Geodetic Reference Frame Research Articles

First astronomical reference meridian in Norway

The first geodetic reference frame in Norway was established by triangulation 1779–1799. In 1785 the formal decision was made to establish the reference meridian in Trondheim. Latitude determinations had already been made in 1782–83 by observing meridian transits of the sun and stars with a geographical circle. Additional instruments were added to equip a small observatory. Time determinations were made with a transit instrument and pendulum clock. Lunar occultations and eclipses of the sun, moon, and Jovian satellites were observed with a Dollond refractor for longitude determination. This activity continued till 1791 when the instruments were transferred to Bergen to establish a control meridian there. We have searched archives in Denmark and Norway to recover original observations, correspondence, and other documents. This allows us to trace the history and to reanalyse observational data to determine statistical uncertainties and gain insight into systematic effects. Observing sites have been identified and allow comparison between historical results and modern GPS measurements.

Global, Regional and National Geodetic Reference Frames for Geodesy and Geodynamics

In July 2003 the International Association of Geodesy (IAG) established the Global Geodetic Observing System (GGOS). The GGOS is integrating the three basic components: geometry, the earth rotation and gravity. The backbone of this integration is the existing global ground network, based on the geodetic space techniques: very long baseline interferometry, satellite laser ranging, global navigation satellite systems and Doppler orbitography and radiopositioning integrated by satellite. These techniques have to operate as one global entity and in one global reference frame. The global reference frame in the GGOS is a realization of the International Terrestrial Reference System (ITRS). The ITRS is a world spatial reference system co-rotating with the Earth in its diurnal motion in the space. The IAG Subcommision for the European Reference Frame (EUREF) in 1991 recommended that the terrestrial reference system for Europe should be coincident with ITRS at the epoch t 0 = 1989.0 and fixed to the stable part of the Eurasian Plate. It was named the European Terrestrial Reference System 89 (ETRS89). On the 2nd of June 2008, the Head Office of Geodesy and Cartography in Poland commenced operating the ASG-EUPOS multifunctional precise satellite positioning system. The ASG-EUPOS network defines the European Terrestrial Reference System ETRS89 in Poland. A close connection between the ASG-EUPOS stations and 15 out of 18 Polish EUREF permanent network stations controls the realization of the ETRS89 on Polish territory. This paper is a review of the global ITRS, as well as a regional and a national geodetic reference systems ETRS89.

Improving GNSS CORS Design: The CORSnet-NSW Adjustable Antenna Mount (CAAM)

Global Navigation Satellite System (GNSS) Continuously Operating Reference Station (CORS) networks are being built and expanded around the world, contributing to the definition and realisation of geodetic reference frames as well as providing reliable and accurate positioning infrastructure for a wide range of applications. Depending on the purpose of the GNSS station, CORS antenna monuments typically vary from concrete pillars anchored to bedrock to masts attached to buildings. An antenna mount is used to connect the GNSS antenna to the monument. In all cases it is desired that the CORS antenna is oriented to True North in order to gain maximum benefit from GNSS antenna modelling. Other requirements generally include the unambiguous definition of the survey mark and Antenna Reference Point (ARP), and a zero or minimal antenna height. This paper introduces the CORSnet-NSW Adjustable Antenna Mount (CAAM), developed by NSW Land and Property Information (LPI) for CORSnet-NSW, LPI’s rapidly growing GNSS CORS network covering the state of New South Wales, Australia. The CAAM was purposely designed to be incorporated into (rather than simply attached to) antenna masts located on buildings or free-standing pole monuments but can also be used for pillar monuments. Being free of removable parts, it is adjustable in order to orient the antenna to True North without introducing an antenna height, thereby allowing clear definition and maximum traceability of the survey mark and the ARP. LPI encourages adoption of the CAAM for use in other GNSS CORS networks.

On the global geodetic observing system: Africa's preparedness and challenges

Space geodetic techniques and satellite missions play a crucial role in the determination and monitoring of geo-kinematics, Earth's rotation and gravity fields. These three pillars of geodesy provide the basis for determining the geodetic reference frames with high accuracy, spatial resolution and temporal stability. Space geodetic techniques have been used for the assessment of geo-hazards, anthropogenic hazards and in the design of early warning systems for hazard and disasters. In general, space geodesy provides products for Earth observation, science and influences many activities (e.g., building and management) in a modern society. In order to further promote the application of space geodetic methods to solving Earth science problems, the Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG) was commissioned as an important geodetic infrastructure that integrates different geodetic techniques (such as Global Navigation Satellite Systems, Very Long Baseline Interferometry, Satellite Laser Ranging, Interferometric Synthetic Aperture Radar and Doppler Orbitography and Radio-positioning Integrated by Satellite), models and analysis techniques for the purpose of ensuring long-term, precise monitoring of geodetic observables vital for monitoring Earth system processes. Since its inception, there has been considerable progress made towards setting up the infrastructure necessary for the establishment of the GGOS database. While the challenges that beleaguer the GGOS are acknowledged (at least at global level), the assessment of an attuned GGOS infrastructure in the African context is necessary, yet lacking. In the present contribution, (a) the African preparedness and response to the observing system is assessed, and (b) the specific scientific and technological challenges of establishing a regional GGOS hub for Africa are reviewed. Currently only South Africa has a fundamental geodetic observatory located at Hartebeesthoek, Pretoria. Other countries in Africa have shown interest to participate in global geodetic activities, in particular through interest in the development of a unified African geodetic reference frame (AFREF). In particular interest has been shown in the proposed African VLBI Network (AVN), which will be partially based on existing ex-telecommunication radio antennas. Several countries are investigating their participation in the AVN, including Kenya, Nigeria and Ghana.

세계측지계 전환에 따른 우리나라 행정구역도상 면적 변화

The national geodetic reference frame of Korea switched to the International Terrestrial Reference Frame (ITRF) in 2003. In order to study the land area changes, we calculated the entire land area of Korea using the administrative boundaries of census data provided by Statistics Korea. The standard transformation procedure by the National Geographic Information Institute (NGII) was followed. The Transverse Mercator (TM) projected coordinates were transformed into the GRS80-based world geodetic reference frame, and the ellipsoidal and the projected areas were calculated. The provinces that range over two projection origins were divided into two polygons and projected using appropriate origins. After the transformation, all boundaries were shifted in the northwestern direction, resulting in a decreased area of (about 0.0013%) on the projected plane. Moving the boundaries into a high latitude area cancels out the effect of the enlarged ellipsoid. In addition, the rate of change shows that a higher-latitude province is more sensitive to the shift of the boundaries. The data by Statistics Korea is significantly different from those of the Ministry of Land, Transport and Maritime Affairs (MLTM), thus it is urgently recommended that the data are integrated and unified.

Signal and noise separation in time series of DORIS station coordinates using wavelet and singular spectrum analysis

The aim of this article is to assess the noise in Doppler Orbitography and Radio-positioning Integrated by Satellite (DORIS) stations coordinate time series in order to better apprehend the spectral content of the non-linear station motion. In the frame of this work, we have used two different approaches to assess the noise, the wavelet transform in the frequency space, and the Singular Spectrum Analysis (SSA) in the phase space. The data used are the weekly solutions of coordinate residuals of 18 stations in STCD format (solution ign09wd01), computed by Institut géographique national/Jet Propulsion Laboratory (IGN, France/JPL, USA) using the GIPSY-OASIS II software package, referred to ITRF2005 and expressed in the local geodetic reference frame. The SSA has properly identified the non-linear trends and the seasonal signals (annual and semi-annual, 120, 59 and 20.3 days) in the analysed time series. The results show that the dominant signal present in the horizontal components (North and East) is mainly of a geophysical nature (plate tectonics) with a variance over more than 90% in most cases, and the remaining noise at 120 days was reduced in the ign09wd01 solution (w.r.t. the previous ign07wd01 solution). Using the wavelet transform method, we also identify, for the CADB station, a vertical discontinuity of 13mm on 3 June 2008. For the noise level determination, both approaches converge to the same results. The standard deviation of the noise is in the range of 7–13, 8–24 and 7–14mm in, respectively, North, East and Vertical components. The noise level is the highest in the east direction, probably related to the high orbit inclination of some DORIS satellites, and is lower in the high latitude stations which provide more observations from the DORIS satellites.

Analysis of position time series of GPS-DORIS co-located stations

We analyse the weekly time series of position residuals of 10 GPS-DORIS (Global Positioning System-Doppler Orbitography and Radiopositioning Integrated by Satellite) co-located stations in order to evaluate the spectral content of the observed nonlinear station motion. We have used the discrete wavelet transform to extract trends and seasonal signals, and the Allan variance to characterise the residual noise which allows to evaluate the positioning stability of stations.The GPS-DORIS co-located time series were produced using the GIPSY/OASIS II software, referred to ITRF2005 and expressed in the local geodetic reference frame. The wavelet analysis has revealed useful nonlinear trends, annual and semi-annual signals contained in the studied time series. For GPS time series, the amplitude of the annual signal is around 1.5 and 2.9mm in the horizontal (North and East) and Vertical components respectively, and the semi-annual signal shows amplitude around 0.8, 1.3 and 2.3mm in the North, East and Vertical components, respectively. For DORIS time series, the annual and semi-annual signals show amplitudes of around 4–6mm in the three components.However, after having removed the trends, annual and semi-annual signals, the slope of the Allan variance graph shows for GPS position time series, a combination of a low flicker noise and dominant white noise in the all three components, while for DORIS time series, the white noise is more frequent in the three components. The noise level, defined by the Allan deviation for the one-year sampling time, is smaller than 3 and 5mm in the three components for GPS and DORIS time series, respectively.

Frame transformation and geoid undulation transfer to GNSS real time positions through the new RTCM 3·1 transformation messages

Radio Technical Commission for Marine Services (RTCM) standardised messages play an important role in real time Global Navigation Satellite Systems (GNSS) applications such as navigation, positioning, civil engineering, surveying, and cartographic or cadastral production. One of the latest agreements on RTCM definitions contains the data fields for real time geodetic reference frame transformation and orthometric heights computation by received geoid undulations via internet protocol. These parameters can be generated dynamically by a GNSS data centre in a network of reference stations, encapsulated in RTCM messages and broadcasted to the rover location so they are centrally administered and the same frame transformations and geoid model are available to every user in the field, obtaining results in a local reference frame in real time. This paper summarises the functionality of the new RTCM 3·1 transformation messages, describes limitations and provides ideas about the possible use for solving specific problems. Test field campaigns are used to describe the real performance and usefulness of these new RTCM 3·1 messages.

Applying Geodesy to Hydrologic Cycle Monitoring

IGCP 565 Workshop 3: Separating Hydrological and Tectonic Signals in Geodetic Observations; Reno, Nevada, 11–13 October 2010; The third International Geoscience Programme (IGCP) 565 workshop took place in Nevada. There were 57 participants from 11 countries representing universities, national laboratories, and government agencies. A series of plenary presentations was followed by breakout sessions addressing topics that included the advances needed to improve modeling algorithms for applications of geodesy to hydrology, working with the Group on Earth Observations (GEO) Water Cycle Community of Practice, and developing a hydrogeodetic data portal. The presentations and discussions underlined the added value in applying geodesy to support hydrologic cycle monitoring and modeling, especially terrestrial water storage. However, before the full benefits of the emerging field of hydrogeodesy become exploitable, there is a need to reduce model uncertainty through validation with point to basin observations; to increase consistency in processing and modeling displacement, gravity variations, and hydrologic processes; and to develop new technologies that merge scale mismatches. Improving accuracy and stability of the geodetic reference frames will extend the applicability of geodesy to hydrologic problems. In tectonically active areas, joint interpretation of tectonic and hydrologic signals is required. Ground truth networks are needed at a higher density and with quality control protocols that ensure accuracy.

The relationship between the Hungarian local and global geodetic reference frames estimated together with local geoid undulations

The theoretical and practical background of the similarity transformation together with the simultaneous estimation of local geoid undulations is presented.The mean features of the traditional network adjustment on the local ellipsoids are summarized and the different Hungarian networks and known geoid solutions are shortly described as the basic data of the test computations.The eigenvalue and eigenvector decomposition revealed that the seven parameter similarity transformation cannot be applied together with the simultaneous local geoid estimation because the rotations about the X and Y axes significantly destroy the condition of the normal equations.However, the replacement of the rotations about the X, Y and Z axes by the rotation about the ellipsoidal normal of the datum point can provide a very well conditioned solution, which takes into account the special role of the datum point of the astro-geodetic network adjustment.Based on the unit weights of the input data an optimal adjustment strategy is demonstrated from a computational point of view, where the five transformation parameters can be estimated together with a very large number of local geoid undulations. The geoid has to be known in the global reference system. The geoid unknowns describe only the relative position of this known geoid with respect to the local reference system.The application of the available and the simultaneously estimated local geoid solutions proved that neglecting local geoid heights has a most significant impact on the scale parameter, while it has no significant effects on the horizontal residuals from the statistical point of view.The small scale difference (1 ppm) and the small rotation (-0.5 arc sec) about the datum point and its ellipsoidal normal of the Hungarian local system with respect to the global GPS system demonstrate the high quality of the traditional measurements as well.

The Problem of Compatibility and Interoperability of Satellite Navigation Systems in Computation of User's Position

The Problem of Compatibility and Interoperability of Satellite Navigation Systems in Computation of User's PositionActually (June 2011) more than 60 operational GPS and GLONASS (Satellite Navigation Systems - SNS), EGNOS, MSAS and WAAS (Satellite Based Augmentation Systems - SBAS) satellites are in orbits transmitting a variety of signals on multiple frequencies. All these satellite signals and different services designed for the users must be compatible and open signals and services should also be interoperable to the maximum extent possible. Interoperability definition addresses signal, system time and geodetic reference frame considerations. The part of compatibility and interoperability of all these systems and additionally several systems under construction as Compass, Galileo, GAGAN, SDCM or QZSS in computation user's position is presented in this paper. Three parameters - signal in space, system time and coordinate reference frame were taken into account in particular.

A back-propagation artificial neural network approach for three-dimensional coordinate transformation

The European Datum 1950 (ED50) of the Turkish national geodetic network (TNGN) and the World Geodetic System 1984 (WGS84) of the Turkish national fundamental GPS network (TNFGN) are in use as geodetic reference frames in Turkey. According to the use of two reference systems, it is necessary to transform the three-dimensional (3D) coordinate data from ED50 to WGS84 or vice versa. The seven-parameter similarity transformation method is frequently used for 3D coordinate transformation in geodesy. In this study, a back propagation artificial neural network (BPANN) that has been more widely applied in engineering among all other neural network models is evaluated as an alternative 3D coordinate transformation method. BPANN is compared with a popular seven-parameter similarity transformation (Molodensky-Badekas) method over a test area, in terms of root mean square error (RMSE). The results indicated that the employment of BPANN transformed 3D coordinates (X, Y, Z) more accurate than Molodensky-Badekas method and can be useful for 3D coordinate transformation between ED50 and WGS84. Key words: 3D coordinate transformation, back propagation artificial neural network, seven-parameter similarity transformation, BPANN, Molodensky-Badekas.

The first privately produced map in Norway with a geodetic reference frame

A map of the district surrounding the largest lake in Norway was published in 1796 by the Topographical Society of Norway. Their members contributed private funds for this unique map and for the publication of the Topographical Journal, containing multidisciplinary descriptions, including environmental, of many regions of the country. The map was produced by lieutenant Niels S Darre, a military surveyor and cartographer, as a private undertaking in his own home district. The geodetic reference point of the map is the church at Vang, the position of which had been determined by repeated astronomical observations by its vicar, Abraham Pihl. He had been trained as an astronomical observer by professor Thomas Bugge at the Round Tower Observatory in Copenhagen. A supporting latitude determination in Lillehammer is also noted on the map, obtained by Maximilian Hell in 1769 on his return from Vardo in Northern Norway to Vienna after a successful observation of the transit of Venus. The observed magnetic deviation from astronomically determined north is given. The map also identifies a marker of the great flood of the river Glomma in 1789, causing environmental and social devastation. We have digitized the map and compared it to a 67 km × 82 km section of a modern, digitized topographical map of Norway, by transforming the UTM projection to a meridian through the church at Vang. While most features coregister acceptably by visual inspections of the old and new maps, we note geometrical deviations of up to 1 km in the locations of western shorelines.

Improved Coordinate Transformation in Dubai Using a New Interpolation Approach of Coordinate Differences

In this study, an improved coordinate transformation method between geodetic reference frames in Dubai, UAE, is investigated. In the first phase of this method, a similarity transformation is performed using a seven-parameter model between points known in the two frames involved in the transformation process. Next, the coordinate differences between the transformed coordinates and their known values in the frame into which they are transformed are computed. A database is then produced containing these coordinate differences. To transform coordinates of other points, their coordinates are initially transformed using the similarity transformation parameters estimated in the first step. Next, the coordinate corrections (as differences) at these points are interpolated using the generated database and added to the initial transformed coordinates. Instead of using the common method of double interpolation from a grid for this purpose, a new method is presented. The method directly interpolates coordinate differences at a required point from coordinate differences of the nearest three known points. These differences in the spatial domain form a triangle. Each triangle is assumed to be a surface. The coordinate difference at the required point is estimated on that surface by geometry. Results from testing show that coordinate transformation at accuracy of 2.1 cm on average was achieved in Dubai, which is better than using only the current traditional similarity transformation. Results also show that the proposed interpolation method has a very good performance.

Geodetic Observations Help Scientists Understand Geohazards and Mitigate Disasters: The GGOS Contribution to GEOSS and an Observing System for Geohazards and Disaster Prevention; Frascati, Italy, 5–6 October 2007

Modern space‐geodetic observations have revolutionized our understanding of geohazards, and these observations have a great potential for further scientific discovery and applications, including early warning.To discuss this, about 50 scientists from the geodetic and geohazards communities took part in a workshop organized by the Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG) as a contribution to the intergovernmental Group on Earth Observations (GEO). Highest‐level representatives of space agencies (European Space Agency, NASA, and Agenzia Spaziale Italiana) emphasized the fundamental importance of the geodetic reference frames for satellite missions and Earth observation. Although high, the present accuracy of these reference frames still is a key limitation in quantifying global change processes such as changes in ice sheets and sea level. Improvements of the reference frame are a pivotal step toward a better understanding of these processes and their impact on society. The representative of GEO identified GGOS as a core element in the Global Earth Observation System of Systems (GEOSS), which aims to integrate Earth observations in order to better serve users in a number of societal benefit areas, including disasters.

A high-resolution model for Eurasia-North America plate kinematics since 20 Ma

SUMMARY We derive the first chronologically detailed model of Eurasia‐North America plate motion since 20 Ma from ship and airplane surveys of the well-expressed magnetic lineations along this slowly spreading plate boundary, including previously unavailable dense Russian magnetic data from the southern Reykjanes Ridge and northern Mid-Atlantic ridge near the Charlie Gibbs fracture zone. From more than 7000 crossings of 21 magnetic anomalies from Anomaly 1n (0.78 Ma) to Anomaly 6n (19.7 Ma), we estimate best-fitting finite rotations and realistic uncertainties. Linear regressions of total opening distances versus their reversal ages at different locations along the plate boundary show that reversal boundaries are shifted systematically outwards from the spreading axis with respect to their idealized locations, with the outward shift ranging from more than 5 km between Iceland and the Charlie Gibbs fracture zone to ∼2 km elsewhere. This outward displacement, which is a consequence of the finite zone of seafloor accretion, degrades estimates of the underlying plate motion and is thus removed for the ensuing kinematic analysis. The corrected plate motion rotations reveal surprising, previously unrecognized features in the relative motions of these two plates. Within the uncertainties, motion was steady from 20 to 8 Ma around a pole that was located ∼600 km north of the present pole, with seafloor spreading rates that changed by no more than 5 per cent (1 mm yr −1 ) along the Reykjanes Ridge during this period. Seafloor spreading rates decreased abruptly by 20 ± 2 per cent at 7.5‐6.5 Ma, coinciding with rapid southward migration of the pole of rotation and a5 ◦ ‐10 ◦ counter-clockwise change in the plate slip direction. Eurasia‐North America plate motion since 6.7 Ma has remained remarkably steady, with an apparently stationary axis of rotation and upper limit of ±2 per cent on any variations in the rate of angular rotation during this period. Based on the good agreement between seismotectonic constraints on present deformation in northeast Asia and directions of motion that are predicted by our 6.7 Ma to present pole, we hypothesize that motion has remained steady to the present and attempt to test this hypothesis with published GPS estimates for Eurasia‐North America motion. We find, however, that GPS estimates that are tied to recent versions of the international geodetic reference frame and rely principally on station velocities from Europe give implausible estimates of recent motion, with the most recently published GPS model predicting convergence along the southern Gakkel Ridge and in the Laptev Sea, where seafloor spreading occurs. An alternative GPS estimate that is not tied to the international terrestrial reference frame and employs GPS station velocities from northeastern Asia is marginally consistent with our 6.7‐0 Ma motion estimate.

Transforming ellipsoidal heights and geoid undulations between different geodetic reference frames

Transforming height information that refers to an ellipsoidal Earth reference model, such as the geometric heights determined from GPS measurements or the geoid undulations obtained by a gravimetric geoid solution, from one geodetic reference frame (GRF) to another is an important task whose proper implementation is crucial for many geodetic, surveying and mapping applications. This paper presents the required methodology to deal with the above problem when we are given the Helmert transformation parameters that link the underlying Cartesian coordinate systems to which an Earth reference ellipsoid is attached. The main emphasis is on the effect of GRF spatial scale differences in coordinate transformations involving reference ellipsoids, for the particular case of heights. Since every three-dimensional Cartesian coordinate system ‘gauges’ an attached ellipsoid according to its own accessible scale, there will exist a supplementary contribution from the scale variation between the involved GRFs on the relative size of their attached reference ellipsoids. Neglecting such a scale-induced indirect effect corrupts the values for the curvilinear geodetic coordinates obtained from a similarity transformation model, and meter-level apparent offsets can be introduced in the transformed heights. The paper explains the above issues in detail and presents the necessary mathematical framework for their treatment.

Transforming ellipsoidal heights and geoid undulations between different geodetic reference frames

Transforming height information that refers to an ellipsoidal Earth reference model, such as the geometric heights determined from GPS measurements or the geoid undulations obtained by a gravimetric geoid solution, from one geodetic reference frame (GRF) to another is an important task whose proper implementation is crucial for many geodetic, surveying and mapping applications. This paper presents the required methodology to deal with the above problem when we are given the Helmert transformation parameters that link the underlying Cartesian coordinate systems to which an Earth reference ellipsoid is attached. The main emphasis is on the effect of GRF spatial scale differences in coordinate transformations involving reference ellipsoids, for the particular case of heights. Since every three-dimensional Cartesian coordinate system ‘gauges’ an attached ellipsoid according to its own accessible scale, there will exist a supplementary contribution from the scale variation between the involved GRFs on the relative size of their attached reference ellipsoids. Neglecting such a scale-induced indirect effect corrupts the values for the curvilinear geodetic coordinates obtained from a similarity transformation model, and meter-level apparent offsets can be introduced in the transformed heights. The paper explains the above issues in detail and presents the necessary mathematical framework for their treatment.

Influence of lithospheric thickness variations on 3‐D crustal velocities due to glacial isostatic adjustment

Predictions of 3‐D crustal velocities driven by glacial isostatic adjustment (GIA) have generally been based on spherically symmetric Earth models. We adopt a finite‐volume formulation to explore the impact of lateral variations in elastic plate strength, including lithospheric thickness changes across the continent‐ocean interface and plate boundary weak zones, on these predictions. Weak zones introduce horizontal rate perturbations with a plate scale coherency and amplitudes reaching 1–2 mm/yr; radial velocity perturbations can be as large, but are geographically isolated to the weak zones (specifically, the North Atlantic Ridge). A discontinuity in ocean‐continent lithospheric thickness significantly impacts rates along continental margins (order 1 mm/yr for radial rates and generally about half this for tangential rates). We conclude that lateral variations in lithospheric strength should be included in future GIA analyzes of space‐geodetic survey results and in assessing the impact of GIA on the stability of geodetic reference frames.

Recent Geodetic Results in the Azores Triple Junction Region

—GPS (Global Positioning System) observations started to be carried out in the Azores region under the scope of the TANGO (TransAtlantic Network for Geodesy and Oceanography) project in 1988. The measurements carried out between 1993 and 2000 (five campaigns) on nine GPS sites (one per island) were reprocessed using two state–of–the-art software packages. Different methodologies were applied to compute each campaign solution and the derived velocity field. The velocity fields, including the motions of two permanent stations, recently installed in the Azores, were computed within the most recent geodetic reference frame, ITRF2000 (International Terrestrial Reference Frame, solution 2000). They are compared with the motions of the stable rigid tectonic plates using as reference DEOS2k, a global tectonic model developed using geodetic data. The relative motions between the Western and Central groups of islands yield to evaluate the opening rate of the Mid-Atlantic Ridge (boundary between the North American plate and the Eurasian and African plates). Concerning the boundary between the Eurasian and African plates, the motion of the TANGO sites in the Central and Eastern groups clearly identifies the transition pattern between those two plates. Two of the sites are considered to be located in the stable part of these plates, whereas the remaining five are within the deformation region of the Eurasia-Africa boundary. The conclusions are analyzed in view of the different deformation models, derived from geodynamic or geophysical data that have been proposed for the region.