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At the beginning of the year 2023, the DTRF2020, the ITRS 2020 realization of DGFI-TUM was completed. In this presentation, we closely look at the results of the analysis of the DTRF2020 Earth Orientation Parameter (EOP) series. First, we examine the impact of accounting for non-tidal loading on the EOP time series of each observation technique. In particular, changes in the annual and semi-annual signals of the EOP series can be expected, as both frequencies are dominant in the non-tidal loading displacements of the observing stations. We analyze the combined DTRF2020 EOP time series in terms of their temporal changes and their sensitivity to the contributing techniques, and we compare them to reference series such as IERS Bulletin A, IERS 20 C04, and SPACE 2018 (or a later version). Furthermore, we investigate the achieved consistency with the ITRF2020 and JTRF2020 in terms of the EOP, since these solutions have been computed from the same input data. A comparison with the DTRF2014 EOP reflects the consistency of successive DTRF solutions., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

The accurate knowledge of the Earth’s orientation and rotation in space is essential for a broad variety of scientific and societal applications. Among others, these include global positioning, near-Earth and deep-space navigation, the realisation of precise reference and time systems as well as studies of geodynamics and global change phenomena. In this paper, we present a refined strategy for processing and combining Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), Global Navigation Satellite Systems (GNSS), and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) observations at the normal equation level and formulate recommendations for a consistent processing of the space-geodetic input data. Based on the developed strategy, we determine final and rapid Earth rotation parameter (ERP) solutions with low latency that also serve as the basis for a subsequent prediction of ERPs involving effective angular momentum data. Realising final ERPs on an accuracy level comparable to the final ERP benchmark solutions IERS 14C04 and JPL COMB2018, our strategy allows to enhance the consistency between final, rapid and predicted ERPs in terms of RMS differences by up to 50% compared to existing solutions. The findings of the study thus support the ambitious goals of the Global Geodetic Observing System (GGOS) in providing highly accurate and consistent time series of geodetic parameters for science and applications.

Among the continuous (CONT) campaigns of very long baseline interferometry (VLBI), CONT17 is a special CONT campaign which comprises three independent networks: two legacy networks, and one VGOS network to mainly check possible biases in network geometry. In this study, we estimate all types of geodetic parameters (station and source coordinates, and Earth orientation parameters (EOP)) within the single networks and compare them to investigate potential network dependent biases. Since the separate networks are technically linked to each other by common parameters, i.e. EOP and common radio source coordinates, they can be regarded as a single network on the Earth and integrated in one common adjustment. Thus, we also estimate the station and source coordinates, and the EOP from the integrated networks and compare them with those of the single networks to check the impact on the geodetic parameters. There are both subtle and large biases (up to 7.1 mm between the legacy networks in the Ty component and 23.3 mm between the legacy and VGOS networks in the $$D_3$$ D 3 component on the surface of the Earth) between the single networks depending on parameter types. The integrated network eventually compensates those differences. Adding the VGOS network to the legacy networks does not show any significant improvement for the latter. However, the integration can provide the VGOS network with better parameter estimates which is important for the new stations.

In 2016, three new realizations of the International Terrestrial Reference System (ITRS), namely DTRF2014, ITRF2014, and JTRF2014, have been released. In this paper, we evaluate these ITRS realizations for precise orbit determination of ten high and low Earth orbiting geodetic satellites using satellite laser ranging (SLR) observations. We show the reduction of observation residuals and estimated range biases, when using these new ITRS realizations, as compared to the previous ITRS realization for SLR stations -- SLRF2008. Thus, the mean SLR root-mean-square (RMS) fits reduce (improve), on average over all satellites tested, by 3.0, 3.6, 8.1, and 7.7 % at 1993.0 - 2015.0, when using ITRF2014, DTRF2014, DTRF2014 with non-tidal loading, and JTRF2014 realizations, respectively. The improvement of the RMS fits is even larger at 2015.0 - 2017.0: 14.0 and 15.5 % using ITRF2014 and DTRF2014, respectively. For the altimetry satellite Jason-2, we found improvements in the RMS and mean of the sea surface height crossover differences with the new ITRS realizations, as compared to SLRF2008. We show that JTRF2014, after an editing done for SLR stations Conception and Zimmerwald, and DTRF2014 with non-tidal loading corrections result in the smallest RMS and absolute mean fits of SLR observations indicating the best performance among the ITRS realizations tested, while using SLRF2008 and ITRF2014 causes a 0.2-0.3 mm/y trend in the mean of SLR fits at 2001.0-2017.0.

The Celestial Reference System (CRS) is currently realized only by Very Long Baseline Interferometry (VLBI) because it is the space geodetic technique that enables observations in that frame. In contrast, the Terrestrial Reference System (TRS) is realized by means of the combination of four space geodetic techniques: Global Navigation Satellite System (GNSS), VLBI, Satellite Laser Ranging (SLR), and Doppler Orbitography and Radiopositioning Integrated by Satellite. The Earth orientation parameters (EOP) are the link between the two types of systems, CRS and TRS. The EOP series of the International Earth Rotation and Reference Systems Service were combined of specifically selected series from various analysis centers. Other EOP series were generated by a simultaneous estimation together with the TRF while the CRF was fixed. Those computation approaches entail inherent inconsistencies between TRF, EOP, and CRF, also because the input data sets are different. A combined normal equation (NEQ) system, which consists of all the parameters, i.e., TRF, EOP, and CRF, would overcome such an inconsistency. In this paper, we simultaneously estimate TRF, EOP, and CRF from an inter-technique combined NEQ using the latest GNSS, VLBI, and SLR data (2005–2015). The results show that the selection of local ties is most critical to the TRF. The combination of pole coordinates is beneficial for the CRF, whereas the combination of $$\varDelta \hbox {UT1}$$ results in clear rotations of the estimated CRF. However, the standard deviations of the EOP and the CRF improve by the inter-technique combination which indicates the benefits of a common estimation of all parameters. It became evident that the common determination of TRF, EOP, and CRF systematically influences future ICRF computations at the level of several $$\upmu $$ as. Moreover, the CRF is influenced by up to $$50~\upmu $$ as if the station coordinates and EOP are dominated by the satellite techniques.

Beside the estimation of station coordinates and the Earth’s gravity field, laser ranging observations to near-Earth satellites can be used to determine the rotation of the Earth. One parameter of this rotation is ΔLOD (excess Length Of Day) which describes the excess revolution time of the Earth w.r.t. 86,400 s. Due to correlations among the different parameter groups, it is difficult to obtain reliable estimates for all parameters. In the official ΔLOD products of the International Earth Rotation and Reference Systems Service (IERS), the ΔLOD information determined from laser ranging observations is excluded from the processing. In this paper, we study the existing correlations between ΔLOD, the orbital node Ω, the even zonal gravity field coefficients, cross-track empirical accelerations and relativistic accelerations caused by the Lense–Thirring and deSitter effect in detail using first order Gaussian perturbation equations. We found discrepancies due to different a priories by using different gravity field models of up to 1.0ms for polar orbits at an altitude of 500 km and up to 40.0ms, if the gravity field coefficients are estimated using only observations to LAGEOS 1. If observations to LAGEOS 2 are included, reliable ΔLOD estimates can be achieved. Nevertheless, an impact of the a priori gravity field even on the multi-satellite ΔLOD estimates can be clearly identified. Furthermore, we investigate the effect of empirical cross-track accelerations and the effect of relativistic accelerations of near-Earth satellites on ΔLOD. A total effect of 0.0088 ms is caused by not modeled Lense–Thirring and deSitter terms. The partial derivatives of these accelerations w.r.t. the position and velocity of the satellite cause very small variations (0.1μs) on ΔLOD.

In preparation of activities planned for the realization of the Global Geodetic Observing System (GGOS), a group of German scientists has carried out a study under the acronym GGOS-D which closely resembles the ideas behind the GGOS initiative. The objective of the GGOS-D project was the investigation of the methodological and information-technological realization of a global geodetic-geophysical observing system and especially the integration and combination of the space geodetic observations. In the course of this project, highly consistent time series of GPS, VLBI, and SLR results were generated based on common state-of-the-art standards for modeling and parameterization. These series were then combined to consistently and accurately compute a Terrestrial Reference Frame (TRF). This TRF was subsequently used as the basis to produce time series of station coordinates, Earth orientation, and troposphere parameters. In this publication, we present results of processing algorithms and strategies for the integration of the space-geodetic observations which had been developed in the project GGOS-D serving as a prototype or a small and limited version of the data handling and processing part of a global geodetic observing system. From a comparison of the GGOS-D terrestrial reference frame results and the ITRF2005, the accuracy of the datum parameters is about 5–7 mm for the positions and 1.0–1.5 mm/year for the rates. The residuals of the station positions are about 3 mm and between 0.5 and 1.0 mm/year for the station velocities. Applying the GGOS-D TRF, the offset of the polar motion time series from GPS and VLBI is reduced to 50 μas (equivalent to 1.5 mm at the Earth’s surface). With respect to troposphere parameter time series, the offset of the estimates of total zenith delays from co-located VLBI and GPS observations for most stations in this study is smaller than 1.5 mm. The combined polar motion components show a significantly better WRMS agreement with the IERS 05C04 series (96.0/96.0 μas) than VLBI (109.0/100.7 μas) or GPS (98.0/99.5 μas) alone. The time series of the estimated parameters have not yet been combined and exploited to the extent that would be possible. However, the results presented here demonstrate that the experiences made by the GGOS-D project are very valuable for similar developments on an international level as part of the GGOS development.

In its function as an ITRS Combination Centre, DGFI is in charge with the computation of an ITRF2008 solution. The computation methodology of DGFI is based on the combination of datum-free normal equations (weekly or session data sets, respectively) of station positions and Earth orientation parameters (EOP) from the geodetic space techniques DORIS, GPS, SLR and VLBI. In this paper we focus on the DORIS part within the ITRF2008 computations. We present results obtained from the analysis of the DORIS time series for station positions, network translation and scale parameters, as well as for the terrestrial pole coordinates. The submissions to ITRF2008 benefit from improved analysis strategies of the seven contributing IDS analysis centres and from a combination of the weekly solutions of station positions and polar motion. The results show an improvement by a factor of two compared to past DORIS data submitted to ITRF2005, which has been evaluated by investigating the repeatabilities of position time series. The DORIS position time series were analysed w.r.t. discontinuities and other non-linear effects such as seasonal variations. About 40 discontinuities have been identified which have been compared with the results of an earlier study. Within the inter-technique combination we focus on the DORIS contribution to the integration of the different space geodetic observations and on a comparison of the geodetic local ties with the space geodetic solutions. Results are given for the 41 co-location sites between DORIS and GPS.

The Bureau of Products and Standards (BPS), the former Bureau for Standards and Conventions supports IAG’s Global Geodetic Observing System (GGOS) in its goals to integrate the three pillars of geodesy: geometry, rotation and gravity field of the Earth and to obtain geodetic products of highest accuracy and consistency. The key objective of the BPS is to ensure the adoption and implementation of common standards and conventions by all IAG components as a fundamental prerequisite for a consistent processing of the different geometric and gravimetric observations. This paper provides the charter of the BPS and gives an overview about the present activities. A major focus of the work is on the compilation of an inventory based on the evaluation of the standards and conventions currently in use by the IAG Services and their contributing analysis centres for the data processing and for the generation of geometric and gravimetric products, such as geodetic reference frames, Earth orientation parameters, gravity field models and satellite orbits. The paper presents some results of this evaluation regarding numerical standards, including time and tide systems and it addresses various aspects related to the geopotential value W0 and to the datum definition of the International Terrestrial Reference System (ITRS).

The combination of tropospheric parameters derived from different space-geodetic techniques has not been of large interest in geodesy so far. However, due to the high correlation between station coordinates and tropospheric parameters, the latter should not be neglected in combinations. This paper deals with the comparison and combination of tropospheric parameters derived from global positioning system (GPS) and very long baseline interferometry (VLBI) observations stemming from a 15-day campaign of continuous VLBI observations in 2002 (CONT02). The observation data of both techniques were processed homogeneously to avoid systematic differences between the solutions. We compared the tropospheric estimates of GPS and VLBI at eight co-location sites and found a very good agreement in the temporal behavior of the tropospheric zenith path delays (ZPD), reflected by correlation factors up to 0.98. Following this, a combination of the tropospheric parameters was performed. We demonstrate that the combination of tropospheric parameters leads to a stabilization of combined station networks. This becomes visible in the improvement of the repeatabilities of the station height components. Furthermore, the potential use of independent data from water vapor radiometers (WVRs) to validate space-technique-derived tropospheric parameters was investigated. Correlation coefficients of 0.95 or better were estimated between the tropospheric parameters of WVR and GPS or VLBI. Additionally, the utility of the tropospheric parameters for validation of local tie vectors was investigated. Both tropospheric zenith delays and tropospheric gradients were found to be very suitable to validate the height component and the horizontal components of the local tie, respectively.

The International DORIS Service (IDS) submitted input data for the most recent realization of the International Terrestrial Reference System (ITRS), the International Terrestrial Reference Frame 2014 (ITRF2014). As one of the ITRS Combination Centers, DGFI-TUM is in charge to analyze and assess the quality of the submitted data and to compute a combined global TRF solution (called DTRF2014) using observations of the four geodetic space techniques GNSS, VLBI, SLR and DORIS. The combination methodology used at DGFI-TUM is based on the combination of datum-free normal equations. Together with station coordinates and velocities, terrestrial pole coordinates are estimated in one common adjustment. The paper presents the analysis results of the most recent DORIS submission IDS-d09 and evaluates its quality w.r.t. the DTRF2008 (IDS-only) solution. In the most recent version of the analysis, we introduce in total 55 station discontinuities and reduce 15 stations due to a too short time span or too few observations. Time series of weekly IDS solutions are computed and validated w.r.t. DTRF2008. The transformation parameter time series and the station residuals are discussed in detail. Especially the scale parameter time series shows a significant improvement compared to the DTRF2008 input data. The scatter of the x- and y-translation is significantly reduced to 5.7 mm and 7.1 mm compared to 6.6 mm and 8.1 mm for the DTRF2008 (IDS-only) solution. The z-translation time series still shows a high correlation with solar activity. 10% of all station residuals are significantly affected by spectral peaks at draconitic period harmonics of the altimetry satellites Jason and TOPEX/Poseidon and up to 48% of all station residual time series contain significantly determined frequencies with a 14 day period. The multi-year IDS solution is validated w.r.t. DTRF2008 and the consistently estimated terrestrial pole coordinates are analyzed and compared to IERS 08 C04. The x-pole spectra comprises prominent peaks at various draconitic frequencies.

Recent solutions of the terrestrial reference frame such as ITRF2000 are combined from multi-year data sets that contain station positions at a reference epoch and constant velocities. Analysis of time series of station positions of the geodetic space techniques SLR, GPS, VLBI and DORIS show, however, that these techniques allow to detect variations in station position series with up to a few millimetre accuracy. Therefore, the underlying reference frame needs to assure the same accuracy. In this paper we analyse systematic effects in station position and transformation parameter time series that need to be taken into account for future TRF realisations. These are mainly annual signals that show up as common variations of the global networks as well as local effects on individual stations. These annual signals differ significantly from technique to technique for some co-location sites. Apart from periodic signals the time series show discontinuities (e.g. due to earthquakes or instrumentation changes) and periods of non-linear motion (e.g. post-seismic relaxation). We compute TRF technique solutions of five years of epoch normal equations, which allows to adapt the parameterisation in order to account for the effects mentioned above. The accuracy of the technique-specific solutions is evaluated by comparing the results at co-location sites. For this purpose, we transform the VLBI, SLR and DORIS solutions to the GPS solution by using the measured local ties between GPS and the other techniques.

On the basis of LAGEOS-1 and LAGEOS-2 data we computed a 10-years (1990–2000) solution for SLR station positions and velocities. The paper describes the data processing with the DGFI software package DOGS. We present results for station coordinates and their time variation for 41 stations of the global SLR network, and discuss the stability and time evolution of the SLR reference frame established in the same way. We applied different methods to assess the quality and consistency of the SLR results. The results presented in this paper include: (1) a time series of weekly estimated station coordinates; (2) a comparison of a 10-year LAGEOS-1 and LAGEOS-2 solution; (3) a comparison of 2.5-year solutions with the combined 10-year solution to assess the internal stability and the time evolution of the SLR reference frame; (4) a comparison of the SLR reference frame with ITRF97; and (5) a comparison of SLR station velocities with those of ITRF97 and NNR NUVEL-1A.

As early as the 15th century Swedes noticed that rocks in their harbors were slowly rising out of the sea [Ekman, 1991]. These local observations were not sufficient to distinguish whether the rocks were rising or the sea level falling. Later, it was realized that Fennoscandia was still rebounding from the last Ice Age. This historical observation is still relevant today. How can you know whether a point on the Earth's surface is slowly moving up, down, or horizontally? One must relate local measurements to a stable and accurate reference frame, one whose scale is much larger than the problem at hand. We remain concerned with sea-level variations, but present-day studies recognize that change must be measured from a global point of view and with respect to a globally well-defined reference frame. Thus, the regional and national geodetic datums developed over the past 200 years are inappropriate for studying global-level problems.

Repeated GEODYSSEA-GPS measurements and additional GPS data from the IGS and APRGP97/98 constrain the motion of SE-Asia within a global reference frame. Sundaland i.e. Indochina as well as the western and central part of Indonesia, together with South-China, constitute an apparently stable tectonic block that is decoupled from Eurasia. In the ITRF97 this block moves to the east about an Euler pole approximating that of Eurasia, but with a velocity that is one third higher than the eastward directed movement of Eurasia. With respect to India and Australia the Sundaland-South China block is moving due south. This suggests that a) Sundaland-South China are moving coherently to the East along the boundaries studied and b) the eastward motion of India is compensated by the eastward motion of Sundaland-South China. The current rather homogeneous kinematic behaviour of Sundaland-South China that differs in rate (no more than 5 mm) rather than direction from the movement of N-China differs from the kinematics proposed by different modelling approaches throughout the literature. The data help to constrain locations and behaviour of the active fault zones and give information on the interplate and intraplate deformation in the area.

This paper presents the final geodetic results of the GEODYSSEA project. The GPS data from a 42 station network observed during two field campaigns (1994/1996) were analyzed by four groups using different software packages and analysis strategies. The precision of both campaign coordinate solutions was found to be 4–7 mm for the horizontal, and 1 cm for the vertical component. The campaign solutions were merged into one unique solution, which was accurately mapped into the ITRF-96 reference frame. The global accuracy of this solution with respect to ITRF-96 is ±1 cm, while the resolution of the relative horizontal velocities is estimated to be at the level of 2–3 mm/yr. This solution was used as the basis for all scientific interpretations, which are published in separate papers. The velocity estimates of a part of the network provided the first direct measurement of a relative motion of the Sundaland block with respect to Eurasian plate.

A new realization of the International Terrestrial System was computed at the ITRS Combination Centre at DGFI as a contribution to ITRF2008. The solution is labelled DTRF2008. In the same way as in the DGFI computation for ITRF2005 it is based on either normal equation systems or estimated parameters derived from VLBI, SLR, GPS and DORIS observations by weekly or session-wise processing. The parameter space of the ITRS realization comprises station positions and velocities and daily resolved Earth Orientation Parameters (EOP), whereby for the first time also nutation parameters are included. The advantage of starting from time series of input data is that the temporal behaviour of geophysical parameters can be investigated to decide whether the parameters can contribute to the datum realization of the ITRF. In the same way, a standardized analysis of station position time series can be performed to detect and remove discontinuities. The advantage of including EOP in the ITRS realization is twofold: (1) the combination of the coordinates of the terrestrial pole—estimated from all contributing techniques—links the technique networks in two components of the orientation, leading to an improvement of consistency of the Terrestrial Reference Frame (TRF) and (2) in their capacity as parameters common to all techniques, the terrestrial pole coordinates enhance the selection of local ties as they provide a measure for the consistency of the combined frame. The computation strategy of DGFI is based on the combination of normal equation systems while at the ITRS Combination Centre at IGN solutions are combined. The two independent ITRS realizations provide the possibility to assess the accuracy of ITRF by comparison of the two frames. The accuracy evaluation was done separately for the datum parameters (origin, orientation and scale) and the network geometry. The accuracy of the datum parameters, assessed from the comparison of DTRF2008 and ITRF2008, is between 2–5 mm and 0.1–0.8 mm/year depending on the technique. The network geometry (station positions and velocities) agrees within 3.2 mm and 1.0 mm/year. A comparison of DTRF2008 and ITRF2005 provides similar results for the datum parameters, but there are larger differences for the network geometry. The internal accuracy of DTRF2008—that means the level of conservation of datum information and network geometry within the combination—was derived from comparisons with the technique-only multi-year solutions. From this an internal accuracy of 0.32 mm for the VLBI up to 3.3 mm for the DORIS part of the network is found. The internal accuracy of velocities ranges from 0.05 mm/year for VLBI to 0.83 mm/year for DORIS. The internal consistency of DTRF2008 for orientation can be derived from the analysis of the terrestrial pole coordinates. It is estimated at 1.5–2.5 mm for the GPS, VLBI and SLR parts of the network. The consistency of these three and the DORIS network part is within 6.5 mm.

The CONT02 campaign is of great interest for studies combining very long baseline interferometry (VLBI) with other space-geodetic techniques, because of the continuously available VLBI observations over 2 weeks in October 2002 from a homogeneous network. Especially, the combination with the Global Positioning System (GPS) offers a broad spectrum of common parameters. We combined station coordinates, Earth orientation parameters (EOPs) and troposphere parameters consistently in one solution using technique- specific datum-free normal equation systems. In this paper, we focus on the analyses concerning the EOPs, whereas the comparison and combination of the troposphere parameters and station coordinates are covered in a companion paper in Journal of Geodesy. In order to demonstrate the potential of the VLBI and GPS space-geodetic techniques, we chose a sub-daily resolution for polar motion (PM) and universal time (UT). A consequence of this solution set-up is the presence of a one-to-one correlation between the nutation angles and a retrograde diurnal signal in PM. The Bernese GPS Software used for the combination provides a constraining approach to handle this singularity. Simulation studies involving both nutation offsets and rates helped to get a deeper understanding of this singularity. With a rigorous combination of UT1–UTC and length of day (LOD) from VLBI and GPS, we showed that such a combination works very well and does not suffer from the systematic effects present in the GPS-derived LOD values. By means of wavelet analyses and the formal errors of the estimates, we explain this important result. The same holds for the combination of nutation offsets and rates. The local geodetic ties between GPS and VLBI antennas play an essential role within the inter-technique combination. Several studies already revealed non-negligible discrepancies between the terrestrial measurements and the space-geodetic solutions. We demonstrate to what extent these discrepancies propagate into the combined EOP solution.

This paper focusses on some relevant aspects when proceeding towards a rigourous combination of space geodetic observations that are addressed by the IERS Combination Research Centers at DGFI and FESG in the frame of the IERSGEOTECHNOLOGIEN project. These are in particular investigations related to the datum realization for the space geodetic solutions, the analysis and combination of SLR and VLBI data, and research activities within the IERS SINEX Combination Campaign and the IERS Combination Pilot Project.

Results from repeated measurements across a 90-sites global positioning system network in Central Asia provide direct evidence of current high rates of tectonic deformation far north of the India–Eurasia suture zone. The data help to quantify both the partitioning of deformation within the seismically active Tien Shan and Northern Pamirs, as well as the ongoing rotation of virtually undeformed blocks such as the Tarim with respect to stable Eurasia. The NNW to SSE shortening rates derived from the computations reach values of 23±3 mm yr −1 over the ranges studied, suggesting that regional deformation rates have increased considerably within the study area since the onset of Cenozoic shortening 20–25 Myr ago.

With the advent of global positioning system (GPS) technology and its applications to high precision geodesy, earth scientists have gained an unprecedented opportunity to study the kinematics and dynamics of present-day deformation processes along plate boundary zones. However, until now our knowledge of the deformation processes associated with the Andean subduction along the western coast of South America has been limited. Here we present first estimates of present-day crustal deformation rates in the central and southern sections of the Andes, between latitudes 22‡S and 42‡S. We find that the deformation in the central section of our study area is dominated by the interseismic phase of an earthquake deformation cycle, caused by 100% coupling of the thrust interface between the subducting Nazca and the overriding South America plates. The estimated depth of coupling is not uniform along strike: north of 30‡S it is V33 km deep, while south of 35‡S it reaches 50 km depth. In addition, we observed postseismic relaxation effects in the northern part of our network in the area of the 1995 Mw8.0 Antofagasta earthquake. South of 38‡S, we detected a similar deformation pattern as in the Antofagasta area which we attribute to postseismic relaxation effects of the 1960 Mw9.5 Valdivia earthquake. fl 2001 Elsevier Science B.V. All rights reserved.

GPS data from four sites in the Nazca Plate (Easter Island, Galapagos, Robinson Crusoe and San Felix Islands) and from five sites in the stable core of the South American Plate enabled us to estimate the Euler vector of the Nazca Plate with respect to South America. The observed velocities of Easter Island (6.6 cm/yr at 102.3< degrees >), Galapagos (5.1 cm/yr at 90.0< degrees >), Robinson Crusoe (6.6 cm/yr at 80.1< degrees >) and San Felix (6.0 cm/yr at 82.1< degrees >) are significantly slower than the global plate model NUVEL-1A velocities for those four sites. Our estimated Euler pole is located at 48.8< degrees >N, 91.7< degrees >W with a rate of 0.59< degrees >/m.y. The NUVEL-1A and earlier space-geodetic studies give rotation rates that are 20% faster.

In cooperation with various partners in Europe, North America and in the host countries, GFZ Potsdam has established and repeatedly observed three major GPS networks: in South America the SAGA network, in Central Asia the CATS- and in South-East Asia the GEODYSSEA-network.

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.

Prior to the IGS 92 Campaign, the GeoForschungsZentrum Potsdam (GFZ) and the Forschungsanstalt f. Luft- und Raumfahrt (DLR) made all necessary software and hardware preparations to take part in the campaign as an analysis center. This paper describes some characteristics of the processing software, focuses on the two problem areas of solar radiation and eclipses and gives some first results from the IGS campaign analysis: GPS orbit ephemerides quality, stations' and satellites' clock parameter precisions and pole position uncertainties.

In the framework of the GEODYnamics of South and South-East Asia (GEODYSSEA) project a network of 42 stations was observed by GPS during two field campaigns in 1994 and 1996. BKG and GFZ realized a third observation of the complete network in 1998. The data was analyzed independently by two analysis centers and a precision of the coordinate solutions was found to be 4–7 mm for the horizontal, and 10 mm for the vertical component. Subsequently, these campaign solutions were merged into one unique solution, which was accurately mapped into the International Terrestrial Reference Frame of 1997 (ITRF97). The global accuracy of this solution with respect to ITRF97 is of the order of 10 mm, while the resolution of the relative horizontal velocities is estimated to be at the level of 2–3 mm/yr. Comparison of the new solution with the previously published GEODYSSEA solution indicates, that improved results for the motion of Sundaland, South China and the overall deformation in the area could be found. Improvements are due to the increased time span and due to a better connection to and the advances in the ITRF reference frame. The new set of coordinates and velocities is used as the basis for scientific interpretations, which have been and will be published in separate papers.