Introduction to Geodesy

Mohammad Soyeb Alam

Assistant Professor
Department of Mining Engineering
IIT(ISM), Dhanbad, India
1.0 Definition of geodesy
• According to the classical definition of Friedrich Robert Helmert (1880),
“geodesy is the science of the measurement and mapping of the Earth’s
surface.”
• Helmert’s definition is fundament to geodesy even today.
• The surface of the earth, to a large extent, is shaped by the earth’s gravity, and
most geodetic observations are referenced to the earth's gravity field.
• The above definition of geodesy, includes the determination of the earth’s
external gravity field.
• Since ancient times, the reference system for the survey of the earth has been
provided by extraterrestrial sources (Stars). This demands the earth’s orientation
in space to be implied into the focus of geodesy.
• In recent time, the objective of geodesy has expanded to include applications in
ocean and space research.
• Geodesy, in collaboration with other sciences, is also now involved in the
determination of the surfaces and gravity fields of the other celestial bodies, such
as the moon (lunar geodesy) and planets (planetary geodesy).
• Finally the classical definition has to be extended to include temporal variations
of the earth’s figure, its orientation and its gravity field.
• With this extended definition, geodesy is part of the geosciences and engineering
sciences, including navigation and geomatics.
 2.0 Division of geodesy
1. Global geodesy includes the
determination of the shape and
size of the earth, its orientation in

Geodesy may be divided into three areas

space, and its external gravity
field.
2. Geodetic survey deals with the
Global geodesy
determination of the earth’s
surface and gravity field over a
region that typically spans a
country or a group of countries. Geodetic survey
The earth’s curvature and gravity
(national and supernational)
field must be considered in
geodetic surveys.
3. In plane surveying (topographic
surveying, cadastral surveying, Plane surveying
engineering surveying), the
details of the earth’s surface are
determined on a local level, and
thus curvature and gravity effects
are most often ignored.
3.0 Relationship between global geodesy, geodetic
surveying, and plane surveying

There is a close relationship between these three:

• Geodetic surveys are linked to reference frames (networks) established
by global geodesy, and they adopt the parameters for the figure of the
earth and its gravity field. On the other hand, the results of geodetic
surveys contribute to global geodesy.
• Plane surveys, in turn, are generally referenced to control points
established by geodetic surveys. They are used extensively in the
development of national and state map series, cadastral and geo-
information systems, and in civil engineering projects.
• The measurement and data evaluation methods applied in national
geodetic surveys nowadays mostly are similar to those used in global
geodetic work. In particular, space methods (satellite geodesy) which
have long been a dominant technique in global geodesy, are now also
commonly employed in regional and local surveys. This also requires a
more detailed knowledge of the gravity field at regional and local scales.
4.0 Objective of geodesy

Based on the concept of geodesy defined in previous slides, the objective of geodesy
with respect to planet Earth may be described as follows:
“The objective of geodesy is to determine the figure and external
gravity field of the Earth, as well as its orientation in space, as a
function of time, from measurements on and exterior to the Earth’s
surface.”
• This geodetic boundary-value problem incorporates a geometric (figure of the earth)
and a physical (gravity field) part; both are closely related.
Figure of the Earth:
• By the figure of the Earth we mean the physical and the mathematical surface of the
Earth as well as a geodetic reference model (e.g., Moriz, 1990)
• The physical surface of the Earth is the border between the solid or fluid masses and
the atmosphere. The ocean floor may be included in this definition, being the
bounding surface between the solid terrestrial body and the oceanic water masses.
• The irregular surface of the solid Earth (continental and ocean floor topography)
cannot be represented by a simple mathematical (analytical) function.
• Continental topography is therefore described point wise by coordinates of control
(reference) points. Given as adequate dense control points, the detailed structure of
this surface can be determined by interpolation of data from spatial and terrestrial
topographic and photogrammetric surveying and from hydrographic surveys.
Objective of geodesy (continued)
• On the other hand, the ocean surface (70% of the Earth’s surface) is easier to
represent.
• If we neglect the effects of ocean currents and other “disturbances” like ocean
tides, it forms a part of a level or equipotential surface of the Earth’s gravity field
(surface of constant gravity potential).
• We may think of this surface as being extended under the continents and identify
it as the mathematical figure of the Earth, which can be described by a condition
of equilibrium (Helmert, 1880/1884).
• J.B. listing (1873) designated this level surface as geoid.
External gravity field:
• The description of the external gravity field including the geoid represents the
physical aspect of the problem of geodesy
• In solving this problem, the Earth’s surface and the geoid are considered as
bounding surfaces in the Earth’s gravity field.
• Based on the law of gravitation and the centrifugal force and the centrifugal force
(due to Earth’s rotation), the external gravity field of the Earth can be modelled
analytically and described by a large number of model parameters. A geometric
description is given by the infinite number of level surfaces extending completely
or partially exterior to the Earth’s surface. The geoid as a physically defined
Earth’s figure plays a special role in this respect.
Objective of geodesy (continued)

Orientation of the Earth in space:

• Reference systems are introduced in order to describe the orientation of the Earth
in space (celestial reference system) as well as its surface geometry and gravity
field (terrestrial reference system).
• The definition and realization of these systems has become a major part of global
geodesy; the use of three dimensional Cartesian coordinates in Euclidean space is
adequate in this context. However, due to the demands of the users, reference
surfaces are introduced. We distinguish between curvilinear surface coordinates
for horizontal positioning, and heights above some zero height surface for
vertical positioning. Because of its simple mathematical structure, a rotational
ellipsoid, flattened at the poles, is well suited for describing horizontal positions,
and consequently it is used as a reference surface in geodetic surveying. In plane
surveying, the horizontal plane is generally a sufficient reference surface.
Because of the physical meaning of the geoid, this equipotential surface is well
suited as a reference for heights.
• For many applications, a geodetic reference Earth (Earth model, normal Earth) is
needed. It is realized through a mean Earth ellipsoid that optimally approximates
the geometry (geoid) and the gravity field of the Earth. Figure 1 shows the
mutual location of the surfaces to be determined in geodesy.
Objective of geodesy (continued)

Figure 1: Physical surface of the Earth, geoid, and ellipsoid

Objective of geodesy (continued)

Temporal variations:
• The body of the Earth, its gravity field and its orientation are subject to temporal
variations of secular, periodic, and episodic nature; these changes can occur
globally, regionally, and locally.
• Geodetic measurement and evaluation techniques are now able to detect partly
these variations to high level of accuracy. Accordingly, geodetic observations and
derived parameters must be considered as time-dependent quantities. If time-
dependent results are required, the observations must be corrected for temporal
variations, and the final results have to be referred to a specified epoch. On the
other hand, by determining temporal variations, geodesy contributes to the
investigation of the kinematics and dynamics of the Earth.
5.0 Historical development of geodesy
• The formulation of the object of geodesy described in previous slides did not
fully matured till the nineteenth century. However, the question of the figure of
the Earth was contemplated already in antiquity.
• In fact geodesy, together with astronomy and geography are among the oldest
sciences dealing with the planet Earth.
• Superseding the use of the sphere as a model for the Earth, the oblate rotational
ellipsoid became widely accepted as the model of choice in the first half of the
eighteenth century.
• The significance of the gravity field was also recognized in the nineteenth
century, leading to the introduction of geoid.
• In the second half of the twentieth century, satellite techniques permitted the
realization of the three dimensional concept of geodesy.
• At the same time, a drastic increase in the accuracy of geodetic observations
required that time variations be taken into account. This led to the concept of four
dimensional geodesy.
References for the historical development of geodesy:
Todhunter (1873), Perrier (1939), Fischer (1975), Bialas (1982), and Smith (1986).
5.0 Historical development of geodesy (continued)

5.1 The spherical Earth model

• Various opinions about the figure of the Earth prevailed in the past, e.g., the
notion of an Earth disk encircled by oceans (Homer’s lliad around 800 B.C.,
Thales of Milet about 600 B.C.). Considering the sphere aesthetically appealing,
Pythagoras (around 580-500 B.C.) and his school proposed a spherical shaped
Earth. By the time of Aristotle (384-322 B.C.), the spherical concept was
generally accepted and even substantiated by observations. For example,
observers noted the round shadow of the Earth in lunar eclipses and the apparent
rising of an approaching ship at the horizon. In china the spherical shape of the
Earth was also recognized in the First century A.D.
• Eratosthenes of Alexandria (276-195 B.C.) was the first who, based on the
assumption of a spherical Earth, deduced the earth’s radius from measurements
(Schwarz, 1975; Lelgemann, 2010); he is often regarded as the founder of the
geodesy. The principle of the arc-measurement method developed by him was
applied till modern times: from geodetic measurements, the length ΔG of a
meridian arc (or any other great circle) is determined; astronomical observations
furnish the associated central angle ψ (Fig. 2). The radius of Earth is then given
by
ΔG
ψ.
 5.1 The spherical Earth model

• Eratosthenes found that the rays of sun descended vertically

into a well in Syne (modern day Assuan), at the time of summer
solstice. whereas in Alexandria (approximately on the same
meridian as Syene), the sun’s rays formed an angle with the
direction of the plumb line. from the length of the shadow of a
vertical staff produced in a hemispherical shell, Eratosthenes
determined this angle as 1/50 of a complete circle, i.e., 7º12’ .
Further, from Egyptian cadastre maps, which were based on the
information of “bematists” (step counters), Eratosthenes,
probably estimated the distance from the Syene to Alexandria to
be 5000 stadia. with the length of the Eratosthenes stadium
assumed as 158.7 m (Egyptian norms), the Earth radius is
computed to be about 6300 km, which is close to the real value
of 6370 km. Another ancient determination of the Earth’s radius
is attributed to Posidonius (135-51 B.C.). Using the
(approximate) meridian arc from Alexandria to Rhodes, He Fig. 2 Arc measurement
observed the star Canopus to be on the horizon at Rhodes, while of Eratosthenes
at a culmination height of 7º30’ at Alexandria, this again
corresponds to the central angle between two sites. Klaudios
Ptolemaios (around 100-160 A.D.) finally established the
geocentric world system of Aristotle by fundamental
publications on astronomy. These works included star catalogs,
maps and lists with geographical coordinates of many places;
they dominated the view of the world until the beginning of
modern times (e.g. Kleinberg et al., 2011).
 5.1 The spherical Earth model
• During the middle ages in Europe, the question of the figure of the Earth was not
pursued further, although the knowledge of the Earth’s spherical shape was not lost
and especially kept in the monasteries. Documentation from China shows that an
astronomic-geodetic survey between 17º and 40º latitude was carried out by the
astronomers Nankung Yueh and I-Hsing c. 725 A.D. in order to determine the length
of a meridian. A meridian arc of 2º extension was measured directly with ropes by the
Arabs (c. 827 A.D.) northwest of Bagdad, during the caliphate of Al-Mamun. At the
beginning of the modern age, the French physician J. Fernel (1525) described an
arc measurement between Paris and Amiens, at which the geographical latitudes were
determined using a quadrant, and the length of the arc was computed from the number
of rotations of wagon wheel.
• Later arc measurement based on the spherical Earth model benefited from
fundamental advances in instrumentation technology, especially by the invention of
the telescope in the Netherlands (c. 1600), and its modification and application in
astronomy by Galilei and Kepler (1610/1611). Equally important was in the
progress in methodology by the development of the triangulation. With this method,
the hitherto tedious and inaccurate direct length measurement or even estimation of a
spherical arc was replaced by an indirect procedure. The angles in a chain of
triangles following the arc (triangulation network) were observed with an angle
measuring devices of high precision (the quadrant and later the theodolite), and
the scale of the network was derived from one (or more) short baselines measured
with high precision. With proper reduction of the observations to the meridian, the
length of the arc then is provided by trigonometric formulae. After the initial
application of triangulation by Gemma Frisius (1508-1555) in the Netherlands,
and by Tycho Brahe (1546-1601) in Denmar, the Dutchman Willebrord Snell van
Royen, called Snellius (1580-1626), conducted a first triangulation (1614/15) in
order to determine the radius of the Earth from the meridian arc between Bergen op
Zoom and Alkmaar (Holland), (Haasbroek, 1968)
 5.1 The spherical Earth model
• Although triangulation combined with astronomic positioning soon proved as
an economic and accurate method of arc measurement, other strategies for
determining the earth radius were also pursued. A. Norwwod, for example, still
employed a direct length measurement using a chain when determining the
meridian arc between London and York (1633-1635). The method of reciprocal
zenith angles is another technique that has been used to determine the central
angle between points on a meridian arc. Already proposed by Kepler (1607), the
Italian priests F. Grimaldi and G.B. Riccioli used this method in 1645, between
Bolonga and Modena (Fig 3) the central angle may be computed from the zenith
angles and observed at locations and according to
Ψ

This procedure makes an arc measurement independent of astronomic observations,

but it does not yield satisfactory results due to the inaccurate determination of the
curvature of light rays (refraction anomalies) affecting the observed zenith angles.
 5.1 The spherical Earth model (continued)

• Through the initiative of the French Academy of Sciences (founded in Paris,

1966), France assumed the leading role in geodesy in the seventeenth and
eighteenth centuries. In 1669/70 the French abbot J. Picard measured the
meridian arc through Paris between Malvoisine and Amiens with the aid of a
triangulation network; he was the first to use a telescope with cross hairs as part
of the quadrant employed for the measurement of the angles. The value Picard
obtained for the radius of the Earth (deviation from the exact value +0.01%)
aided Newton in the verification of the law of gravitation, which he had
formulated already in 1665/66

5.2 The ellipsoidal Earth model

• In the sixteenth and the seventeenth centuries, new observations and ideas from
astronomy and physics decisively influenced the perception of the figure of the
earth and its position in space. Nicolaus Copernicus (1473-1543) achieved the
transition from the geocentric universe of Aristotle and Ptolemy to a heliocentric
system (1543), which Aristarchos of Samos (about 310-250 B.C.) had already
postulated. Johannes Kepler (1571-1630) discovered the laws of planetary
motion (1609: “Astronomia nova…” , 1619: “Harmonices mundi”) , in which
the planets followed elliptical orbits in a systematic manner. Finally Galileo
Galilei (1564-1642) established the fundamentals for mechanical dynamics (law
 of falling bodies and law of pendulum motion), and strengthened the idea of
heliocentric world system by a multitude of astronomic observations of high
accuracy. Being a strong advocate of the new system, he decisively contributed to
its final success, notwithstanding the long-lasting opposition of the Catholic
Church.
• In 1666, the astronomer J.D. Cassini observed the flattening of the poles of Jupiter.
On an expedition to Cayenne to determine martian parallaxes (1672/73), the
astronomer J. Richer discovered that a one-second pendulum regulated in Paris
needed to be shortened in order to regain oscillations of one second. From this
observation, and on the basis of the law of pendulum motion, one can infer an
increase in gravity from the equator to the poles. This effect was confirmed by by the
English astronomer E. Halley when comparing pendulum measurements in St. Helena
to those taken in London (1677/78).
• Founded on these observations and his theoretical work on gravitation and
hydrostatics, Issac Newton (1643-1727) developed an Earth model based on physical
principles, and presented it in his famous “Philosophiae Naturalis Principia
Mathematica” (1687). Based on the law of gravitation, newton proposed a rotational
ellipsoid as an equilibrium figure for a homogeneous, fluid, rotating Earth. The
flattening
f=
(with semi-major axis a and semi-minor axis b of the ellipsoid) of Newton’s ellipsoid
was 1/230. He also postulated an increase in gravity acceleration from the equator to the
poles proportional to sin2 𝜑 (geographical latitude 𝜑). At the same time, the Dutch
Physicist Christian Huygens (1629-1695), after having developed the principle of the
pendulum clock and the law of central motin, also calculated an Earth model flattened at
the poles. Shifting the source of the Earth’s attractive forces to the center of the Earth, he
obtained a rotationally-symmetric equilibrium surface with a meridian curve of fourth
order and flattening of 1/576
5.3 The geoid, arc measurements and national geodetic surveys
• Arc measurements at various latitudes were now required to verify the proposed
ellipsoidal Earth models. Theoretically, the length of a 10 arc (meridian arc for a
difference of 10 in latitude), in the case of flattened poles, should increase pole-
ward from the equator. the ellipsoidal parameters a,b or a,f then can be computed
from two arc measurements (see fig. 4).

Fig. 4 : Latitude arc measurement

5.3 The geoid, arc measurement and national geodetic surveys
• As recognized by P.S. Laplace (1802), C.F. Gauss (1828), F.W. Bessel (1837),
and others, the assumption of an ellipsoidal-Earth model is no longer tenable at a
high level of accuracy. The deviation of the physical plumb line, to which the
measurements refer, from the ellipsoidal normal can no longer be ignored. This
deviation is known as the deflection of the vertical. While adjusting several arc
measurements for the determination of the ellipsoidal parameters, contradictions
were found which greatly exceeded the observational accuracy.
• This led to the refined definition of the “figure of the Earth” by Gauss and
Bessel, who clearly distinguished between the physical surface of the Earth,
geoid as the mathematical surface, and the ellipsoid as a reference surface
approximating it. With the definition of geodesy, F .R. Helmert made the
transition to the actual concept of the figure of the Earth (Moritz, 1990).
5.4 Three-dimensional geodesy
• The three-dimensional concept of geodesy consists of the common treatment of
horizontal and vertical positioning within the same mathematical model. This
was suggested already by Bruns (1878), who proposed to determine the surface
of the Earth point wise using a spatial polyhedron together with all exterior
level surfaces. However, three-dimensional computations were not carried out in
practice due to the problems associated with the inclusion of height
measurements into the model. Trigonometrically derived height differences over
large distances suffered from refraction anomalies, and geometric levelling could
not be reduced to the ellipsoid as accurate geoid heights above the ellipsoid were
not available.
• The concept of three-dimensional geodesy was revived by Marussi (1949) and
Hotine (1969), while in 1945 Molodensky demonstrated that the physical surface
of the Earth and its external gravity field can be determined from surface
measurements only, without needing the geoid (Molodensky, 1958)
• Vaisala (1946) introduced Steller triangulation from high altitude balloons as a
first step to realize the three-dimensional concept.
• This technique was followed by electromagnetic distance measurements in 1950s
and 1960s, using both terrestrial and airborne methods.
• Satellite geodesy provided a technological breakthrough after the launch of the
Russian satellite Sputnik I in 1957.
5.4 Three-dimensional geodesy (continued)
• Observations to orbiting satellites were used to establish control points in a three-
dimensional system, and provided global gravity field information.
• Beginning in the 1980s, the NAVSTAR Global Positioning System (GPS) today
dominates geodetic measuring techniques. Since the 1990’s global geodetic
networks have been built up by different space techniques, and are regularily
maintained by international services.
• Among the practical problems which geodesy is facing today is the connection of
classical horizontal and vertical control networks to the global system, and their
transformation into three-dimensional nets. This includes the determination of
the geoid with respect to a global reference ellipsoid, with high accuracy and
spatial resolution.
• Recently, kinematic methods have gained great importance, especially with the
extensive use of GNSS like GPS. The measuring systems are carried on moving
platforms (e.g., satellite, airplane, ship, car) and provide data referring to the
geodetic reference system by continuous positioning (navigation).
5.5 Four-dimensional geodesy
• The beginning of four-dimensional geodesy (Mather, 1973) may be reckoned from the
detection of polar motion by F. Kustner (1884/85) and the first observations of the Earth
tides by E.v. Rebeur-Paschwitz (1889-1893), at the Geodetic Institute Potsdam.
• Monitoring of crustal deformations related to seismic activities began in Japan and the
U.S.A about 100 years ago. Interest in these phenomena was motivated by disastrous
seismic events, such as the San Francisco Earthquake of 1906.
• In Fennoscandia, precise leveling and tide gauge registrations started in the 1880s and were
used to determine the regions’s large-scale vertical uplift caused by postglacial rebound.
• Today, the variations of the Earth’s rotation and the movements of the tectonic plates are
regularly observed through global networks. In addition, a number of regional control
networks has been set up, especially at tectonic plate boundaries. Gravity field variations
with time are derived from the analysis of satellite orbits and from dedicated satellite
gravity missions (global and regional scale), as well as from terrestrial gravity
measurements (local scale). The Earth’s tide have also been modeled successfully using
terrestrial and satellite methods.
• Worldwide, large efforts are nowadays made to measure and analyse all types of
geodynamic phenomena, with geodetic methods playing a significant role, e.g. NASA
(1983), Lambeck (1988), Herring (2009). With a further increase in accuracy of geodetic
observations and a better resolution in space and time, geodesy now more than ever
contributes to the understanding of the Earth system dynamics and global change
processes. A long-term enterprise directed to this objective is the Global Geodetic
Observing System (GGOS) of the International Association of Geodesy. The time-
variability of geodetic products (geometric and gravimetric networks, gravity field, Earth’s
orientation) also increasingly forces geodetic practice to take temporal changes into
account, and to present geodetic products accordingly.
6.0 Organization of geodesy and literature
6.1 National organization
• The problems of global geodesy may be solved only by international cooperation of
research institutions and national agencies, within the framework of international
organization and services
• University institutes and departments pursue fundamental and applied research in the
fields of geodesy and remote sensing, geophysics, astronomy and space sciences,
geomatics and surveying engineering. Worldwide, there is a multitude of
corresponding institutions engaged in this research, which can not be listed here
explicitly (see Geodesist’s Handbook 2004, J. Geod. 77, No. 10-11).
• In several countries, academy or governmental institutes are also engaged in geodetic
research.
e.g.
 Austria – Institute of Space Research, Academy of Sciences, Graz
 China – Institute of Geodesy And Geophysics, Wuhan
 Czech Republic- Research Institute of Geodesy, Topography And Cartography
 Finland – Finnish Geodetic Institute
 Germany- DGFI, Munchen and GFZ, Potsdam
 Japan- National Research Institute for Earth Sciences and Disaster Prevention
 Poland – Institute of Geodesy and Cartography, Space Research Center, Warsaw
 Russia- Institute of Physics of Earth, Moscow
Organization of geodesy and literature (continued)
• Further, The national geodetic surveys are carried out according to the guidelines
of the national survey authority, organized either as a central agency or in
decentralized institutions.
e.g.
 India – Survey of India
 For other country - you may refer introduction chapter of ‘Geodesy’ authored by
Wolfgang
• In addition to these, a number of non-geodetic institutions, in course of their
special tasks and projects, are also concerned with geodetic problems. These
groups develop theories, measuring systems and methods, and in particular are
involved with the collection and evaluation of geodetic data.
e.g.
 Space agencies – ASI, DLR, NASA etc.
 For more informations - you may refer introduction chapter of ‘Geodesy’
authored by Wolfgang
Organization of geodesy and literature (continued)
6.2 International collaboration
• At the beginning of arc measurement in the Kingdom of Hannover (1821), C.F. Gauss
had already expressed his desire for international collaboration. According to Gauss,
this geodetic network would be connected to neighboring triangulation networks,
aiming toward an eventual merger of the European observatories. organized
international collaboration originated with the memorandum by the Prussian general
J.J. Baeyer (1794-1885). In 1862, the “Mitteleuropaische Gradmessung” was founded
in Berlin and was being among the first international scientific associations of
significance; Baeyer became its first president. After expanding to the “Europaische
Gradmessung” (1867), and to the Internationale Erdmessung” (‘Association
Geodesique Internationale,”1886), the association engaged in fruitful activity, which
was especially inspired by the works of Helmert as director of the Central Bureau.
• After the dissolution of the “Internationale Erdmessung” during the first World war,
the “International Union of Geodesy and Geophysics” (IUGG) was founded in 1919.
in 2011, this organization had a membership 65 countries. It consists of one geodetic
and seven geophysical associations, dealing with the cryosphere, with geomagnetism ,
hydrology, meteorology, oceanography, seismology, and volcanology.
• The “International Association of Geodesy” (IAG) is led by a president who is elected
every four years, and who is assisted by a Vice President and a General Secretary,
together they form the IAG Bureau. The executive committee coordinates the IAG’s
work and formulates the general policy, while the council (delegates from the
membership countries) is responsible for governance, strategic policy and direction.
The IUGG and IAG meet at General Assemblies at four year intervals. In addition,
numerous symposia and scientific conferences are organized to treat special themes;
among these area the IAG Scientific assemblies, which are held between the General
Assemblies.
Organization of geodesy and literature (continued)
6.2 International collaboration (continued)
• The scientific work of the IAG is performed, by the commissions, Services, inter
commission committees, the communication and outreach branch, and IAG projects.
Currently there are four commissions established for long term problems (Reference
Frames, Gravity Field, Earth Rotation and Geodynamics, Positioning and Application),
which may set up Study Groups or Working Groups for topics of limited scope. A focal
point for theoretical geodesy is the inter-commission committee on Theory. The “Global
Geodetic Observing System (GGOS)” was established in 2003, as an integral IAG
component along with Services and Commissions. It “works with other IAG components to
provide the geodetic infrastructure necessary for monitoring the Earth system and global
change research”
• An important part of the IAG work is done by Services, through collecting and analyzing
observations in order to generate products relevant to geodesy and other sciences and
applications.
• Currently the following Services partly maintained in collaboration with other scientific
organizations:
 International GNSS Service (IGS) with Central Bureau at the NASA JPL, Pasadena,
California
 International VLBI Service for Geodesy and Astronomy (IVS)
 International Laser Ranging Service (ILRS)
 International Gravimetric Bureau (BGI), Toulouse, France
 International Geoid Service (IGeS), Milano
Organization of geodesy and literature (continued)
6.2 International collaboration (continued)

International Centre for Earth Tides (ICET), France

International Earth Rotation and Reference Systems Service (IERS) with
the Central Bureau at the BKG, Frankfurt, a.M.
International DORIS Service, France
International Gravity Field Service with the Central Bureau at the
National Geospatial-Intelligence Agency NGA, USA
International Centre for Global Earth Models, GFZ Potsdam
International Digital Elevation Model Service, U.K
Permanent Service for Mean Sea Level, Proudmsn Oceanographic
Laboratory, Liverpool, U.K
Bureau International des Poids et Mesures-Time, Frequency and
Gravimetry Section, Sevres, France
International Altimetry Service IAS
IAG Bibliographic Service, Leipzig, Germany
Organization of geodesy and literature (continued)
6.3 Literature
• References to textbooks and Journals for geodesy and related fields
(mathematics, physics, astronomy, geophysics, surveying engineering, mapping
and geomatics): (refer book ‘Geodesy’ authored by Wolfgang).
• A list of geodetic and geodetically relevant publication series is given in Journal
of Geodesy 77(2004): 742-748, and revised version is available at IAG Website
http://www.iag-aig.org.
• Journal of Geodesy is the official journal of the IAG.
• The results of each general Assembly of the IAG are complied in the Travaux
(proceedings).
• National reports are collected and store at the Central Bureau of the IAG.
• The proceedings of IAG symposia are published in a separate series (Springer)
• Among the recent scientific technical journals in the field of geodesy,
geophysics, navigation, and surveying (you may refer introduction chapter of
‘Geodesy’ authored by Wolfgang)
• Technical reports issued by university and research institutes, as well as by some
governmental agencies (you may refer introduction chapter of ‘Geodesy’
authored by Wolfgang)