View source for International Terrestrial Reference System and Frame

{{Short description|World spatial reference system co-rotating with the Earth in its diurnal motion in space}}
[[File:ITRF-Fundamental-u.Satellitenstationen,46 po.jpg|thumb|ITRF reference stations]]
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> ITRFs are [[Earth-centered, Earth-fixed coordinate system|Earth-centered, Earth-fixed (ECEF)]] reference 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 (satellite 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>

{|class = wikitable
! Name
! Ref.
epoch
![[EPSG]]<br />code
! Notes
|-
!ITRF91 
|1988.0
|4913
7903
8991
|
|-
! ITRF92
| 1988.0
| 4914
7904
8992
| First realization of the ITRS
|-
! ITRF93
| 1988.0
| 4915
7905
8993
|
|-
! ITRF94
| 1993.0
| 4916
7906
8994
|
|-
! ITRF96
| 1997.0
| 4917
7907
8995
|
|-
! ITRF97
| 1997.0
| 4918
7908
8996
|
|-
! ITRF2000
| 1997.0
| 4919
7909
8997
| 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 continued the initial positions, using a motion model to fill in the velocity.
|-
! ITRF2005
| 2000.0
| 4896
7910
8998
| Constructed with input data under the form of time series of station positions and Earth Orientation Parameters.<ref name="paper05">{{cite journal |last1=Altamimi |first1=Z. |last2=Collilieux |first2=X. |last3=Legrand |first3=J. |last4=Garayt |first4=B. |last5=Boucher |first5=C. |title=ITRF2005: A new release of the International Terrestrial Reference Frame based on time series of station positions and Earth Orientation Parameters |journal=Journal of Geophysical Research: Solid Earth |volume=112 |pages=B09401 |number=B9 |doi=10.1029/2007JB004949 |year=2007|bibcode=2007JGRB..112.9401A |hdl=10338.dmlcz/141752 |hdl-access=free }}</ref>

This version introduces extra parameters to describe the year-periodic motion of the stations: {{mvar|A}} (amplitude) and {{mvar|φ}} (phase) per-axis. This sort of seasonal variation has an amplitude of around 1&nbsp;cm and is attributed to non-tidal loading effects (e.g. the shifting weight of water).
|-
! ITRF2008
| 2005.0
| 5332
7911

8999
| Includes tropospheric modeling and improved solution methods.<ref name="ITRF2014">{{cite journal|last1=Altamimi|first1=Zuheir|last2=Collilieux|first2=Xavier|last3=Métivier|first3=Laurent|title=ITRF2008: an improved solution of the international terrestrial reference frame|journal=Journal of Geodesy|date=3 February 2011|volume=85|issue=8|pages=457–473|doi=10.1007/s00190-011-0444-4|bibcode=2011JGeod..85..457A|doi-access=free}}</ref>
|-
! ITRF2014
| 2010.0
| 7789
7912 9000
| Generated with an enhanced modeling of nonlinear station motions.<ref>{{Cite journal |last1=Altamimi |first1=Zuheir |last2=Rebischung |first2=Paul |last3=Métivier |first3=Laurent |last4=Collilieux |first4=Xavier |title=ITRF2014: A new release of the International Terrestrial Reference Frame modeling nonlinear station motions |journal = Journal of Geophysical Research: Solid Earth |volume=121 |number=8 |doi=10.1002/2016JB013098 |pages=6109–6131 |year=2016|bibcode=2016JGRB..121.6109A |doi-access=free }}</ref> Specifically:
* a semiannual component is added to the traditional annual periodic model;
* smooth parametric fits are to model post-seismic deformation as opposed to the traditional approach using piecewise linear functions.
|-
!ITRF2020
|2015.0
|9988
9989
9990
|<ref>{{Cite web |title=ITRF {{!}} Itrf2020 |url=https://itrf.ign.fr/en/solutions/ITRF2020 |access-date=2022-06-18 |website=itrf.ign.fr}}</ref>
|}

== Users ==
GNSS systems:<ref name=gtrf/>
* [[Galileo (satellite 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 WGS 84 before), 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/>

National systems:
* United States: WGS 84 (see above); domestic use is mainly based on [[NAD 83]] instead.
* China: CTRF 2000 per above.

<!-- This needs further rewrite. Obviously. -->
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]]
* [[Earth orientation parameters]]
* [[Geodetic datum]]
* [[International Celestial Reference System and its realizations]]
* [[Terrestrial reference frame]]
* [[World Geodetic System]]

==References==
{{Reflist}}

== 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]]