Geodesy: Difference between revisions
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[[File:GPS antenna and receiver Mount Blue Sky Colorado 23 August 2023.png|thumb|upright=1.05|A modern instrument for geodetic [[measurements]] using [[GNSS|satellites]]]] | [[File:GPS antenna and receiver Mount Blue Sky Colorado 23 August 2023.png|thumb|upright=1.05|A modern instrument for geodetic [[measurements]] using [[GNSS|satellites]]]] | ||
'''Geodesy''' or '''geodetics'''<ref>{{Cite book |title=[[Cambridge English Dictionary]] |chapter=geodetics |access-date=2024-06-08 |chapter-url=https://dictionary.cambridge.org/us/dictionary/english/geodetics}}</ref> is the [[science]] of measuring and representing the [[Figure of the Earth|geometry]], [[Gravity of Earth|gravity]], and [[Earth's rotation|spatial orientation]] of the [[Earth]] in [[Relative change|temporally varying]] [[ | '''Geodesy''' ({{IPAc-en|dʒ|iː|ˈ|ɒ|d|ɪ|s|i}}, {{respell|jee|OD|iss|ee}}) or '''geodetics'''<ref>{{Cite book |title=[[Cambridge English Dictionary]] |chapter=geodetics |access-date=2024-06-08 |chapter-url=https://dictionary.cambridge.org/us/dictionary/english/geodetics}}</ref> is the [[science]] of measuring and representing the [[Figure of the Earth|geometry]], [[Gravity of Earth|gravity]], and [[Earth's rotation|spatial orientation]] of the [[Earth]] in [[Relative change|temporally varying]] [[three-dimensional space|3D space]]. It is called [[planetary geodesy]] when studying other [[astronomical body|astronomical bodies]], such as [[planet]]s or [[Natural satellite|circumplanetary system]]s.<ref name="VK">{{Cite book |url=https://shop.elsevier.com/books/geodesy/vanicek/978-0-444-87775-8 |title=Geodesy: The Concepts |date=November 1, 1986 |publisher=[[Elsevier]] |isbn=978-0-444-87775-8 |editor-last=Vaníček |editor-first=Petr |editor-link=Petr Vaníček |edition=Second |pages=45–51 |chapter=Structure of Geodesy |doi=10.1016/B978-0-444-87775-8.50009-5 |quote=...{{nbsp}}geodesy was thought to occupy the space delimited by the following definition ... "the science of measuring and portraying the earth's surface." ... the new definition of geodesy ... "the discipline that deals with the measurement and representation of the earth, including its gravity field, in a three-dimensional time varying space." ... a virtually identical definition ... the inclusion of other celestial bodies and their respective gravity fields. |editor2-last=Krakiwsky |editor2-first=Edward J.}}</ref> Geodetic job titles include '''geodesist''' and '''geodetic surveyor'''.<ref>{{cite web | website=Occupational Information Network |title=Geodetic Surveyors | date=2020-11-26 | url=https://www.onetonline.org/link/summary/17-1022.01 | access-date=2022-01-28}}</ref> | ||
[[ | Through highly accurate [[observations]], geodesy provides the [[Natural sciences|scientific basis]] for [[Mapping (cartography)|mapping]], [[navigation]], and [[Geopositioning|positioning]], and supports applications such as [[infrastructure|infrastructure development]] (including [[construction]]), [[natural resources|natural resource management]], [[mineral exploration]], and [[geophysics]]. Its measurements underpin modern [[geospatial]] [[reference frames]] used in [[transportation]], [[satellite]] systems, global [[trade]], and [[Synchronization in telecommunications|timekeeping]]. | ||
Geodetic | [[Geodynamics|Geodynamic]] phenomena, including [[crust (geology)|crustal]] motion, [[tide]]s, and [[polar motion]], are studied through global and national [[Geodetic control network|control networks]], [[space geodesy]] and terrestrial geodetic techniques, and the use of [[Geodetic datum|datums]] and [[coordinate system]]s. | ||
== History == | == History == | ||
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== Definition == | == Definition == | ||
Geodesy refers to the science of measuring and representing [[geospatial information]], while [[geomatics]] encompasses practical applications of geodesy on local and regional scales, including [[surveying]]. | |||
Geodesy originated as the science of measuring and understanding Earth's geometric shape, orientation in space, and gravitational field; it is now also applied to other [[Astronomical object|astronomical bodies]] in the [[Solar System]].<ref name=VK/> | |||
To a large extent, Earth's shape is the result of [[Earth's rotation|rotation]], which causes its [[equatorial bulge]], and the competition of geological processes such as the [[Continental collision|collision of plates]], as well as of [[Volcano|volcanism]], resisted by Earth's gravitational field. This applies to the solid surface, the liquid surface ([[dynamic sea surface topography]]), and [[Earth's atmosphere]]. For this reason, the study of Earth's gravitational field is called [[physical geodesy]]. | To a large extent, Earth's shape is the result of [[Earth's rotation|rotation]], which causes its [[equatorial bulge]], and the competition of geological processes such as the [[Continental collision|collision of plates]], as well as of [[Volcano|volcanism]], resisted by Earth's gravitational field. This applies to the solid surface, the liquid surface ([[dynamic sea surface topography]]), and [[Earth's atmosphere]]. For this reason, the study of Earth's gravitational field is called [[physical geodesy]]. | ||
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{{main|Geoid|Reference ellipsoid}} | {{main|Geoid|Reference ellipsoid}} | ||
{{unreferenced section|date=February 2024}} | {{unreferenced section|date=February 2024}} | ||
[[File:Geoid undulation 10k scale.jpg | [[File:Geoid undulation 10k scale.jpg|thumb|[[Geoid]], an approximation for the shape of the [[Earth]]; shown here with [[vertical exaggeration]] (10000 vertical scaling factor).]] | ||
[[File:Surface of latitude ellipsoid cone.gif | [[File:Surface of latitude ellipsoid cone.gif|thumb|[[Ellipsoid]] - a mathematical representation of the [[Earth]]. When mapping in geodetic coordinates, a latitude circle forms a truncated cone.]] | ||
[[File:WGS84_mean_Earth_radius.svg|thumb|upright=1.0|Equatorial ({{mvar|a}}), polar ({{mvar|b}}) and mean Earth radii as defined in the 1984 [[World Geodetic System]]]] | [[File:WGS84_mean_Earth_radius.svg|thumb|upright=1.0|Equatorial ({{mvar|a}}), polar ({{mvar|b}}) and mean Earth radii as defined in the 1984 [[World Geodetic System]]]] | ||
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{{further|World Geodetic System}} | {{further|World Geodetic System}} | ||
{{unreferenced section|date=February 2024}} | {{unreferenced section|date=February 2024}} | ||
[[File:Datum Shift Between NAD27 and NAD83.png | [[File:Datum Shift Between NAD27 and NAD83.png|thumb|Datum shift between [[NAD27]] and [[NAD83]], in metres]] | ||
The locations of points in 3D space most conveniently are described by three [[cartesian coordinate system|cartesian]] or rectangular coordinates, ''X'', ''Y'', and ''Z''. Since the advent of satellite positioning, such coordinate systems are typically [[geocentric]], with the Z-axis aligned to Earth's (conventional or instantaneous) rotation axis. | The locations of points in 3D space most conveniently are described by three [[cartesian coordinate system|cartesian]] or rectangular coordinates, ''X'', ''Y'', and ''Z''. Since the advent of satellite positioning, such coordinate systems are typically [[geocentric]], with the Z-axis aligned to Earth's (conventional or instantaneous) rotation axis. | ||
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=== Coordinate systems in the plane === | === Coordinate systems in the plane === | ||
{{main|Horizontal position}} | {{main|Horizontal position}} | ||
[[File:Elliptical coordinates grid.svg | [[File:Elliptical coordinates grid.svg|thumb|2D grid for elliptical coordinates]] | ||
[[File:Litography archive of the Bayerisches Vermessungsamt.jpg | [[File:Litography archive of the Bayerisches Vermessungsamt.jpg|thumb|A [[Munich]] archive with [[lithography]] plates of maps of [[Bavaria]]]] | ||
In geodetic applications like [[surveying]] and [[map]]ping, two general types of coordinate systems in the plane are in use: | In geodetic applications like [[surveying]] and [[map]]ping, two general types of coordinate systems in the plane are in use: | ||
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== Heights == | == Heights == | ||
{{further|Vertical position|Vertical datum}} | {{further|Vertical position|Vertical datum}} | ||
[[File:An-illustration-of-height-measurement-using-satellite-altimetry.jpg | [[File:An-illustration-of-height-measurement-using-satellite-altimetry.jpg|thumb|Height measurement using satellite altimetry]] | ||
In geodesy, point or terrain ''[[height]]s'' are "[[above sea level]]" as an irregular, physically defined surface. | In geodesy, point or terrain ''[[height]]s'' are "[[above sea level]]" as an irregular, physically defined surface. | ||
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{{see also|Geodetic network#Measurement techniques}} | {{see also|Geodetic network#Measurement techniques}} | ||
{{unreferenced section|date=February 2024}} | {{unreferenced section|date=February 2024}} | ||
[[File:GPS satellite approaching 23 years on orbit (1060259).jpeg | [[File:GPS satellite approaching 23 years on orbit (1060259).jpeg|thumb|[[GPS]] Block IIA satellite orbits over the [[Earth]].]] | ||
[[File:Geodetic Control Mark.jpg | [[File:Geodetic Control Mark.jpg|thumb|Geodetic control mark]] | ||
[[File:Apollo IMU at Draper Hack the Moon exhibit.agr.jpg | [[File:Apollo IMU at Draper Hack the Moon exhibit.agr.jpg|thumb|[[Inertial navigation|Navigation]] device, [[Apollo program]]]] | ||
General [[geopositioning]], or simply positioning, is the determination of the location of points on Earth, by myriad techniques. '''Geodetic positioning''' employs geodetic methods to determine a set of precise geodetic coordinates of a point on land, at sea, or in space. It may be done within a coordinate system ('''point positioning''' or '''absolute positioning''') or relative to another point ('''relative positioning'''). One computes the position of a point in space from measurements linking terrestrial or extraterrestrial points of known location ("known points") with terrestrial ones of unknown location ("unknown points"). The computation may involve transformations between or among astronomical and terrestrial coordinate systems. Known points used in point positioning can be [[Global Navigation Satellite Systems|GNSS]] [[continuously operating reference station]]s or [[Triangulation (surveying)|triangulation points]] of a higher-order network. | General [[geopositioning]], or simply positioning, is the determination of the location of points on Earth, by myriad techniques. '''Geodetic positioning''' employs geodetic methods to determine a set of precise geodetic coordinates of a point on land, at sea, or in space. It may be done within a coordinate system ('''point positioning''' or '''absolute positioning''') or relative to another point ('''relative positioning'''). One computes the position of a point in space from measurements linking terrestrial or extraterrestrial points of known location ("known points") with terrestrial ones of unknown location ("unknown points"). The computation may involve transformations between or among astronomical and terrestrial coordinate systems. Known points used in point positioning can be [[Global Navigation Satellite Systems|GNSS]] [[continuously operating reference station]]s or [[Triangulation (surveying)|triangulation points]] of a higher-order network. | ||
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== Observational concepts == | == Observational concepts == | ||
[[File:AxialTiltObliquity.png | [[File:AxialTiltObliquity.png|thumb|Axial tilt (or [[Obliquity]]), rotation axis, plane of [[orbit]], [[celestial equator]] and [[ecliptic]]. [[Earth]] is shown as viewed from the [[Sun]]; the orbit direction is counter-clockwise (to the left).]] | ||
[[File:Global Gravity Anomaly Animation over OCEANS.gif | [[File:Global Gravity Anomaly Animation over OCEANS.gif|thumb|Global [[gravity anomaly]] animation over oceans from the NASA's GRACE (Gravity Recovery and Climate Experiment)]] | ||
As defined in geodesy (and also [[astronomy]]), some basic observational concepts like angles and coordinates include (most commonly from the viewpoint of a local observer): | As defined in geodesy (and also [[astronomy]]), some basic observational concepts like angles and coordinates include (most commonly from the viewpoint of a local observer): | ||
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{{further|Satellite geodesy|Geodetic astronomy|Surveying|Gravimetry|Levelling}} | {{further|Satellite geodesy|Geodetic astronomy|Surveying|Gravimetry|Levelling}} | ||
{{unreferenced section|date=February 2024}} | {{unreferenced section|date=February 2024}} | ||
[[File:GRAIL's gravity map of the moon.jpg | [[File:GRAIL's gravity map of the moon.jpg|thumb|Variations in the gravity field of the [[Moon]], from [[NASA]]]][[File:Gravity measurement devices, pendulum (left) and absolute (right) - National Museum of Nature and Science, Tokyo - DSC07808.JPG|thumb|Gravity measurement devices, pendulum (left) and absolute gravimeter (right)]] | ||
[[File:Autograv CG5 P1150838.JPG | [[File:Autograv CG5 P1150838.JPG|thumb|A relative gravimeter]] | ||
The reference surface (level) used to determine height differences and height reference systems is known as [[mean sea level]]. The traditional [[spirit level]] directly produces such (for practical purposes most useful) heights above [[sea level]]; the more economical use of GPS instruments for height determination requires precise knowledge of the figure of the [[geoid]], as GPS only gives heights above the [[GRS80]] reference ellipsoid. As geoid determination improves, one may expect that the use of GPS in height determination shall increase, too. | The reference surface (level) used to determine height differences and height reference systems is known as [[mean sea level]]. The traditional [[spirit level]] directly produces such (for practical purposes most useful) heights above [[sea level]]; the more economical use of GPS instruments for height determination requires precise knowledge of the figure of the [[geoid]], as GPS only gives heights above the [[GRS80]] reference ellipsoid. As geoid determination improves, one may expect that the use of GPS in height determination shall increase, too. | ||
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{{further|Geodetic coordinates}} | {{further|Geodetic coordinates}} | ||
{{unreferenced section|date=February 2024}} | {{unreferenced section|date=February 2024}} | ||
[[File:Latitude and longitude graticule on an ellipsoid.svg | [[File:Latitude and longitude graticule on an ellipsoid.svg|thumb|The definition of latitude (φ) and longitude (λ) on an ellipsoid of revolution (or spheroid). The graticule spacing is 10 degrees. The latitude is defined as the angle between the normal to the ellipsoid and the equatorial plane.]] | ||
Geographical [[latitude]] and [[longitude]] are stated in the units degree, minute of arc, and second of arc. They are ''angles'', not metric | Geographical [[latitude]] and [[longitude]] are stated in the units degree, minute of arc, and second of arc. They are ''angles'', not metric | ||
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== Temporal changes == | == Temporal changes == | ||
{{see also|Geoid#Temporal change}} | {{see also|Geoid#Temporal change}} | ||
[[File:Global plate motion.jpg | [[File:Global plate motion.jpg|thumb|Global plate tectonic movement using GPS]] | ||
[[File:How VLBI Works.gif | [[File:How VLBI Works.gif|thumb|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: | 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: | ||
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* 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> | * 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> | * 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 | | * 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 |article-number=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 | * 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]].]] | [[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>). | [[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 |pages=121–144 |doi=10.24425/gac.2019.126090|doi-access=free }}</ref>). | ||
Techniques for studying geodynamic phenomena on global scales include: | Techniques for studying geodynamic phenomena on global scales include: | ||
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* Satellite positioning by [[Global Positioning System|GPS]], [[GLONASS]], [[Galileo (satellite navigation)|Galileo]], and [[BeiDou]] | * Satellite positioning by [[Global Positioning System|GPS]], [[GLONASS]], [[Galileo (satellite navigation)|Galileo]], and [[BeiDou]] | ||
* [[Very-long-baseline interferometry]] (VLBI) | * [[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) | * [[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 |url=http://mediatum.ub.tum.de/node?id=1524988 }}</ref> and lunar [[laser ranging]] (LLR) | ||
* [[DORIS (satellite system)|DORIS]] | * [[DORIS (satellite system)|DORIS]] | ||
* Regionally and locally precise leveling | * Regionally and locally precise leveling | ||