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Die moderne Satellitengeodasie liefert uns eine Fulle an Beobachtungsdaten, die uns Informationen uber eine Vielzahl an Prozessen im System Erde liefern. Teilweise tragen diese Prozesse ein erhebliches Zerstorungspotenzial in sich, und somit ist die kontinuierliche Erfassung von kleinsten Veranderungen von groser Bedeutung. Die trage Bewegung tektonischer Platten von einigen Millimetern bis Zentimetern pro Jahr kann plotzliche Erdbeben mit Deformationen von mehreren Metern auslosen. Erdbeben im Ozean konnen Tsunamis verursachen, die beim Auftreffen auf die Kuste eine mindestens so grose zerstorerische Kraft haben wie das Erdbeben selbst. Wesentlich gemachlichere, aber langfristig nicht minder bedrohliche Vorgange zeigen sich in den Weltmeeren durch Veranderungen der Meeresoberflache. Wir messen fur den Meeresspiegelanstieg einen globalen Durchschnittswert von mehr als 3 Millimetern pro Jahr, allerdings mit grosen regionalen Unterschieden. Durch unterschiedliche geodatische Messverfahren konnen wir sogar die Schuldigen dafur identifizieren. Einer der Hauptdelinquenten sind die grosen Eisschilde in Gronland und der Antarktis, die zusammen aktuell fast 500 Gigatonnen an Eismasse pro Jahr an die Ozeane verlieren. Grose Wassermassenveranderungen beobachten wir auch in den Kontinenten, beispielsweise durch grosraumige Veranderung von Grundwasserstanden. Das Verstandnis des globalen Wasserkreislaufs ist hinsichtlich der Verfugbarkeit von Trink- und Nutzwasser gesellschaftlich hochst relevant, genauso wie das Schadenspotenzial durch Fluten und Durren. Viele dieser Phanomene sind Indikatoren fur nachhaltige Veranderungen im Klimasystem unseres Planeten.

Heute sind wir mit modernen geodatischen Beobachtungsverfahren in der Lage, die geometrische Figur, das Rotationsverhalten und das Schwerefeld der Erde sowie deren zeitliche Veranderungen mit extrem hoher Genauigkeit aus dem Weltraum zu vermessen. Als Grundlage dafur benotigen wir einen globalen und langzeitstabilen Bezug: ein geodatisches Referenzsystem. Milliarden von Nutzern schatzen das Potenzial globaler Satellitennavigationssysteme (GNSS), deren Einsatzbereiche in den vergangenen Jahren geradezu explodiert sind, und die unseren Alltag tief durchdrungen haben. Neben GNSS gibt es aber noch weitere Beobachtungsverfahren, die fur die Vermessung unseres Planeten von zentraler Bedeutung sind. Dazu gehoren Laserentfernungsmessungen, mit denen Satellitenbahnen und Positionen auf der Erde hochgenau bestimmt werden konnen. Die Radioastronomie ermoglicht durch den Empfang von Radiosignalen entfernter Galaxien die prazise Bestimmung der Orientierung unseres Planeten im Weltraum. Die Satellitenaltimetrie vermisst mit einem aktiven Radarsystem die Meeresoberflache zentimetergenau und kann damit auch Veranderungen des Meeresspiegels zuverlassig bestimmen. Satellitenmissionen zur Vermessung des Erdschwerefeldes liefern wichtige Informationen, um die Massenverteilung der Erde und Massentransportprozesse wie das Abschmelzen der Eisschilde zu detektieren.

Die hochgenauen Satellitendaten liefern wertvolle Beitrage fur ein weitgefachertes Aufgabenspektrum unserer modernen Gesellschaft. Ein fundamentales geodatisches Produkt sind globale Referenzrahmen, die einen einheitlichen Bezug fur alle raumbezogenen Daten (Geoinformationen) weltweit gewahrleisten. Dies ist unabdingbar fur alle Positionierungsaufgaben, die Satellitennavigation sowie ein genaues Kataster-, Land- und Ressourcenmanagement. Die prazisen Satellitenbeobachtungen sind ebenso unverzichtbar, um die Veranderungen unseres Planeten verlasslich zu erfassen und auf diese Weise wichtige Informationen fur die Erforschung des Erdsystems zu generieren. Die geodatischen Beobachtungen liefern die Grundlage fur die Bestimmung der Auswirkungen des Klimawandels sowie fur die Entwicklung und den Betrieb von Warnsystemen zum Schutz vor Naturgefahren. Drei gesellschaftlich besonders relevante Themenbereiche werden naher beleuchtet: die Satellitennavigation, die Erdsystemforschung und der Klimawandel. Mit Interviewbeitragen der renommierten Fachexperten Gunter Hein, Harald Lesch und Stefan Rahmstorf wird die satellitenbasierte Sicht „von oben“ durch deren Einblicke „von ausen“ wesentlich erweitert.

Das Jahr 1957 markiert einen wichtigen Meilenstein in der Entwicklungsgeschichte der Geodasie: Mit dem Start des ersten kunstlichen Satelliten Sputnik 1 wird die Vermessung der Erde geradezu revolutioniert. Die Geodasie ist eine der altesten Wissenschaften der Welt. Ihre Anfange liegen bereits um etwa 8000 v.Chr., als die Menschen begannen, landwirtschaftliche Flachen zu bewirtschaften. Fruhe Hochkulturen in Agypten und Mesopotamien verfeinern ihre vermessungstechnischen Fertigkeiten, und im alten Rom waren Bauprojekte wie Brucken, Tunnel und Wasserleitungen ohne Geodasie undenkbar. Mindestens ebenso alt ist die Frage nach der Form der Erde: Scheibe, Kugel oder Ellipsoid? Auf dem Weg zur Klarung dieser Frage begegnen uns die wohl grosten Namen in der Geschichte der Naturwissenschaften: Galilei, Kepler, Newton, Gaus, Humboldt, Helmert und letztlich auch Einstein. Abenteuerliche, jahrelange Expeditionen in abgelegene Lander werden durchgefuhrt, um die Abplattung der Erde an den Polen zu bestimmen. Letztlich konnte diese aus wenigen Wochen an Sputnik-Bahndaten viel genauer ermittelt werden als es davor in jahrtausendelangen Bemuhungen gelungen ist.

The DTRF2008 is a realization of the ITRS computed by the ITRS Combination Centre at DGFI. It is based on the same input data as the ITRF2008. In order to assess the internal and external accuracy of DTRF2008 several validation procedures are applied which are based on comparisons with technique-only multi-year solutions (for assessing the internal accuracy) and comparisons with ITRF2008 and ITRF2005 (for assessing the external accuracy). The analysis is done separately for the four space-geodetic techniques GPS, VLBI, SLR and DORIS. The internal accuracy for station positions is between 0.6 and 3.3mm and the external accuracy between 7 and 10mm depending on the space technique. For the velocities the internal accuracy is between 0.25 and 1.0mm/a and the external between 0.2 and 2.0mm/a.

The International Terrestrial Reference System (ITRS) is defined by the IERS Conventions as a geocentric system with the origin in the Earth’s centre of mass. It is realized by a crust-fixed frame of reference stations (ITRF). The paper deals with alternative realizations of these specifications with the high accuracy needed in geosciences research.

Geodetic reference systems are fundamental requisites for accurate and reliable geodetic results. Unambiguous reference systems are needed to refer the geodetic observations and estimated parameters to a unique global basis. Highly accurate, consistent and reliable realizations of the terrestrial reference systems are required for measuring and mapping the Earth’s surface and its variations in time. These terrestrial reference frames are the basis for many practical applications, such as national and regional geodetic networks, engineering, precise navigation, geo-information systems, etc. as well as for scientific investigations in the Earth’s system (e.g., tectonic plate motion, sea level change, seasonal and secular loading signals, atmosphere dynamics and Earth orientation excitation).

The GGOS-D terrestrial reference frame has been computed in a common adjustment of station positions and velocities together with the Earth orientation parameters and the quasar coordinates (celestial reference frame). The data were processed as datum-free normal equations from homogeneously generated VLBI, SLR and GPS observation time series using identical standards for the modelling and parameterization. A major focus was on the analysis of the station position time series, investigations regarding seasonal variations in station motions and on the combination methodology for the terrestrial reference frame computation.

The Global Geodetic Observing System (GGOS) is the contribution of the International Association of Geodesy (IAG) to the Global Earth Observing System of Systems (GEOSS). The implementation of common standards and conventions in all components of GGOS is of crucial importance to ensure highest accuracy of geodetic and geophysical products. Consistency with relevant external standards and conventions is mandatory to achieve interoperability with GEOSS.

The GGOS-D global terrestrial reference frame has been computed from a combination of homogeneously processed VLBI, SLR and GPS observation time series. A major focus was on the analysis of station position time series, investigations regarding the handling of non-linear station motions, and the development of refined combination methods. The terrestrial reference frame (station positions and velocities) has been estimated simultaneously with the Earth orientation parameters and the celestial reference frame (quasar coordinates).

In its function as an ITRS Combination Centre DGFI has computed a solution of the International Terrestrial Reference Frame 2005 (ITRF2005). It is based on the combination of epoch normal equations (weekly or session data sets, respectively) of station positions and Earth Orientation Parameters (EOPs) from the geodetic space techniques VLBI, SLR, GPS and DORIS. The procedure includes the datum free accumulation of technique-specific normal equations, the inter-technique combination using local tie measurements at co-location sites, and the computation of the ITRF2005 solution.

ITRF2005 is the first terrestrial reference frame computed from weekly/ session-wise data sets of the geodetic space techniques GPS, VLBI, SLR and DORIS. This allows to detect time variable effects in station positions, such as discontinuities or seasonal variations. In the combination of the terrestrial reference frame these time variable effects need to be taken into account.

This paper presents the results of different methods that have been applied to investigate the strength of SLR observations to realize the scale and origin of the terrestrial reference system. In this context the effect of the network geometry and the satellite altitude has been studied by analysing the covariance matrix of the datum parameters. Furthermore, the time series of the scale and translation parameters of weekly SLR network solutions were analysed from 1993 until 2007 and the effect of range bias estimation has been investigated

In its function as an ITRS Combination Center, DGFI has developed refined methods for the terrestrial reference frame computation. The advanced approach is based on the combination of epoch normal equations (weekly/daily data sets) containing Station positions and Earth orientation parameters (EOP) obtained from different geodetic space techniques such as VLBI, SLR, GPS and DORIS. This refined approach allows to account for nonlinear effects (e.g., periodic signals and discontinuities) in Station positions and to ensure consistency between TRF and EOP. The ITRF2004 submissions were used as input for a refined realization of the terrestrial reference frame. This paper presents the combination methodology and the current Status of the ITRF2004 computations at DGFI.

The most precise space geodetic techniques for the realization of global terrestrial reference systems are VLBI, SLR and GPS. We focus on the contribution of these techniques to the determination of the vertical component. We discuss the strengths and weaknesses of each of the technique regarding the height determination as well as the effect of systematic errors. The quality of the ITRF (especially with respect to the vertical component) is assessed. Finally VLBI, SLR and GPS time series of position estimates are used to discuss the time—dependent stability of the solutions.

This paper deals with the estimation of geocenter variations on the basis of SLR data to LAGEOS 1 and 2. The paper describes the SLR data analysis with the DGFI software DOGS. We computed a combined LAGEOS 1 & 2 solution, and in addition two separate solutions using the data of both satellites independently. For the estimation of geocenter variations we applied a geometric and an analytic method. The results obtained from these different approaches were used to assess the accuracy and consistency of the geocenter determination. Finally we compared our estimates with other space geodetic and geophysically derived results. We found a good agreement for the annual amplitudes and phases, whereas the semiannual signals differ significantly.

In cooperation with various organizations in the host countries, the GFZ Potsdam established the large-scale GPS network SAGA (South American Geodynamic Activities) covering Chile and parts of Argentina. The network consists of 215 sites including two sites on the islands Robinson Crusoe and San Felix that are part of the Nazca plate.

Efforts to measure the Earth’s gravity field over the surface of the Earth or ocean have been made since several decades. Terrestrial static gravity observations are limited in coverage and homogenity due to economical and topographical reasons. Shipborne gravity measurements are restricted to a few special areas of oceans because of the expense. Both methods have logistical difficulties and efficiency problems. Satellite surveying techniques have greatly improved our knowledge of the Earth’s gravity field. However, due to the altitude of the satellites above the Earth, only data with lower resolution rate are available. A detailed study of the Earth’s gravity field provides the motivation for accomplishing airborne gravimetry techniques.

The joint effort of geo-institutions from four states of the CIS and the GeoForschungsZentrum Potsdam has resulted in the design, monumentation and observation of a 40 points GPS network in one of the most complex zone of continental collision between the Eurasian and Indian plates. The network covers the states of Usbekistan, Kirgistan and part of Kasachstan and has an extension of about 1.000 × 500 km. One point in the network (Kitab) is belonging to the global GPS fiducial station network, running permanently a ROGUE receiver. Another point (Maidanak) was tied to the nearby 3rd generation SLR station. By two joint teams the monumentation of the network was carried out in May/June 1992 following CSTG/SGMS monumentation standards. The first observation campaign was run in August 1992 by 11 joint teams equipped with TRIMBLE 4000 SST receivers, automatic meteo stations, generators, etc. Four corner points of the network were occupied permanently, the rest of the network was observed by seven moving teams in 6 sessions. First data analysis results have been obtained by processing the Trimble data from the regional network simultaneously with the global IGS core network data. Investigations of daily global dynamic solutions proof a baseline repeatability of 1.10−8.