Editing Geodesy (section)

== Temporal changes ==
{{see also|Geoid#Temporal change}}
[[File:Global plate motion.jpg|280px|thumb|right|Global plate tectonic movement using GPS]]
[[File:How VLBI Works.gif|280px|thumb|right|How [[very-long-baseline interferometry]] (VLBI) works]]

Various techniques are used in geodesy to study temporally changing surfaces, bodies of mass, physical fields, and dynamical systems. Points on Earth's surface change their location due to a variety of mechanisms:

* Continental plate motion, [[plate tectonics]]<ref>{{cite journal |last1=Altamimi |first1=Zuheir |last2=Métivier |first2=Laurent |last3=Rebischung |first3=Paul |last4=Rouby |first4=Hélène |last5=Collilieux |first5=Xavier |title=ITRF2014 plate motion model |journal=Geophysical Journal International |date=June 2017 |volume=209 |issue=3 |pages=1906–1912 |doi=10.1093/gji/ggx136|doi-access=free }}</ref>
* The episodic motion of tectonic origin, especially close to [[fault line]]s
* Periodic effects due to tides and tidal loading<ref>{{cite journal |last1=Sośnica |first1=Krzysztof |last2=Thaller |first2=Daniela |last3=Dach |first3=Rolf |last4=Jäggi |first4=Adrian |last5=Beutler |first5=Gerhard |title=Impact of loading displacements on SLR-derived parameters and on the consistency between GNSS and SLR results |journal=[[Journal of Geodesy]] |date=August 2013 |volume=87 |issue=8 |pages=751–769 |doi=10.1007/s00190-013-0644-1|bibcode=2013JGeod..87..751S |s2cid=56017067 |url=https://boris.unibe.ch/45844/8/190_2013_Article_644.pdf |archive-url=https://web.archive.org/web/20220318082002/https://boris.unibe.ch/45844/8/190_2013_Article_644.pdf |archive-date=2022-03-18 |url-status=live }}</ref>
* [[glaciation|Postglacial]] land uplift due to isostatic adjustment
* Mass variations due to hydrological changes, including the atmosphere, cryosphere, land hydrology, and oceans
* Sub-daily polar motion<ref>{{cite journal |last1=Zajdel |first1=Radosław |last2=Sośnica |first2=Krzysztof |last3=Bury |first3=Grzegorz |last4=Dach |first4=Rolf |last5=Prange |first5=Lars |last6=Kazmierski |first6=Kamil |title=Sub-daily polar motion from GPS, GLONASS, and Galileo |journal=Journal of Geodesy |date=January 2021 |volume=95 |issue=1 |pages=3 |doi=10.1007/s00190-020-01453-w|bibcode=2021JGeod..95....3Z |doi-access=free }}</ref>
* Length-of-day variability<ref>{{cite journal |last1=Zajdel |first1=Radosław |last2=Sośnica |first2=Krzysztof |last3=Bury |first3=Grzegorz |last4=Dach |first4=Rolf |last5=Prange |first5=Lars |title=System-specific systematic errors in earth rotation parameters derived from GPS, GLONASS, and Galileo |journal=GPS Solutions |date=July 2020 |volume=24 |issue=3 |pages=74 |doi=10.1007/s10291-020-00989-w|doi-access=free |bibcode=2020GPSS...24...74Z }}</ref>
* Earth's center-of-mass (geocenter) variations<ref>{{cite journal |last1=Zajdel |first1=Radosław |last2=Sośnica |first2=Krzysztof |last3=Bury |first3=Grzegorz |title=Geocenter coordinates derived from multi-GNSS: a look into the role of solar radiation pressure modeling |journal=GPS Solutions |date=January 2021 |volume=25 |issue=1 |pages=1 |doi=10.1007/s10291-020-01037-3|doi-access=free |bibcode=2021GPSS...25....1Z }}</ref>
* Anthropogenic movements such as reservoir construction or [[petroleum]] or water extraction

[[File:Stephen Merkowitz NASA's Space Geodesy Project.ogv|thumb|upright=1.25|A NASA project manager talks about his work for the [[Space geodesy|Space Geodesy]] Project, including an overview of its four fundamental techniques: GPS, [[very-long-baseline interferometry|VLBI]], [[Lunar laser ranging|LLR]]/[[Satellite laser ranging|SLR]], and [[DORIS (geodesy)|DORIS]].]]

[[Geodynamics]] is the discipline that studies deformations and motions of Earth's crust and its solidity as a whole. Often the study of Earth's irregular rotation is included in the above definition. Geodynamical studies require terrestrial reference frames<ref>{{cite journal |last1=Zajdel |first1=R. |last2=Sośnica |first2=K. |last3=Drożdżewski |first3=M. |last4=Bury |first4=G. |last5=Strugarek |first5=D. |title=Impact of network constraining on the terrestrial reference frame realization based on SLR observations to LAGEOS |journal=Journal of Geodesy |date=November 2019 |volume=93 |issue=11 |pages=2293–2313 |doi=10.1007/s00190-019-01307-0|bibcode=2019JGeod..93.2293Z |doi-access=free }}</ref> realized by the stations belonging to the Global Geodetic Observing System (GGOS<ref>{{cite journal |last1=Sośnica |first1=Krzysztof |last2=Bosy |first2=Jarosław |title=Global Geodetic Observing System 2015–2018 |journal=Geodesy and Cartography |date=2019 |doi=10.24425/gac.2019.126090|doi-access=free }}</ref>).

Techniques for studying geodynamic phenomena on global scales include:

* Satellite positioning by [[Global Positioning System|GPS]], [[GLONASS]], [[Galileo_(satellite_navigation)|Galileo]], and [[BeiDou]]
* [[Very-long-baseline interferometry]] (VLBI)
* [[Satellite laser ranging]] (SLR)<ref>{{cite journal |last1=Pearlman |first1=M. |last2=Arnold |first2=D. |last3=Davis |first3=M. |last4=Barlier |first4=F. |last5=Biancale |first5=R. |last6=Vasiliev |first6=V. |last7=Ciufolini |first7=I. |last8=Paolozzi |first8=A. |last9=Pavlis |first9=E. C. |last10=Sośnica |first10=K. |last11=Bloßfeld |first11=M. |title=Laser geodetic satellites: a high-accuracy scientific tool |journal=Journal of Geodesy |date=November 2019 |volume=93 |issue=11 |pages=2181–2194 |doi=10.1007/s00190-019-01228-y|bibcode=2019JGeod..93.2181P |s2cid=127408940 }}</ref> and lunar [[laser ranging]] (LLR)
* [[DORIS_(satellite_system)|DORIS]]
* Regionally and locally precise leveling
* Precise tachymeters
* Monitoring of gravity change using land, airborne, shipborne, and spaceborne [[gravimetry]]
* Satellite [[altimetry]] based on microwave and laser observations for studying the ocean surface, sea level rise, and ice cover monitoring
* [[Interferometric synthetic aperture radar]] (InSAR) using satellite images.