last=Clynch |title=Earth coordinates |date=February 2006 |website=GPS Geodesy and Geophysics |publisher=James R. Clynch |access-date=24 March 2016}}</ref> ReferenceITRFs epochare was moved from 2000.0 to 2001.0 in G1150 due to alaskan earthquake in November 2002. Still in 2022 ITRF2020 was released[[Earth-centered, yetEarth-fixed GPScoordinate is only using G2139 in its antennassystem|Earth-centered, whichEarth-fixed was(ECEF)]] alignedreference to ITRF2014 (IGb14)frames.

The ITRS and ITRF solutions are maintained by the [[International Earth Rotation and Reference Systems Service]] ([[IERS]]). Practical navigation systems are in general referenced to a specific ITRF solution, or to their own coordinate systems which are then referenced to an ITRF solution. For example, the ''Galileo Terrestrial Reference Frame'' (''GTRF'') is used for the [[Galileo_Galileo (satellite_navigationsatellite navigation)|Galileo]] navigation system; currently defined as ITRF2005 by the [[European Space Agency]].<ref name=gtrf>{{cite web |title=Reference Frames in GNSS |url=https://gssc.esa.int/navipedia/index.php/Reference_Frames_in_GNSS |website=Navipedia |publisher=European Space Agency}}</ref>

== Versions ==

The ITRF realizations developed from the ITRS since 1991 include the following versions:<ref name="QPS">{{cite web|url=https://confluence.qps.nl/qinsy/latest/en/international-terrestrial-reference-frame-2014-itrf2014-138708701.html|title=International Terrestrial Reference Frame 2014 (ITRF2014)|website=Quality Positioning Services B.V.|access-date=3 October 2019}}{{Dead link|date=February 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

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| First solution that combines unconstrained space geodesy solutions free from any [[tectonic plate motion model]].<ref>{{cite journal |last1=Altamimi |first1=Zuheir |last2=Sillard |first2=Patrick |last3=Boucher |first3=Claude |title=ITRF2000: A new release of the International Terrestrial Reference Frame for earth science applications |journal=Journal of Geophysical Research: Solid Earth |volume=107 |number=B10 |doi=10.1029/2001JB000561 |pages=ETG 2-1–ETG 2-19 |year=2002|bibcode=2002JGRB..107.2214A |doi-access=free }}

</ref>

From this version onwards, the motion of the tectonic plate is represented in the solution for each station as a velocity vector. Previous ITRFs only continedcontinued the initial positions, using a motion model to fill in the velocity.

|-

! ITRF2005

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== Users ==

GNSS systems:<ref name=gtrf/>

* [[Galileo_Galileo (satellite_navigationsatellite navigation)|Galileo]] Terrestrial Reference Frame (GTRF), ITRF2005; own implementation using IGS sites.

* [[GPS]] just uses [[WGS 84]], ITRF2020 since January 2024 (but used many versions of 2013WGS 84 before), ITRF2008;a little modified with International GNSS Service (IGS) implementation, IGS20.

* [[BeiDou]] Coordinate System, China Terrestrial Reference Frame (CTRF) 2000 = ITRF97 at epoch 2000.0; own implementation.

* [[GLONASS]] [[PZ-90|PZ-90.11]] is nominally its own system, but is quite close to ITRF and uses many of the same techniques.<ref name=gtrf/>

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* United States: WGS 84 (see above); domestic use is mainly based on [[NAD 83]] instead.

* China: CTRF 2000 per above.

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The GPS reference epoch was moved from 2000.0 to 2001.0 in G1150 due to the magnitude 7.9 Denali Fault earthquake in Alaska in November 2002. Still in 2022 ITRF2020 was released, yet GPS was only using G2139 in its antennas, which was aligned to ITRF2014 (IGb14) (though at epoch 2016.0, not reference epoch 2010.0).<ref name="NOAA2020">{{cite web |last1=US Department of Commerce |first1=National Oceanic and Atmospheric Administration |title=Transitioning from IGS14 to IGb14 - National Geodetic Survey |url=https://geodesy.noaa.gov/CORS/news/igb14/transitioning_to_igb14.shtml |website=geodesy.noaa.gov |access-date=28 June 2022 |language=EN-US}}</ref> On 7 January 2024 move to IGS20 happened, so WGS 84 is now aligned with ITRF2020, including PSD (post-seismic deformation), also called G2296.

On the other hand GLONASS is using PZ-90.11, which is close to ITRF2008 at epoch 2011.0 and is using 2010.0 epoch (that means when you use reference transformation to PZ-90.11 you will get January 2010 date).

== See also ==

* [[Earth-centered, Earth-fixed coordinate system]]

* [[ECEF]]

* [[Earth orientation parameters]]

* [[Geodetic systemdatum]]

* [[International Celestial Reference System and Frameits realizations]]

* [[Terrestrial reference frame]]

* [[World Geodetic System]]

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== External links ==

* [https://itrf.ign.fr/en/solutions/transformations Forward and backward transformations using 14 parameters Helmert]

* [https://www.epncb.oma.be/_productsservices/coord_trans/index.php Convertor between ITRF realisations with changing the epoch and tectonics], [https://www.unavco.org/software/geodetic-utilities/plate-motion-calculator/plate-motion-calculator.html tectonics] for it

* [http://itrf.ensg.ign.fr/general.php What is ITRF?]

* [http://www.iers.org/SharedDocs/Publikationen/EN/IERS/Publications/tn/TechnNote36/tn36_031.pdf?__blob=publicationFile&v=1 Terrestrial reference systems and frames] (PDF; chapter 4 of IERS Conventions 2010)

[[Category:Geodetic datums]]