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A Constituent Association of the International Union of Geodesy and Permanent GPS Station in southern Greenland, WhatWhat isis Geodesy?Geodesy? part of the GNET Project (Photo: M. Bevis)

The is not composed of solid rock, but During the evolution of geodetic science, it due to the increase of temperature towards its has been discovered that the shape of the Earth centre it is built up from a mixture of viscous is not round, but it ‘bulges’ outward along the and solid materials. Thus the shape of the equator. Even this is an over simplification. Earth is oblate, because the centrifugal force The Earth has many ‘hills and troughs’ in the stemming from its rotational motion thrusts potential field, indicating significant departures from symmetric mass distribution the masses out at the . within the solid Earth. This is superimposed on the topographic variability we are all familiar What about the hills, mountain ranges, with. and deep sea trenches? Why do we need accurate ? These ‘topographic features’ are quite small compared to the size of our . Of course Recall the old saying: they are measured and drawn on maps, but “You can not tell where you are going un- in Geodesy their contribution to the shape of less you know where you have been.” the planet is quite small. Maps play an important role in our lives. These topographic features range from about We need them to find our way in the world – to 9 km above (Mount Everest) to navigate. In ancient mankind used approximately 12 km below sea level (Mariana landmarks to navigate their way to friends, to Trench). The diameter of the Earth is roughly towns and ports, or other places of interest. 12756 km. Today we often use urban landmarks, such However, as the accuracy of our observation as shopping malls, churches, skyscrapers, techniques improves, the geodetic influence of road intersections, and other points of interest. topographic features become more and more But what happens, if we are not familiar with important. For example, the gravitational the town or rural area? effects of the topographic masses are no longer negligible for geodetic investigations. Then we need accurate maps to navigate, but also to indicate geometric relations Quite simply: Geodesy is the science between points or landmarks depicted on the concerned with the study of the shape, size , to display information on areal extent of and gravity field of the Earth. different vegetation landuse, to design large infrastructure and transportation problems, and so on. The Earth seems to be round, is it not? In order to create accurate maps we need a well-defined . A spatial In reality the Earth is not a perfect sphere. reference system defines the coordinate system Knowledge of the exact shape of the Earth and datum in which all landmarks have a provides us with accurate maps of the Earth. unique “address” or position (i.e., coordinates).

1 Photo: iStockPhoto (dra_schwartz, hidesy, WhatWhat isis Gravitation?Gravitation? Zhenikeyev) FromFrom thethe AppleApple ......

Detailed knowledge of the Gravitational Field caps (e.g., melting due to the Greenhouse of the Earth does improve our lives, and Effect) may reduce this compression, and provides us to benefit both economically and thus change the gravitational field. socially. It helps us understand climate change, sea level rise, and geological hazards These effects are only examples. However we (e.g., earthquakes, volcanoes); and it underpins can see how complicated our planet is, and can practically all satellite applications, as well as get a sense of how these components interact precise navigation systems. with one another.

Since our planet is composed of different In the previous page we defined Geodesy as materials, its gravitational field shows local the science of studying the Shape, Size and variations (called “anomalies”). Observing these Gravity Field of the Earth. But what is the Grav- anomalies can help us to explore the sub- ity Field, and why is it important? surface mass distribution of our planet. In this way, we may look into the interior of the Earth. Gravity in a nutshell

What affects the gravitational field? Gravitation is a force that pulls or attracts all bodies in the universe that have a mass The gravitational field is affected by many towards each other. remain in their factors, including: orbits around the Sun due to this force. The gravitational force depends on the amount of „ mass density variatons inside the Earth; mass of the bodies. In Geodesy we usually distinguish “gravity” as gravitation plus cen- „ the - the level of oceans changes trifugal acceleration due to Earth's due to temperature, currents, etc. because traditionally we can measure gravity, Changes in the level of oceans also change not gravitation, at points on the rotating Earth. the gravitational field.

„ the Sun, Moon and other planets - the Newton's apple gravitational effects of the Sun, Moon and the planets vary according to their posi- Sir Isaac Newton postulated that the Earth's tion relative to the Earth. gravitation causes such things as the fabled apple to fall, yet it is the same force that keeps „ ice sheets - they compress the Earth's planets in their orbits. For example, he figured beneath them. Changes in the ice out that the Moon would travel in a straight line without the attraction from the Earth pulling it into a curved orbit.

2 ...... ToTo thethe SatellitesSatellites

Why do we need to study the gravita- world, these observations are highly confiden- tional field? tial because gravity measurements lead exploration geophysicists to oil fields and Gravitation affects almost everything in our mineral deposits, and assist military planners lives. From precise clocks to hydroelectric to guide missiles to their intended targets. dams, from the in the oceans to blood circulation. Satellite missions such as CHAMP (CHAllenging Minisatellite Payload), GRACE We study the Earth's gravitational field to (Gravity Recovery And Climate Experiment) and learn more about our planet. This knowledge GOCE (Gravity Field and Steady-state Ocean can lead us to new ways of doing things with Circulation Explorer) help us to study the global greater awareness towards of our gravitational field of the Earth. These Low-Earth Orbiters (LEOs) provide geodesists with a environment for future generations. global, homogeneous coverage of gravitational How can the satellites help? measurements. The effect of the Sumatra earthquake on If we want to study the gravitational field glo- gravity recovered from GRACE observations bally, terrestrial gravity data have severe limi- (NASA/JPL). tations, mostly because they do not cover the whole globe with a homogeneous set of mea- surements. Moreover, in some places in the

GRACE satellites observing the gravity field of the Earth

3 (Image courtesy of NASA/JPL) GeodesyGeodesy ofof TodayToday When checking the meaning of the term (illustrated in the figure by the measure- Geodesy in the major encyclopedias, we find ment of “lunar ”). it is usually described as the science concerned 4) Geodesy provides the link to (in- with the Shape, Size, and Gravity Field of the dicated by the measurement of so-called Earth. Webster’s dictionary even defines it as “lunar distances”, allowing the reconstruc- a branch of applied mathematics! tion of Universal (UT) in connection Geodesy today is much more than that. It is with astronomical almanacs). a geoscience that treats the Earth as a complex dynamic system, a body consisting of many The Space Age, and the development of space layers, surrounded by atmosphere and oceans. geodetic observation techniques associated Geodesy is required to model the system’s with it, revolutionized our understanding of behaviour in space and time so as to provide Geodesy: and distance difference mea- the basic framework needed across a wide surements complemented and, to a certain range of Earth sciences. For example, it does extent, replaced the measurement of angles, not make sense to speak of global sea level making possible the establishment of truly glo- rise without referring to the cm-accurate (time- bal reference systems (geometric and gravita- variable) terrestrial reference system, or the tional). The growth of have precise global gravity field determined from yielded positioning at the millimetre-level rou- satellite tracking, or the sea surface tine, enabling the detection of crustal move- maps established by a long ment and strain with unprecedented accuracy sequence of satellite missions. and high time resolution. Geodesy continues to provide, with state- The title page of Peter Apian’s work of-the-art measurement tools, the scientific Introductio Geographica, published in 1533, basis of Navigation, e.g., by the exploitation of proves, on the other hand, that Geodesy is a the existing and planned Global Navigation rather old science (the term Geodesy may not Satellite Systems (GNSS), such as GPS, yet have existed at that time). GLONASS, and GALILEO, and the link to fun- The illustration at the top of the page indicates damental Astronomy via the global terrestrial that: reference system, by monitoring the rotational motion of our planet, by space geodetic tech- 1) State-of-the-art measurements and their niques, and by establishing the celestial refer- correct mathematical treatment were, and ence system and UT (reflecting Earth rotation). are, of central importance. Modern Geodesy is experiencing spectacu- 2) The same measurement techniques are lar growth and each year new frontiers of Earth used for the most demanding as well as science knowledge are being explored, such as “everyday” purposes. temporal variations of positions and gravity 3) Geodetic techniques provide the basis for (land deformations, post-glacial rebound, sea applications of crucial importance and rele- level rise, etc.). It is a fundamental science, vance to mankind, such as Precise Posi- which is vital for both everyday mapping and tioning (from the global scale down to the navigation purposes, and for the scientific un- maintenance of cadastres) and Navigation derstanding of our living planet.

4 Photo: iStockPhoto (AB DESIGN)

WhyWhy isis GeodesyGeodesy FundamentalFundamental toto Society?Society?

Traditionally, Geodesy has been viewed as accuracy and better access to geodetically a service science, providing an important utility determined positions. On local to regional to other geosciences, and supporting many scales, applications such as land , applications. In the past, the main ”customers” deformation monitoring of infrasructure, of Geodesy came from the surveying and prevention and mitigation of the impacts of mapping profession, while today Geodesy environmental hazards, and numerous tech- serves all Earth sciences, including the geophysical, oceanographic, atmospheric, hydrological and communities.

Geodesy is crucial Traditionally Geodesy not only for Earth served the society by observation and providing reference science, but today frames ... it is also indis- pensable for the maintenance of many activities in a modern society. Traditionally, Geodesy has served society by providing reference frames for a wide range of practical applications, such as from regional to global navigation on land, sea and in the air, and from construction of infrastructure to the determination of reliable boundaries of real estate properties. Reference frames were, however, national or regional in scope, and they were suited for the determination of coordinates relative to a network of ground reference points. Thus, determination of precise point coordinates required simultaneous measurements at several points. Today, GNSS provides access to precise point coordinates in a global reference frame anytime and anywhere on the Earth’s surface with centimetre-level accuracy. tower (“ground reference This technological development has stimulated point”) in the Struve Chain, a member of UNESCO’s World Heritage List new applications demanding even greater

5 nical applications require more or less instan- increasing spatial and temporal resolution, taneous access to geodetic positions in a increasing accuracy, and with decreasing reliable reference frame with centimetre-level latency. accuracy or better. Already today, the economic benefit of the geodetic reference frame is The societal impacts of Space Geodesy are enormous. The availability of a global geodetic fundamental. The technological development reference frame, such as the International facilitated through the new space geodetic Terrestrial Reference Frame (ITRF), and the techniques for navigation and positioning tools to determine precise point coordinates poses new and difficult challenges, and anytime and anywhere on the Earth has a increases the requirements for accessibility, profound effect on almost all sections of accuracy and long-term stability. The new society. geodetic technologies are leading to fundamental changes not only in all areas of A deeper understanding navigation and transport, but also for of the Earth system is not Earth obser- applications in process control (e.g., farming, possible without sufficient vations are construction, mining, resource management), observations of a large set vital for the construction and monitoring of infrastructure of parameters characte- society in the (e.g., off-shore platforms, reservoirs, dams, ristic of various Earth area of disas- bridges, and other large engineering struc- system processes. Earth ter preven- tures), surveying and mapping, and Earth observations are not only tion, climate observation. Geodetic techniques are crucial necessary for a scientific change, etc. in the assessment of geohazards and anthro- understanding of the Earth, pogenic hazards, and they will play a pivotal but they are also fundamental for most societal role in early warning systems of such hazards benefit areas, ranging from disaster prevention and helping to mitigate resultant disasters. and mitigation, the provision of resources such Geodesy therefore contributes to increased as energy, water and food, achieving an security, a better use of resources, and in understanding of climate change, the general progress towards sustainable protection of the , the environment, development. and human health, and to the building and management of a prosperous global society.

Geodesy is fundamental in meeting these global challenges because it provides the foundation in which all Earth observation systems are ultimately built. But Modern Geodesy does more: with its „three pillars” of geokinematics, Earth’s gravity field, and Earth rotation, it also provides comprehensive observations of changes in the Earth’s shape, gravity field and rotation. These fundamental geodetic quantities are intimately related to mass transport in the fluid envelope of the solid Earth and its interior, as well as the dynamics of the Earth System.

Geodesy is currently in transition due to the fact that the advent of space geodetic techniques and the rapid improvement of communication technologies have funda- mentally changed, perhaps revolutionized, Geodesy and its methods. While previously point coordinates were defined with respect to local or regional reference frames, with space geodetic techniques positions can now be expressed with respect to a global reference frame with unprecedented accuracy. Based on these techniques, changes in Earth’s shape, rotation and gravity field are provided with The (a member of the World Heritage List) was established between 1816 and 1855 to determine the size and the shape of the Earth.

6 Photo: iStockPhoto (dra_schwartz, hidesy, Zhenikeyev)

TheThe AssociationAssociation

The International Association of Geodesy „ stimulating technological development, (IAG) is the scientific organization responsible and for the field of Geodesy. The origin of the IAG „ providing a consistent representation of goes back to 1862, the year, in which the the figure, rotation and gravity field of the “Mitteleuropäische Gradmessung”, pre- Earth and planets, and their temporal decessor of the IAG was established. It variations. promotes scientific cooperation and geodetic research on a global scale, and contributes to it through its various research bodies. It is an IAG objectives active member of the International Union of Geodesy and Geophysics (IUGG), which itself „ To foster geodetic research and develop- is a member of the International Council for ment, Science (ICSU). „ to support and maintain geodetic refer- ence systems, The scientific work of the Association is „ to provide observational and processed performed within a component structure data, standards, methodologies and mod- consisting of: els, „ to stimulate development of space tech- „ Commissions niques to increase the resolution of geo- „ Inter-commission Committees detic data, „ Services „ to initiate, coordinate and promote inter- „ The Global Geodetic Observing System national cooperations, and (GGOS) „ to promote the development of geodetic ac- „ The Communication and Outreach tivities across the globe, especially in de- Branch (COB), and veloping countries. „ IAG Projects IAG meetings IAG mission The IAG holds its own General Assembly The Mission of the Association is the ad- every four years in conjunction with the vancement of Geodesy, an that General Assembly of the IUGG, at the same includes the study of the planets and their sat- time and in the same country. In addition, the ellites. Association organizes Scientific Assemblies, independently from the IUGG, generally in the The IAG implements its mission by: mid-term between the General Assemblies.

„ advancing geodetic theory through re- Other meetings that the IAG sponsors or search and teaching, supports include numerous international symposia and workshops covering broad fields „ collecting, analysing and modelling obser- of Geodesy and closely associated sciences and vational data, engineering.

7 The Very Large Array radiotelescope (Image courtesy of NRAO/AUI and Laure Wilson Neish)

CommissionCommission 11 -- ReferenceReference FramesFrames IAG Commission 1 deals with geodetic caused by the motion of the tectonic plates, reference frames. These reference frames are hence the velocities of the tectonic plates can the basis for three-dimensional, time- also be estimated by monitoring these ground dependent positioning in global, regional and reference stations. national geodetic networks, for spatial Earth Orientation Parameters: reference applications such as the cadastre, engineering frames are also vital for the determination of construction, precise navigation, geo- parameters such as the direction of the Earth’s information acquisition, , sea level rotation axis, and the Earth’s rotational velocity and other geoscientific studies. and its variation. The geodetic reference frames are necessary Geocentre Motion: a reference frame clearly to consistently reference or tag parameters needs an origin. This is typically taken to be using geodetic observations, e.g., station at the centre of mass of the Earth, however coordinates, crustal motion, Earth orientation the location of this origin relative to the solid information, and so on. Ground observations Earth is not constant. Satellite techniques of GPS and other satellites, or radiotelescope provide the tool to monitor the motion of the observations of distant quasars, enable us to geocentre. define not only the reference frame, but also Commission 1 is focused on the scientific to derive other parameters such as: research associated with the definition and realization of global and regional reference Crustal motion: for example, by estimating frames, as well as the development of analysis the coordinates of continuously operating GPS and processing methods for relevant geodetic reference stations, their long-term changes in observations. coordinates can be derived. These are typically

8 Commission 2 - Gravity Field GOCE Satellite (Image courtesy of ESA) Knowledge of the Earth’s gravity field, as well variations and how they change in time is also as its temporal variation, is of prime impor- extremely important in regions of active vol- tance for Geodesy, Navigation, Geophysics, canoes where subsurface mass changes is one Geodynamics, and related disciplines. We have of the warning signals for an imminent erup- noted in the definition of Geodesy that the grav- tion. ity field is affected by many terrestrial as well as extra-terrestrial phenomena. The observa- Which way does water flow? tion of the gravity field, and the analysis and modelling of these observations, can help us This trivial question is perhaps the most find answers to important questions such as: fundamental in Geodesy because it relates to the definition of regional and national What causes the temporal variations in the grav- systems. Much effort has been expended in ity signals? the past to determine a level surface that can serve as an accessible reference for . Temporal variations in the gravity field are This reference is called the “”. Heights due to tidal forces from our Moon, Sun, and help to define the direction of water flow, and nearby planets. They are also caused by are useful to hydrological engineers and seasonal changes such as those associated oceanographers (who wish to map the oceans with hydrological systems, by changes in the currents). Gravity is inexorably intertwined Earth’s rotation, by mass redistribution in the with these concepts and provides the necessary interior of the Earth and tectonical movements, foundation for many of the related science by melting of the ice caps, etc. One can see activities already mentioned. that many of the Earth’s environments (ocean, crust, hydrosphere, polar ice caps, atmos- The Gravity Field Commission fosters and en- phere) can be investigated by studying the courages research in the areas of gravity field. „ and gravity networks, „ spatial and temporal gravity field and geoid How do the density variations of subsurface modeling, masses express themselves? „ dedicated satellite gravity mapping mis- The answer to this question is particularly sions, and important for geophysical exploration of „ regional geoid determination. natural resources, such as oil, gas, minerals, etc. However, gravity maps also help to delin- The Commission interfaces with other eate and understand active crustal re- commissions of the IAG and the Inter- gions, contour the “topography” of the ocean Commission Committee on Theory (ICCT), bottom, and help to monitor ocean currents. which plays an extremely vital role in advancing the methods of analysis and In each case, the spatial variations of gra- modelling, particularly as new types of vity are a direct consequence of subsurface instruments are developed, making possible mass variations. Understanding these new ways of observing the Earth’s gravity field.

9 The Kvarken Archipelago - a member of UNSECO’s World Heritage List (Image courtesy of the Finnish Environment Institute - FEI)

CommissionCommission 33 -- EarthEarth RotationRotation andand GeodynamicsGeodynamics The Earth is a ‘living’ planet that is con- The variations of the Earth’s gravity field and tinuously changing on its surface, as well as the deformation of the Earth’s body induced within its interior. Geodynamics is the study by the tidal forces, i.e., the forces acting on of the deformation of the Earth’s crust, which the Earth due to differential gravitation of the is mainly (but not exlusively) caused by the Sun, Moon and the planets, are called “Earth motion and collision of tectonic plates. A better Tides”. The investigation of Earth Tides is also knowledge of the movements of tectonic plates an important topic of Commission 3. It also may help us to understand the evolution of studies - among others - post-glacial rebound earthquakes and other tectonic phenomena. at all spatial scales, and also the elastic defor- mation taking place in the near-field of exist- On the other hand, the movements of the ing ice sheets and glaciers. tectonic plates are driven by material flows within the Earth’s interior. In addition, mass Commission 3 works to develop cooperation transports in the atmosphere-hydrosphere- and collaboration in computation, in theory solid Earth-core system, or the “global and in observation of Earth rotation and geophysical fluids” as they are often referred geodynamics. to, will cause observable geodynamic effects (Image courtesy of FEI) on a broad time scale. Although relatively small, these geodynamic effects have been measured by space geodetic techniques with increasing accuracy, opening up important new avenues of research that will lead to a better understanding of global mass transport processes and the Earth’s dynamic responses.

Geodynamics in the broader and most traditional sense addresses the forces that act on the Earth, whether they derive from outside or inside of our planet, and the way in which the Earth moves and deforms in response to these forces. This includes the entire range of phenomena associated with Earth rotation and Earth orientation, such as , length of (LOD) variation, and nuta- tion, the observation and understanding of which are critical to the transformation The Kvarken Archipelago between terrestrial and celestial reference in western Finland is an outstanding example of post-glacial uplift. frames. About 20000 years ago, during the last Ice Age, the centre of the continental glacier was located in this area. The ice mass pressed the earth's crust almost a kilometer downwards. As the glacier got Since the Earth is not a solid object, it thinner, the surface of the earth started to rise back. The ground is still rising, about 8 mm a year in the Kvarken area, thus new land is changes its shape if the gravity field changes. emerging from the water. 10 (Image courtesy of Charles K. Toth, OSU)

CommissionCommission 44 -- PositioningPositioning andand ApplicationsApplications

Commission 4 focuses on the Recent advances in tomographic modelling and determination of positions using various the availability of spaceborne GPS observations instruments, such as inertial navigation has also made possible 3-D profiling of electron systems (INS), Global Navigation Satellite density and atmospheric refractivity. With Systems (GNSS), InSAR (Interferometric plans for a significant increase in the number Synthetic Aperture Radar), and other of GNSS satellites in the next decade, it is clear technologies, for a wide range of that GNSS atmospheric sounding will become applications. a valuable atmospheric tool.

Commission 4 carries out research and Commission 4 also promotes research into other activities that address the broader the development of a number of geodetic tools areas of multi-sensor system theory and that have practical applications to engineering applications, with a special emphasis on and mapping. Hence there are many joint integrated guidan-ce, navigation, conferences with sister organizations such as positioning and orientation of airborne and the FIG (Inter- land-based platforms. Such systems can national Federation be used for direct georeferencing and of Surveyors) and digital imaging and scanner systems, ISPRS (International monitoring of the deformation of Society of Photo- engineering structures, navigation of grammetry and Re- people and cars, robotics, and so on. mote Sensing). GNSS, such as GPS, GLONASS, and the planned GALILEO and COMPASS systems, There are net- can also be used to monitor changes in works of permanent the atmosphere. Due to the fact that the GPS stations estab- GNSS signals travel through the lished locally, regio- atmosphere, they can be used to derive nally and globally to some important parameters such as: perform not only geodetic research, „ the total electron content of the iono- but also to support sphere, and surveying, engi- „ the precipitable water vapour in the neering, precise na- troposphere. vigation, and data acquisition for Geo- Thus GNSS systems are also used to spatial Information (Image courtesy of M. Bevis) enhance the near real-time water vapour Systems (GISs). estimation, which is useful for weather Permanent GPS Station in southern forecasting. Greenland, part of the GNET project

11 IAGIAG ICCICC onon IAGIAG Photo: iStockPhoto (Georgo, catherine_jones) TheoryTheory (ICCT)(ICCT) PublicationsPublications

The InterCommission Committee on Theory The IAG Publications include: (ICCT) was established to interact actively and „ the Journal of Geodesy; directly with other IAG entities. Recognizing „ the Geodesist’s Handbook; that geodetic observing systems have advanced „ the IAG Newsletter; to such an extent that geodetic measurements „ the “Travaux de l’Association (i) are now of unprecedented accuracy and Internationale de Géodésie”; quality, can readily cover a region of any scale „ the IAG Special Publications; and up to tens of thousands of kilometres, yield „ the IAG Symposia series. non-conventional data types, and can be The Journal of Geodesy is an international provided continuously; and (ii) consequently, journal concerned with the study of scientific demand advanced mathematical modelling in problems of Geodesy and related order to obtain the maximum benefit of such interdisciplinary sciences. Peer-reviewed technological advance, the ICCT papers are published on theoretical or modelling studies, and on results of „ strongly encourages frontier experiments and interpretations. mathematical and physical research, directly motivated by geodetic need/practice, as a Every four years after a General Assembly, contribution to science/engineering in general the IAG publishes The Geodesist’s Handbook. and the foundations of Geodesy in particular; This Handbook provides information on the As- „ provides the channel of communication sociation, including the reports of the Presi- amongst the different IAG entities of dent and Secretary General, the resolutions, commissions/services/projects on the ground and the Association structure. of theory and methodology, and directly cooperates with and supports these entities The IAG Newsletter is published monthly in the topic-oriented work; electronically. A reduced version is also published in the Journal of Geodesy regularly. „ helps the IAG in articulating The original Newsletters are available at the mathematical and physical challenges of IAG website: http://www.iag-aig.org. Geodesy as a subject of science and in attracting young talents to Geodesy. The ICCT After each General and Scientific Assembly, strives to attract and serve as home to math- a collection of the reports by the Association ematically motivated/oriented geodesists and components is published in the “Travaux de to applied mathematicians; and l’Association Internationale de Géodésie” „ encourages closer research ties with and electronically. Printed copies are available on gets directly involved in relevant areas of the request. Earth sciences, bearing in mind that Geodesy has been always playing an important role in Proceedings of IAG symposia are typically understanding the physics of the Earth. published in the IAG Symposia Series.

12 Photo: iStockPhoto (hidesy), NRAO/AUI and Laure Wilson IAGIAG ServicesServices Neish The IAG is the home of a number of scientific services whose goals are to provide the user IBS (IAG Bibliographic Service) community with various geodetic products URL:http://www.bkg.bund.de and/or information and to foster international The service maintains a literature database for cooperation. geodesy, photogrammetry and (GEOPHOKA), which is housed at the federal agency BKG (Bundesamt für Kartografie und BGI (Bureau Gravimetrique Interna- Geodäsie), in Germany. tional) URL: http://bgi.cnes.fr ICET (International Centre for Earth The main task of the BGI is to collect, on a Tides) worldwide basis, all existing gravity measurements and pertinent information URL: http://www.astro.oma.be/ICET about the gravity field of the Earth, to compile The ICET collects all available measure- them and store them in a computerized ments on Earth Tides. It evaluates these data database, and to redistribute them on request in order to reduce the very large amount of to scientific users. measurements to a limited number of param- eters which contain all required geophysical information, and compares the data from dif- BIPM (Bureau International de Poids ferent instruments and different stations dis- et Measures) -Section Time, Fre- tributed all over the world. quency and Gravimetry URL: http://www.bipm.org/en/scientific/tfg/ ICGEM (International Center for Glo- The Bureau International des Poids et bal Gravity Field Models) Mesures (BIPM) is responsible for the maintenance of the International Atomic Time URL: http://icgem.gfz-potsdam.de/ICGEM (TAI) scale and of the Coordinated Universal The ICGEM collects all existing gravity field Time (UTC) scale. The BIPM ensures that TAI models and provides on-line interfaces to and UTC are available in the standards download and visualize these models, and to laboratories around the world, and is calculate functionals (e.g., geoid heights or responsible for the worldwide coordination of gravity anomalies) from these models on user- time comparisons. defined geographic grids.

IAS (International Altimetry Service) IDEMS (International Digital Eleva- URL:http://ias.dgfi.badw.de tion Model Service) URL: http://www.cse.dmu.ac.uk/EAPRS/iag The IAS ·provides a point of contact for general information on satellite altimetry and The IDEMS collects and validates digital rep- its applications; promotes satellite altimetry as resentations of the global topography (Digital a core element of Global Earth Observing Sys- Models-DEMs). The centre of IDEMS tems; and helps users to compile and analyse places a particular emphasis on water repre- data. sentation in DEMs.

13 IDS (International DORIS Service) IGS (International GNSS Service) URL: http://ids.cls.fr URL: http://igscb.jpl.nasa.gov The primary objective of the IDS is to oper- The Global (GPS) is an ate a service to provide Doppler Orbitography extremely versatile technology that enables and Radiopositioning Integrated by Satellite precise ground and space-based positioning, (DORIS) data and data products, useful to a timing and navigation anywhere in the world. wide range of scientific and practical applica- The use of GPS and GNSS, particularly for tions. Earth sciences applications, stems largely from activities of the International GNSS Ser- vice (IGS). More than 200 organizations in 80 IERS (International Earth Rotation countries contribute daily to the IGS, which is and Reference Systems Service) dependent upon a cooperative global tracking URL: http://www.iers.org network of over 350 GPS stations. The primary objectives of the IERS are to IGS provides various important data and serve the astronomical, geodetic and products to the users. geophysical communities by providing the following: a) The International Celestial Reference System (ICRS) and its realization, the ILRS (International Laser Ranging International Celestial Reference Frame (ICRF); Service) URL: http://ilrs.gsfc.nasa.gov b) The International Terrestrial Reference System (ITRS) and its realization, the The ILRS collects, merges, analyzes and International Terrestrial Reference Frame distributes (SLR) and (ITRF); c) Earth orientation parameters required Lunar Laser Ranging (LLR) observation data to study Earth orientation variations and to sets of sufficient accuracy to satisfy a wide range of applications. The basic observable is transform between the ICRF and the ITRF; d) the precise time-of-flight of a laser pulse to Geophysical data to interpret time/space and from retroreflectors on a satellite (in the variations in the ICRF, ITRF or Earth case of SLR), and on the Moon (in the case of orientation parameters, and model such LLR). variations; e) Standards, constants and models, and encouraging international adherence to its conventions. IVS (International VLBI Service for Geodesy and Astrometry) URL: http://ivscc.gsfc.nasa.gov IGeS (International Geoid Service) URL: http://www.iges.polimi.it The IVS coordinates Very Long Baseline The main tasks of the IGeS are to collect (VLBI) observing programs, sets software and data referring to the geoid, vali- performance standards for VLBI stations, date them and disseminate them upon request develops conventions for VLBI data formats among the scientific community. IGeS is also and data products, issues recommendations organizing regularly the “International School for VLBI data analysis software, sets standards on the Determination and Use of the Geoid”. for VLBI analysis documentation, and institutes appropriate VLBI product delivery methods to ensure suitable product quality IGFS (International Gravity Field Ser- and timeliness. vice) URL: http://www.igfs.net IGFS is a unified service which is responsible PSMSL (Permanent Service for Mean for gravity data collection, validation, archiving Sea Level) and dissemination, as well as software URL: http://www.pol.ac.uk/psmsl collection, evaluation, dissemination for the The PSMSL is responsible for the collection, purpose of determining, with various degrees publication, analysis and interpretation of sea of accuracy and resolution, the Earth’s surface level data from the global network of and gravity potential, or any of its functionals. gauges. These data are used for a wide range The temporal variations of the gravity field are of scientific uses, including the long-term sea also studied. It comprises BGI, ICET, ICGEM, level change assessments of the IDEMS, IGeS and IAS. Intergovernmental Panel on Climate Change (IPCC). The PSMSL also manages the delayed- mode activity of the Global Sea Level Observing System (GLOSS).

14 The Global Geodetic Photo: GGOS Observing System (GGOS)

The Global Geodetic Ob- GGOS contributes to the Global Earth serving System (GGOS) Observing System of Systems (GEOSS) not only was established by the with the accurate reference frame required for IAG in July 2003 as a many components of GEOSS but also with project. In April 2004 the observations related to the global hydrological IAG, represented by cycle, the dynamics of the atmosphere and the GGOS, became a partici- oceans, and geohazards. GGOS acts as the pating organization of interface between the geodetic services the Group on Earth Ob- andexternal users such as GEOSS, IGOS-P, servations (GEO), in May 2006 GGOS was ac- and United Nations authorities. A major goal cepted as a member of the Integrated Global is to ensure the interoperability of the IAG Observation Strategy Partnership (IGOS-P) and services and GEOSS. in July 2007 at the IUGG General Assembly GGOS became an official component of the IAG, i.e., the Global Geodetic Observing Sys- tem of the IAG.

GGOS provides observations of the three fundamental geodetic observables and their variations, that is, the Earth’s shape, the Earth’s gravity field, and the Earth’s rotational motion.

GGOS integrates different geodetic techniques, different models and different approaches in order to ensure a long-term, precise monitoring of the geodetic observables in agreement with the Integrated Global Observing Strategy (IGOS). GGOS provides the observational basis to maintain a stable, accurate and global reference frame, and in this function is crucial for all Earth observation

and many practical applications. (Image courtesy of NERC,UK)

The Herstmonceaux Satellite Laser Ran- ging Telescope in operation

15 GGOS is built on the IAG Services (IGS, IVS, consisting mainly of high quality services, ILRS, IDS, IERS, IGFS, etc.) and the products standards and references, theoretical and they derive on an operational basis for Earth observation innovations. monitoring making use of a large variety of space- and ground -based geodetic techniques, GGOS and its related research and Services’ such as Very Long Baseline Interferometry porducts will address the relevant science (VLBI), Satellite and Lunar Laser Ranging (SLR/ issues related to geodesy and geodynamics in LLR), Global Navigation Satellite Systems the 21st century, but also issues relevant to (GNSS), Doppler Orbitography and society (global risk management, geo-hazards, Radiopositioning Integrated by Satellite natural resources, climate change, severe (DORIS), altimetry, InSAR (Interferometric storm forecasting, sea-level estimations and Synthetic Aperture Radar) and gravity satellite ocean forecasting, space weather, and others). missions (CHAMP, GRACE, GOCE), gravimetry, It is an ambitious program of a dimension that etc. goes beyond IAG, requring a strong cooperation within the geodetic, geodynamic and geophysical communities, and externally, to All of these observation techniques are considered integral parts of GGOS, allowing the related endeavours and communities. monitoring of the Earth’s shape and deformation (including water surface), the Earth’s orientation and rotation and the Earth’s gravity field and its temporal variations with an unprecedented accuracy. The observed quantities give direct evidence of many global processes that have a crucial impact on human society such as earthquakes, volcanism, floods, sea level change, climate change, water redistribution, mass balance of the polar ice sheets, post-glacial rebound, etc.

Mission

The mission of GGOS is to promote the application of geodetic Earth observation methods to the solution of Earth science problems. GGOS accomplishes its mission: a) by defining the geodetic infrastructure that is needed to meet scientific and societal requirements; b) by advocating for the establishment and maintenance of this geodetic infrastructure; c) by coordinating interaction between the IAG Services, Commissions or other geodetic entities; d) by improving accessibility to geodetic observations and products; and e) by educating the scientific community about the benefits of geodetic research and the public about the role that Observing the Earth with various geodetic methods Geodesy plays in society. (Very Long Baseline Interferometry, GPS, DORIS, Low Earth Orbiters - LEO, Altimetry, SLR, LLR) GGOS provides the basis on which future advances in geosciences can be built. By considering the Earth system as a whole (including the geosphere, hydrosphere, For more information, please visit the GGOS cryosphere, atmosphere and biosphere), website: monitoring Earth system components and tehir interactions by geodetic techniques and studying them from the geodetic point of view, http://www.ggos.org the geodetic community provides the global geosciences community with a powerful tool

16 LinksLinks Photo: iStockPhoto (sweetym) International Union of Geodesy International Union of Geological and Geophysics (IUGG) Sciences (IUGS) (www.iugg.org) (www.iugs.org) The IUGG comprises of the following seven International Federation of Survey- semi-autonomous Associations beside IAG: ors (FIG) (www.fig.net) International Association of Cryospheric Sciences (IACS) International Society for Photogram- (www.cryosphericsciences.org) metry and Remote Sensing (ISPRS) International Association of Geo- (www.isprs.org) magnetism and Aeronomy (IAGA) International Cartographic Associa- (www.iugg.org/IAGA) tion (ICA) International Association of Hydro- (cartography.tuwien.ac.at/ica) logical Sciences (IAHS) (http://iahs.info) International Society of Mine Survey- ing (ISM) International Association of Meteo- (www.ism.bw-art.de) rology and Atmospheric Sciences (IAMAS) International Hydrographic Organi- (www.iamas.org) zation (IHO) (www.iho.shom.fr) International Association for the Physical Sciences of the Oceans American Geophysical Union (AGU) (IAPSO) (www.agu.org) (iapso.iugg.org) European Geosciences Union International Association of Seis- (EGU) mology and Physics of the Earth’s (www.copernicus.org/EGU/EGU.html) Interior (IASPEI) (www.iaspei.org) Global Spatial Data Infrastructure Association (GSDI) International Association of Volca- (www.gsdi.org) nology and Chemistry of the Earth’s Interior (IAVCEI) Federation of Astronomical and (www.iavcei.org) Geophysical Data Analysis Services (FAGS) Links to other organizations: (www.icsu-fags.org)

International Astronomical Union The Institute of Navigation (IAU) (www.ion.org) (www.iau.org)

17 Photo: iStockPhoto (Andrew MembershipMembership IAGIAG COBCOB Johnson, andipantz) The membership of the IAG comprises The Communication and Outreach Branch countries and individuals. Any member (COB) provides the IAG with communication, country of the IUGG is regarded as a National educational/public information and outreach Member of the IAG and may, through its links to the membership, to other scientific adhering body, appoint a National Delegate to associations and to the world as a whole. the Association. National Delegates represent their countries in IAG Council meetings and The responsibilities of the COB include act as correspondents for their countries promotion of the IAG (at meetings and between General Assemblies. Individual conferences), membership development, scientists may become Members and Fellows maintenance of the IAG website, publications of the IAG. The IAG Executive Committee, upon (newsletters), and creation of a resource base the recommendation of the Secretary General, for educators, developing countries and our accepts individuals as Members. Applications global community. for individual membership are made to the Bureau. The COB maintains the official IAG website, where one can find all the latest news about Benefits of individual membership include IAG and Geodesy in general. substantial reduction on the individual subscription rate to the Journal of Geodesy, the right to participate in the IAG election For further information please browse the process both as a nominator and a nominee, IAG website, or contact us on the following e- and a reduction of the registration fee for many mail address: IAG meetings. The individual members also receive the monthly IAG Newsletter. URL: http://www.iag-aig.org E-mail: [email protected] IAG Members have access to the Members’ Area of the IAG website, where they can browse Acknowledgements: This brochure has been prepared, among the contact data of other international under the supervision of the IAG Executive Committee, in scientists. The Members’ Area contains arrangement of the IAG Communication and Outreach electronic materials related to the latest Branch (COB). Contributions to this brochure came from many sources, especially the IAG entities (Commissions, achievements of Geodesy. GGOS, Services) Chairs and the new IAG Statutes and By- laws, supplemented by valuable suggestions from the IAG Central Bureau, the COB Steering Committee (SC) serv- IAG Members are entitled to use the private ing in 2003-2007 and a number of individual scientists. A billboard service of the IAG website to exchange first draft text, synthesizing the original input material was their views about issues related to Geodesy. prepared by József Ádám (COB President), Szabolcs Rózsa (COB Secretary) and Markku Poutanen (COB SC Mem- Past Officers of the Association are eligible ber). Revisions and additional material were provided by to become Fellows and are invited to become Riccardo Barzaghi, Gerhard Beutler, René Forsberg, Chris Jekeli, Ron Noomen, Chris Rizos, Fernando Sansó, Michael such. The IAG Executive Committee makes G. Sideris and C. Christian Tscherning. The contribution these appointments. of Szabolcs Rózsa to its design and for the editing is par- ticularly acknowledged.

18 Official IAG Website: http://www.iag-aig.org Website of the IAG Office: http://iag.dgfi.badw.de

Commissions:

Commission 1 - Reference Frames Commission 2 - Gravity Field Commission 3 - Earth Rotatation and Geodynamics Commission 4 - Positioning and Applications

ICCT (InterCommission Committee on Theory)

Services: BGI - International Gravitmetric Bureau http://bgi.cnes.fr BIPM - Bureaus International de Poids at Measures - http://www.bipm.org/en/ Section Time, Frequency and Gravimetry scientific/tfg IAS - International Altimertry Service http://ias.dgfi.badw.de IBS - IAG Bibliographic Service http://www.bkg.bund.de ICET - International Centre for Earth Tides http://www.astro.oma.be/ICET

ICGEM - Int.Center for Global Earth Models http://icgem.gfz/potsdam.de/ ICGEM IDEMS - International DEM Service http://www.cse.dmu.acu.uk/ EAPRS/iag/ IDS - International DORIS Service http://ids.cls.fr IERS - Int. Earth Rotation and Ref. Frames Service http://www.iers.org IGeS - International Geoid Service http://www.iges.polimi.it IGFS - International Gravity Field Service http://www.igfs.net IGS - International GNSS Service http://igscb.jpl.nasa.gov ILRS - International Laser Ranging Service http://ilrs.gsfc.nasa.gov IVS - International VLBI Service http://ivscc.gsfc.nasa.gov PSMSL - Permanent Service for Mean Sea Level http://www.pol.ac.uk/psmsl

GGOS (Global Geodetic Observing System) http://www.ggos.org

IAG Office IAG Communication and Outreach Branch Deutsches Geodaetisches Department of Geodesy and Surveying Forschungsinstitut HAS-BME Res. Group for Phys. Geod. and (DGFI) Geodynamics Alfons Goppel Str. 11. Budapest University of Technology and D-80539 Economics Germany H-1521 Budapest P.O. Box. 91 E-mail: [email protected] Hungary E-mail: [email protected]