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We assess the consistency of sea-level variability derived from tide-gauge (TG) and satellite radar altimeter (ALT) data acquired along the coasts of the Mediterranean Sea. For a coherent comparison between these techniques, we use GNSS observations to characterize the local vertical land movement embedded in TG records, but not affecting ALT data. We first investigate the performance of CMEMS, a gridded altimeter product covering the period 1993–2019. TG and GNSS series are not required to cover the whole altimeter period. The inter-technique comparison reveals good agreement at annual and semi-annual scales, but also the occasional occurrence of nonlinear discrepancies impacting trend estimation. Large-scale patterns of variability are observed in the Ionian region and along the continental shores from the Alboran to the Adriatic Sea. The estimates of linear trends based on TG + GNSS or CMEMS observations are found consistent within 1σ at 27/45 sites, with the best agreement in the Western Mediterranean and Adriatic Seas. We also consider the X-TRACK/ALES altimeter dataset, provided along the tracks of the Jason missions (2002–2018) and optimized for coastal applications. In this case, we identify only 12 sites suitable for the comparison. The results show that inter-technique consistency is impacted by the length of the series used in the comparison. Optimum agreement between X-TRACK/ALES and TG + GNSS trends is reached at the two sites closer to a satellite track. However, we find sites where X-TRACK/ALES-derived sea-level trends present suspicious along-track variations at < 5 km from the coast, where the corresponding 20 Hz series are incomplete and noisy.

We investigated a large network of permanent GPS stations to identify and analyse common patterns in the series of the GPS height, environmental parameters, and climate indexes.The study is confined to Europe, the Mediterranean, and the North-eastern Atlantic area, where 114 GPS stations were selected from the Nevada Geodetic Laboratory (NGL) archive. The GPS time series were selected on the basis of the completeness and the length of the series.In addition to the GPS height, the parameters analysed in this study are the atmospheric surface pressure (SP), the terrestrial water storage (TWS), and a few climate indexes, such as MEI (Multivariate ENSO Index). The Principal Component Analysis (PCA) is the methodology adopted to extract the main patterns of space/time variability of the parameters.Moreover, the coupled modes of space/time interannual variability between pairs of variables was investigated. The methodology adopted is the Singular Value Decomposition (SVD).Over the study area, main modes of variability in the time series of the GPS height, SP and TWS were identified. For each parameter, the main modes of variability are the first four. In particular, the first mode explains about 30% of the variance for GPS height and TWS and about 46% for SP. The relevant spatial patterns are coherent over the entire study area in all three cases.The SVD analysis of coupled parameters, namely H-AP and H-TWS, shows that most of the common variability is explained by the first 3 modes, which account for almost 80% and 45% of the covariance, respectively.Finally, we investigated the relation between the GPS height and a few climate indexes. Significant correlations, up to 50%, were found between the MEI (Multivariate Enso Index) and about half of the stations in the network.

Geologic studies of preserved stairs-like uplifted marine terraces and continuous GPS data collected in subduction zones provide a unique opportunity to investigate, on different time scales, crustal deformation resulting from upper‐plate extension. The West Crati Fault in Calabria, southern Italy, is a normal fault located within the seismically extending upper plate above the Ionian subduction zone. It is of interest because a thorough comparison of the extension rates inferred from geologic and GPS data has not yet been performed. This E-dipping fault lies in an area where a few historical damaging earthquakes occurred, examples are those in 1184 (M 6.7) and 1638 (M 6.7). Fault slip-rates and earthquake recurrence intervals for the West Crati fault are still subject of debate. We investigated raised marine terraces along the strike of the fault, on its footwall over its tips, located above the Ionian subduction zone, to derive refined uplift rates and study the role that known extensional faults contribute to observed coastal uplift. We also estimated short-term vertical and horizontal movements on the hangingwall of this fault by analyzing the data of 7 permanent GPS stations located along the N-S oriented strike of this fault.Our preliminary results demonstrate that (i) GIS-based elevations of Middle to Late Pleistocene marine terraces, as well as temporally constant uplift rates, vary along the strike of this fault, mapped on its footwall; (ii) rates of short-term vertical movements vary along the strike of this fault on its hangingwall. This confirms active deformation, on different time scales, along the E-dipping West Crati Fault, suggesting that the fault slip-rate governing seismic hazard has also been constant through time. Our preliminary results show the importance of mapping crustal deformation within the upper plate above subduction zones to avoid unreliable interpretations concerning the mechanism responsible for regional uplift.

Summary In Northern Italy, natural subsidence affects the Po and Veneto-Friuli Plains. Anthropogenic activities which started during the 1930s enhanced the natural rates considerably. Information on land lowering can be obtained not only by geodetic or geological data, but also analyzing and comparing sea-level time series of neighboring tide gauges. In the Northern Adriatic, several tide gauge stations were operational before the onset of the anthropogenic activities. We analyzed data spanning the period 1873–1922 from Marina di Ravenna, Venice and Trieste, in Italy. The 1897–1922 data of Pula, Croatia, were also considered for the analysis, but this time series was finally discarded because too short. Trieste, located in a relatively stable area, is characterized by a sea-level rate of 1.21 ± 0.35 mm/yr (1875–1922) that can be assumed to be a reliable estimate of the local sea-level rise during the period of interest. We compared the rate observed at Trieste with those obtained at Marina di Ravenna, 3.09 ± 0.31 mm/yr (1873–1922), and Venice, 2.05 ± 0.22 mm/yr (1873–1922). This comparison shows that the natural subsidence rate decreases from Marina di Ravenna to Venice and Trieste, turning out to be 1.88 ± 0.47 mm/yr and 0.84 ± 0.41 mm/yr at Marina di Ravenna and Venice, respectively.

The City of Venice and the surrounding lagoonal ecosystem are highly vulnerable to variations in relative sea level. In the past ~150 years, this was characterized by a secular linear trend of about 2.5 mm/year resulting from the combined contributions of vertical land movement and sea-level rise. This literature review reassesses and synthesizes the progress achieved in understanding, estimating and predicting the individual contributions to local relative sea level, with focus on the most recent publications. The current best estimate of historical sea-level rise in Venice, based on tide-gauge data after removal of subsidence effects, is 1.23 ± 0.13 mm/year (period from 1872 to 2019). Subsidence thus contributed to about half of the observed relative sea-level rise over the same period. A higher – yet more uncertain – rate of sea-level rise is observed during recent decades, estimated from tide-gauge data to be about 2.76 ± 1.75 mm/year in the period 1993–2019 for the climatic component alone. An unresolved issue is the contrast between the observational capacity of tide gauges and satellite altimetry, with the latter tool not covering the Venice Lagoon. Water mass exchanges through the Gibraltar Strait currently constitute a source of substantial uncertainty for estimating future deviations of the Mediterranean mean sea-level trend from the global-mean value. Subsidence and regional atmospheric and oceanic circulation mechanisms can deviate Venetian relative sea-level trends from the global mean values for several decades. Regional processes will likely continue to determine significant interannual and interdecadal variability of Venetian sea level with magnitude comparable to that observed in the past, as well as non-negligible differential trends. Our estimate of the likely range of mean sea-level rise in Venice by 2100 due to climate change is presently estimated between 11 and 110 centimetres. An improbable yet possible high-end scenario linked to strong ice-sheet melting yields about 170 centimetres of mean sea-level rise in Venice by 2100. Projections of natural and human induced vertical land motions are currently not available, but historical evidence demonstrates that they can produce a significant contribution to the relative sea-level rise in Venice, further increasing the hazard posed by climatically-induced sea-level changes.

Time series of GPS coordinates longer than two decades are now available at many stations around the world. The objective of our study is to investigate large networks of GPS stations to identify and analyze spatially coherent signals present in the coordinate time series and, at the same locations, to identify and analyze common patterns in the series of environmental parameters and climate indexes. The study is confined to Europe and the Mediterranean area, where 107 GPS stations were selected from the Nevada Geodetic Laboratory (NGL) archive on the basis of the completeness and length of the data series. The parameters of interest for this study are the stations height (H), the atmospheric surface pressure (AP), the terrestrial water storage (TWS) and the various climate indexes, such as NAO (North Atlantic Oscillation), AO (Artic Oscillation), SCAND (Scandinavian Index) and MEI (Multivariate ENSO Index). The Empirical Orthogonal Function (EOF) is the methodology adopted to extract the main patterns of space/time variability of these parameters. We also focus on the coupled modes of space/time interannual variability between pairs of variables using the singular value decomposition (SVD) methodology. The coupled variability between all the afore mentioned parameters is investigated. It shall be pointed out that EOF and SVD are mathematical tools providing common modes on the one hand, and statistical correlations between pairs of parameters on the other. Therefore, these methodologies do not allow to directly infer the physical mechanisms responsible for the observed behaviors which should be explained through appropriate modelling. Our study has identified, over Europe and the Mediterranean, main modes of variability in the time series of GPS heights, atmospheric pressure and terrestrial water storage. For example, regarding the station heights, the EOF1 explains about 30% of the variance and the spatial pattern is coherent over the entire study area. The SVD analysis of coupled parameters, namely H-AP, TWS-AP and H-TWS, showed that most of the common variability is explained by the first 3 modes. In particular, 70% for the H-AP, 67% for the TWS-AP and 49% for the H-TWS pair. Moreover, we correlated the stations heights with the NAO, AO, SCAND and MEI indexes to investigate the possible influence of climate variability on the height behavior. To do so, the stations heights were represented using the first three EOFs to reduce the potential effect of local anomalies. More than 30 stations, over the total of 107, show significant correlations up to about 0.3 with the AO and SCAND indexes. The correlation coefficients with MEI turn out to be significant and up to 0.5 for about half of the stations.

Thanks to both technological evolution and analysis improvement in the past decades, space geodesy can now monitor crustal movements of a few millimeters over time opening new prospects for the study of earthquakes. However, fully exploiting the potential of geodetic measurements is subject to their further integration with seismological analysis and requires the development of a multidisciplinary approach. The new joint IAG-IASPEI sub-commission on Seismogeodesy aims to facilitate the cooperation between the geodetic and the seismological communities in order to improve our current understanding of the different processes leading to earthquakes. The new Seismogeodesy sub-commission will focus on both observational challenges and theoretical aspects. Particular effort will be dedicated to identifying gaps of knowledge and opportunity for progress. Specifically, the sub-commission will:* actively encourage the cooperation between all geoscientists studying the plate boundary deformation zones, by promoting the exploitation of synergies between different fields;* work to reinforce collocated and integrated geodetic and seismological monitoring of seismically active areas, inland and off-shore by increasing and/or developing infrastructures dedicated to broadband observations from the seismic wave band to the permanent displacement;* be a reference group for the integration of the most advanced geodetic and seismological techniques by developing consistent methodologies for data reduction, analysis, integration, and interpretation;* act as a forum for discussion and scientific support for international geoscientists investigating the kinematics and mechanics of the plate boundary deformation zone;* promote the use of standard procedures for geodetic data acquisition, quality evaluation, and processing, particularly GNSS data and InSAR data;* promote earthquake geodesy, the study of seismically active regions with large earthquake potential, and geodetic application to early warning system of earthquakes and tsunamis for hazard mitigation;* promote the role of geodesy in tectonic studies for understanding the seismic cycle, transient and instantaneous deformation, and creeping versus seismic slip on faults.* facilitate and stimulate the integrated exploitation of large data sets, using Machine Learning and Data Mining* support the organization of periodic workshops, meetings, summer schools with special emphasis on interdisciplinary research and interpretation and modeling issues* help to the emergence of a new generation of researchers in Seismogeodesy worldwideWe invite any researcher interested in Seismogeodesy to join us and have a fruitful discussion in front of our poster.

The oldest tide gauge observations date back to the 18th century. Although, globally, they are available in limited number, these centuries-old sea level time series are the only data records providing information on the long-period rates of change of the mean ocean surface. Knowledge of the past sea level behavior can contribute key insights to the understanding of climate change impacts. We highlight the greatest importance of monitoring sea-level changes at all spatial scales, from global to local, using terrestrial and space techniques and outline the physical processes, natural and man-induced, responsible for such changes. In general, tide gauge data are made available through different archiving facilities serving both international and national developments. Tide gauges measure local sea-level relative to a benchmark on land, hence, correctly interpreting these observations is challenging since it demands, among other requirements, a proper knowledge of vertical land motions at the stations. In general, it is not easy to find well documented historical data; moreover, benchmarks were not frequently leveled. For more than two decades, space geodetic techniques, such as GNSS (Global Navigation Satellite System) and InSAR (Interferometric Synthetic Aperture Radar), have provided the opportunity to accurately position points in the surroundings of tide gauge sites, potentially giving rise to a large amount of information. However, despite the availability of these techniques, the evolution of the international efforts aiming at realizing consistent observational infrastructures for sea level networks is undergoing only a slow development. In the Mediterranean area, there are a few centennial tide gauge records. Our study focuses on the time series of Alicante, in Spain, Marseille, in France, Genoa, Marina di Ravenna (formerly Porto Corsini), Venice and Trieste, in Italy. After briefly reviewing the gauge types presently in use for sea level measurements, a comprehensive historical description is given for each time series, which may assist understanding an assessment of the problems these stations have experienced over more than one century of operations. Two Italian stations, Marina di Ravenna and Venice, are affected by both natural and anthropogenic subsidence, the latter was particularly intense during a few decades in the 20th century because of ground fluid withdrawal. For these two stations, we have retrieved leveling data of benchmarks close to the tide gauges from the end of the 19th century and, for the last couple of decades, we have evaluated GPS and InSAR heights in close proximity to the stations. The GPS (Global Positioning System) and SAR results were carefully compared. Modeling of the long-period non-linear behavior of subsidence was successfully accomplished by using an ensemble of leveling, GPS and SAR data. After removing the vertical land motions in Venice and Marina di Ravenna, and the inverted barometer effect at all the sites, the linear long period sea-level rates were estimated. The results are in excellent agreement ranging between + 1.2 and + 1.3 mm/year for the overall period from the last decades of the 19th century till 2012. The associated errors, computed by accounting for serial autocorrelation, are of the order of 0.2–0.3 mm/year for all stations, except Alicante, for which the error turns out to be 0.5 mm/year. Our estimated rates for the northern Mediterranean, a relatively small regional sea, are slightly lower than the global mean rate, + 1.7 ± 0.2 mm/year, recently published in the IPCC AR5 (Intergovernmental Panel on Climate Change 5th Assessment Report) (Church et al., 2013), but close enough, if uncertainties are taken into account. It is known that Mediterranean stations had always had lower trends than the global-average ones. Our regional results, however, are in close agreement with the global mean rate, + 1.2 mm/year, published by Hay et al. (2015) which is currently being discussed by the oceanographic community (see, for example, Hamlington and Thompson, 2015). The six time series were also analyzed by means of the EOF (Empirical Orthogonal Functions) technique over the 1934–2012 common period. As a result, about 50% of the total variance is explained by the first mode, which is characterized by a coherent behavior of the six stations.

The historical data corresponding to the period 1873–1922 of the Porto Corsini (northern Adriatic, Italy) tide gauge have been retrieved from the archive of the Italian Istituto Geografico Militare, in Florence ( http://www.igmi.org ). The data consist of daily high and low waters, which were recorded in six handwritten volumes. The 1873–1896 observations were, until now, totally unknown since they were never published, while, for the remaining years, only monthly mean values were available. We digitized and quality controlled the rescued data. Searching in different archives, we also found detailed information on the three sites occupied by the tide gauge within the Porto Corsini/Marina di Ravenna harbor. In addition, the rescue of the leveling data and of the datum definition made it possible to realize a homogeneous time series of monthly mean sea-level values, which now spans 144 years. Sea-level time series exceeding a century are rare, and they are most important because they provide key information for studying climate change-related processes. The Porto Corsini/Marina di Ravenna area is affected by natural subsidence, much enhanced by anthropogenic activities during the period 1940–1980, in particular. Using leveling, GPS and InSAR data we have modeled the subsidence behavior over the 1873–2016 period. After removing the subsidence from the series of monthly mean values, we estimated a long-period linear sea-level rise of + 1.25 ± 0.16 mm/year.

The realization of the international terrestrial reference frame (ITRF) is currently based on the data provided by four space geodetic techniques. The accuracy of the different technique-dependent materializations of the frame physical parameters (origin and scale) varies according to the nature of the relevant observables and to the impact of technique-specific errors. A reliable computation of the ITRF requires combining the different inputs, so that the strengths of each technique can compensate for the weaknesses of the others. This combination, however, can only be performed providing some additional information which allows tying together the independent technique networks. At present, the links used for that purpose are topometric surveys (local/terrestrial ties) available at ITRF sites hosting instruments of different techniques. In principle, a possible alternative could be offered by spacecrafts accommodating the positioning payloads of multiple geodetic techniques realizing their co-location in orbit (space ties). In this paper, the GNSS–SLR space ties on-board GPS and GLONASS satellites are thoroughly examined in the framework of global reference frame computations. The investigation focuses on the quality of the realized physical frame parameters. According to the achieved results, the space ties on-board GNSS satellites cannot, at present, substitute terrestrial ties in the computation of the ITRF. The study is completed by a series of synthetic simulations investigating the impact that substantial improvements in the volume and quality of SLR observations to GNSS satellites would have on the precision of the GNSS frame parameters.

Global navigation satellite systems (GNSS) data are a fundamental source of information for achieving a better understanding of geophysical and climate-related phenomena. However, discontinuities in the coordinate time series might be a severe limiting factor for the reliable estimate of long-term trends. A methodological approach has been adapted from Rodionov (Geophys Res Lett 31:L09204, 2004 ; Geophys Res Lett 31:L12707, 2006) and from Rodionov and Overland (J Marine Sci 62:328-332, 2005) to identify both the epoch of occurrence and the magnitude of jumps corrupting GNSS data sets without any a priori information on these quantities. The procedure is based on the Sequential t test Analysis of Regime Shifts (STARS) (Rodionov in Geophys Res Lett 31:L09204, 2004). The method has been tested against a synthetic data set characterized by typical features exhibited by real GNSS time series, such as linear trend, seasonal cycle, jumps, missing epochs and a combination of white and flicker noise. The results show that the offsets identified by the algorithm are split into 48 % of true-positive, 28 % of false-positive and 24 % of false-negative events. The procedure has then been applied to GPS coordinate time series of stations located in the southeastern Po Plain, in Italy. The series span more than 15 years and are affected by offsets of different nature. The methodology proves to be effective, as confirmed by the comparison between the corrected GPS time series and those obtained by other observation techniques. © 2014 Springer-Verlag Berlin Heidelberg.

In this study the integration of Sentinel-1 InSAR (Interferometric Synthetic Aperture Radar) and GPS (Global Positioning System) data was performed to estimate the three components of the ground deformation field due to the Mw 6.0 earthquake occurred on August 24th, 2014, in the Napa Valley, California, USA. The SAR data were acquired by the Sentinel-1 satellite on August 7th and 31st respectively. In addition, the GPS observations acquired during the whole month of August were analyzed. These data were obtained from the Bay Area Regional Deformation Network, the UNAVCO and the Crustal Dynamics Data Information System online archives. The data integration was realized by using a Bayesian statistical approach searching for the optimal estimation of the three deformation components. The experimental results show large displacements caused by the earthquake characterized by a predominantly NW-SE strike-slip fault mechanism., The research has been supported by the “Marco Polo” project by the University of Bologna (UNIBO), the Spanish Ministry of Economy and Competitiveness research project ESP2013-47780-557 C2-1-R and the EU 7th FP MED-SUV project (contract 308665).

WEGENER is originally the acronym for Working Group of European Geoscientists for the Establishment of Networks for Earth-science Research. It was founded in March 1981 in response to an appeal delivered at the Journées Luxembourgeoises de Geodynamique in December 1980 to respond with a coordinated European proposal to a NASA Announcement of Opportunity inviting participation in the Crustal Dynamics and Earthquake Research Program. WEGENER, during the past 32 years, has always kept a close contact with the Agencies and Institutions responsible for the development and maintenance of the global space geodetic networks with the aim to make them aware of the scientific needs and outcomes of the project which might have an influence on the general science policy trends. WEGENER was serving as Inter-commission Project 3.2, between Commission 1 and Commission 3, of the International Association of Geodesy (IAG) until 2012. Since then, WEGENER project has became the Sub-commission 3.5 of IAG commission 3, namely Tectonics and Earthquake Geodesy. In this study, we briefly review the accomplishments of WEGENER as originally conceived and outline and justify the new focus of the WEGENER consortium. The remarkable and rapid evolution of the present state of global geodetic monitoring in regard to the precision of positioning capabilities (and hence deformation) and global coverage, the development of InSAR for monitoring strain with unprecedented spatial resolution, and continuing and planned data from highly precise satellite gravity and altimetry missions, encourage us to shift principal attention from mainly monitoring capabilities by a combination of space and terrestrial geodetic techniques to applying existing observational methodologies to the critical geophysical phenomena that threaten our planet and society. Our new focus includes developing an improved physical basis to mitigate earthquake, tsunami, and volcanic risks, and the effects of natural and anthropogenic climate change (sea level, ice degradation). In addition, expanded applications of space geodesy to atmospheric studies will remain a major focus with emphasis on ionospheric and tropospheric monitoring to support forecasting extreme events. Towards these ends, we will encourage and foster interdisciplinary, integrated initiatives to develop a range of case studies for these critical problems. Geological studies are needed to extend geodetic deformation studies to geologic time scales, and new modeling approaches will facilitate full exploitation of expanding geodetic databases. In light of this new focus, the WEGENER acronym now represents, “World Earthquake GEodesy Network for Environmental Hazard Research”.

The Italian Space Agency is funding 27 scientific projects in the framework of Cosmo/Skymed program (hereafter CSK) . A subset of them are focusing on the improvements of the quality and quantity of information which can be extracted from X-SAR data if integrated with other independent techniques like GPS or SAR imagery in L and C bands. The GPS observations, namely zenith total delays estimated by means of GPS ground stations, could be helpful to estimate the troposphere bias to remove from IN-SAR imagery. Another contribution of GPS could be the improvements of the orbits of Cosmo/SkyMed satellites. In particular the GPS navigation data of the CSK satellites could serve to improve the atmospheric drag models acting on them. The integration of SAR data in L and C bands on the other hand are helpful to investigate land hydrogeology parameters as well as to improve global precipitation observations. The combined use of L, C and X SAR data with different penetration depth could give profiles of land surface properties, especially in forest and snow/ice-packs. For what concern the use of X-SAR imagery for rain precipitation monitoring, particular attention will be paid to its polarimetric properties that we plan to determine aligning the CSK observations with those obtained with ground L and C radars. Anyway the study goals, the approaches proposed, the test sites identified and the external data selected for the development and validation will be described for each project. Particular attention will be paid to single the advantages that the research activities can benefit from the added potentials of CSK system: the more frequent revisiting time and the higher resolution capabilities.

The daily GPS height series of the Medicina station were analyzed for the period July 1996–September 2001. The station is located in the middle Po Plain on fine-grained alluvial deposits. A seasonal oscillation in the order of 18 mm (peak-to-peak amplitude) is present in the data. This crustal deformation has been modeled by including variations in the atmospheric, oceanic and hydrologic mass. The vertical positions can also be affected significantly by soil consolidation. Geotechnical parameters derived by in situ tests and laboratory analyses of the clayey soil collected at Medicina allowed the estimate of the soil settlement relevant to the seasonal oscillation of the surficial water table. Thermal expansion of the geodetic monument has to be taken into account in the case of high-precision vertical positioning. In this work models both for the soil consolidation and the thermal expansion effects are provided. The continuous gravity observations collected at Medicina by means of a superconducting gravimeter also exhibit a marked seasonal oscillation, which has been interpreted as the sum of loading and Newtonian attraction effects, as well as of the contribution due to soil consolidation. Especially the study concerning the soil consolidation effect has allowed a better insight on the seasonal vertical movements occurring at the Medicina station by providing quantitative information on soil behavior due to change of effective pressures. The results can be applied to those stations characterized by similar fine-grained soils and surficial hydrogeology.

In the framework of the European Union SELF II project, a study was developed in order to assess the accuracy with which vertical crustal movements could be determined by means of continuous GPS and gravity observations in a relatively short timespan of a few years. The reliable knowledge of vertical rates at tide gauge stations is necessary to properly interpret sea level variations. For height determinations, continuous GPS and gravity measurements started in mid-1996 at Medicina, in the southern Po Plain. Additionally, continuous GPS observations have also been performed at Porto Corsini, on the Adriatic coast, where a tide gauge station is located which belongs to the Italian tide gauge network, and at a station in Bologna. Negative linear trends, of different magnitude, have been identified at the three stations. The time variability of gravity and GPS heights in relation to variations of several environmental parameters was investigated. A marked seasonal signal has been identified in both data series. It has been interpreted as the sum of different loading and Newtonian attraction effects modeled on the basis of the relevant environmental data series. At Medicina, the comparison between height and gravity series has shown that the seasonal variations are quite comparable both in amplitude and phase. The only remarkable difference between the two data sets is a sudden increase in gravity, in the order of 3 μgal, observed in mid-1997. This has been attributed to mass/density increase associated with uprising of deep-seated salty (connate) waters, likely triggered by local stress field changes. A simple model is proposed to check the feasibility of the suggested mechanism and the magnitude of the relevant gravity anomaly. This study demonstrated, among other aspects, the importance of collecting continuous, high accuracy, multi-parameter data series for an appropriate interpretation of signals related to environmental variability. For sea level fluctuation studies, the need for determining reliable long-term linear trends in station heights has been demonstrated for the Porto Corsini station. The sea level trend estimated by means of the tide gauge data and the GPS vertical crustal rate has been compared with the absolute sea level trend for the Northern Adriatic provided by the Topex–Poseidon satellite altimetry mission. Over the time frame of the satellite altimetry data set, the results provided by the two different measuring approaches agree within the errors of the estimated sea level trends.

During 1996, a Global Positioning System (GPS) receiver and a superconducting gravimeter (SG) were installed at Medicina, Italy, in order to monitor ground deformation and signals related to global/regional processes and local environmental effects. First results provided by this combined observing strategy are presented, by focusing on common patterns as well as on the differences observed in the two time series. A marked annual signal of increasing amplitude, present in both series, is becoming quite recognizable towards the end of 1997. Seasonal loading effects induced by air pressure, the ocean and surficial water table were estimated and modeled for both data sets. For the gravity series, 12-h data of balloon radio sounding launches have been used to estimate the attraction effect of the seasonal vertical density distribution of the air pressure column above the station. Mass effects due to the surficial water table and the ocean were also estimated and accounted for. The comparison between the observed and modeled series, both in the case of GPS heights and gravity, shows a remarkable agreement and provides a convincing explanation for the observed seasonal fluctuations. In the July–September 1997 time frame, a sudden gravity increase occurred. This anomaly is in the order of 3 μGal and is present in the data series after accounting for the seasonal fluctuation. This step-like feature is responsible for most of the estimated positive linear trend present in the data series. The anomalous increase in gravity has been interpreted as due to mass/density variations, likely associated with the uprising of deep-seated waters in relation with local stress field changes. During the second half of 1997, concurrent seismic activity occurred both in the southern Po Valley and in central Italy (Umbria seismic crisis).

The WEGENER group has promoted the development of scientific space-geodetic activities in the Mediterranean and in the European area for the last fifteen years and has contributed to the establishment of geodetic networks designed particularly for earth science research. WEGENER currently has three scientific objectives which are related to plate-boundary processes, sea-level and height changes, and postglacial rebound. In a full exploitation of the space-geodetic techniques, namely SLR, VLBI and GPS, the individual scientific projects do not only pursue these objectives but also contribute to improving and developing the observation techniques as well as the modelling theories. In the past, particularly SLR observations within WEGENER-MEDLAS have provided a fundamental contribution to determine the regional kinematics of the tectonic plates in the Mediterranean with high precision. With GPS, spatially denser site distributions are feasible, and in several WEGENER projects detailed studies of tectonically active areas were possible on the basis of repeated episodic GPS observations. Current projects associated with WEGENER are successful in separating crustal movements and absolute sea-level variations as well as in monitoring postglacial rebound. These tasks require high-precision height determinations, a problem central to all of the present WEGENER activities. In these projects, continuously occupied GPS sites are of increasing importance. Time series of heights observed with continuous GPS can be determined with a few centimeters RMS error thus enabling the reliable estimates of vertical rates over relatively short time intervals. Regional networks of continuous GPS sites are already providing results relevant, for example, for the study of postglacial rebound. The Mediterranean area is an extraordinary natural laboratory for the study of seismotectonic processes, and the wealth of observations acquired in previous WEGENER projects together with new space-geodetic observations will allow the test of geophysical hypotheses linking three-dimensional deformations of the Earth's surface to the dynamics of the Earth's interior. In particular, it is anticipated that WEGENER projects will aim at a test of the slab-detachment hypothesis. The complex investigations on sea-level fluctuations presently carried out at basin scale from the Strait of Gibraltar to the Black Sea make it possible to study the present and recent past interactions of ocean, atmosphere and solid Earth, as well as to develop appropriate models to assess future aspects.

The problem of understanding, assessing and quantifying the causes of sea-level changes has received increased attention during the past several years, in particular in connection with predictions regarding a rise in the global mean sea level due to global warming. The impact aspect of sea-level rise is of particular concern for many coastal areas in densely populated regions of the world. The present availability of space geodetic techniques providing high-accuracy measurements of station positions and of their time variations makes it possible to separate vertical crustal movements and absolute sea-level fluctuations. Gravimetric methods play an important role in the assessment of sea-level variations by providing completely independent measurements of vertical crustal movements. Satellite altimetry now enables the measurement of the spatial variability of sea level. Geological observations can infer former sea levels which are important to understand the present trends. This paper addresses the study of height variations and secular changes in sea level by discussing the most interesting questions and issues, by presenting the current understanding of the phenomena involved, and finally by illustrating the measuring and modeling techniques to be adopted for a comprehensive approach to the problem.

The SELF (SEa Level Fluctuations: geophysical interpretation and environmental impact) project has been developed and realized in the framework of the Environment Programme designed by the Commission of the European Communities. The SELF project was aimed at providing a reliable base for the determination, in the Mediterranean area, of sea-level variations which could then be used as a possible indicator of climate changes and to study the interactions taking place among the ocean, the atmosphere: and the solid Earth. The project has made it possible to define a consistent network of well-established tide gauges encompassing the Mediterranean Basin as far as the Black Sea and to determine to centimeter accuracy the tide gauge benchmark heights in a global well-defined reference system such as the one provided by the SLR/VLBI space techniques. The SELF network constitutes, for the Mediterranean, the necessary prerequisite towards achieving the actual capability to separate vertical crustal movements from true sea-level variations. This has been accomplished through the use of space techniques namely SLR, VLBI and GPS in conjunction with Water Vapor Radiometer observations and absolute gravity measurements. The analysis of the available tide gauge records has shown a high spatial coherence of the annual to multidecadal sea-level variability. Sea-level fluctuations at periods longer than two months were found to be strongly correlated with air pressure. The seasonal cycle was found to be variable in time. Relative sea-level trends determined from records longer than 30 years are less than 1.5 mm/yr. Crustal movement rates as determined from the tide gauge records are in general of the order ± 1.0 mm/yr. The geological observations have shed light on the fact that a marked variability of crustal movements occurs on both the temporal and spatial scale, and it represents a major contribution to relative sea-level fluctuations. This fact has been verified for the selected sector which belongs to one of the more geodynamically active areas of the Central Mediterranean (Aeolian Archipelago). However, this work has shown that, at least at the tide gauges included in the present study, crustal movements are small compared to the decadal to multidecadal sea-level variability but of the same order as the long-term trend in sea level, thus necessitating a careful monitoring if crustal movement is to be separated from the oceanographic contribution to relative sea-level changes.

Eleven years, 1999-2010, of GPS positions of stations located in Europe and the Mediterranean were analyzed together with time series of atmospheric pressure, terrestrial water storage, and surface mass anomalies provided by the GRACE gravity mission. The Empirical Orthogonal Functions (EOF) technique was applied to single variables data series detrended and de-seasoned to identify the main modes of interannual variability in both time and space. For the GPS coordinates, the analysis has revealed the presence of significant interannual fluctuations which were also identified in the time series of the environmental parameters and of the space gravity data. A prominent feature common to the main modes of the time components of all variables is a slope inversion occurring around 2003-2004. During 2003 most of the European continent was affected by a severe drought. A second type of analysis was performed by applying the Singular Value Decomposition (SVD) approach to a few series of variable pairs to study the coupled space/time variability. This mathematical tool is used to examine possible cause-effect physical relationships between variables pairs. The analysis shows, for example, for the atmospheric pressure and the up coordinate that the first two SVDs account for about 97% of the total covariance. The clear anticorrelation observed between the two SVD1 spatial patterns represents the vertical crustal displacements associated with variations in atmospheric pressure. East-West (EW) and North-South (NS) gradients of the environmental parameters and of the GRACE surface mass anomalies were computed and compared to the EOFs of the east and north GPS coordinates respectively. Significant correlations were found, in particular, between the EW atmospheric pressure gradient and the east EOFs and between the GRACE EW and NS gradients and the east and north EOFs respectively. Significant correlations were also identified between the Multivariate ENSO Index (MEI) and the EOFs of GPS coordinates. (C) 2012 Elsevier Ltd. All rights reserved.

Thorough laboratory measurements performed at INFN-LNF (Istituto Nazionale di Fisica Nucleare-Laboratori Nazionali di Frascati), in the framework of the ETRUSCO (Extra Terrestrial Ranging to Unified Constellations) experiment, proved fundamental to characterize retroreflectors for GNSS (Global Navigation Satellite System) satellites. The standard test developed, SCF-Test, was important to outline the weaknesses of past retroreflectors payloads (in use on GPS, GLONASS and GIOVE A/B satellites). For the upcoming deployment of the Galileo constellation ESA requested, in 2010, a full SCF-Test campaign to characterize a prototype retroreflector of the first IOV satellites. We report the results of a standard SCF-Test and the test of a simulated orbit, called GCO (Galileo Critical half-Orbit). The experience gathered with the ETRUSCO experiment was important for the subsequent project, ETRUSCO-2, whose aim is to develop and measure, in a newly built facility, a full size array of retroreflectors to be deployed on GNSS constellations. Here we report preliminary concurrent thermal and optical simulations of a simulated array. A simplified structure of the array was subject to a simulated space environment in a GCO; the resulting temperature distribution inside each retroreflector, was the input of the optical software to determine the variation of the intensity, throughout the orbit, coming back at a ranging station. The goal is to limit as much as possible signal fluctuations with respect to current deployed arrays.

We built a new experimental apparatus (the “Satellite/lunar laser ranging Characterization Facility”, SCF) and created a new test procedure (the SCF-Test) to characterize and model the detailed thermal behavior and the optical performance of cube corner laser retroreflectors in space for industrial and scientific applications. The primary goal of these innovative tools is to provide critical design and diagnostic capabilities for Satellites Laser Ranging (SLR) to Galileo and other GNSS (Global he capability will allow us to optimize the design of GNSS laser retroreflector payloads to maximize ranging efficiency, to improve signal-to-noise conditions in daylight and to provide pre-launch validation of retroreflector performance under laboratory-simulated space conditions. Implementation of new retroreflector designs being studied will help to improve GNSS orbits, which will then increase the accuracy, stability, and distribution of the International Terrestrial Reference Frame (ITRF), to provide better definition of the geocenter (origin) and the scale (length unit). Our key experimental innovation is the concurrent measurement and modeling of the optical Far Field Diffraction Pattern (FFDP) and the temperature distribution of the SLR retroreflector payload under thermal conditions produced with a close-match solar simulator. The apparatus includes infrared cameras for non-invasive thermometry, thermal control and real-time movement of the payload to experimentally simulate satellite orientation on orbit with respect to both solar illumination and laser interrogation beams. These unique capabilities provide experimental validation of the space segment for SLR and Lunar Laser Ranging (LLR). We used the SCF facility and the SCF-Test to perform a comprehensive, non-invasive space characterization of older generation, back-coated retroreflectors of the GIOVE-A and -B (Galileo In-Orbit Validation Elements) and the GPS-35 and -36 designs. First, using a full GPS flight model at laser wavelengths of 532 and 632 nm, we found its “effective optical cross section” in air, under isothermal conditions, to be six times lower than the Retroreflector Standard for GNSS satellites (100 106 m2 at 20,000 km altitude for GPS and 180 106 m2 for Galileo at 23,200 km altitude), issued by the International Laser Ranging Service (ILRS). Under the simulated thermal and space conditions of the SCF, we also showed that in some space configurations the “effective optical cross section” is further reduced, by the thermal degradation of the FFDP. Using the same SCF-Test configuration on an individual GIOVE prototype cube, we measured severe thermal degradation in optical performance, which appears to be caused by the retroreflector metal coating and the nonoptimized thermal conductance of the mounting. Uncoated retroreflectors with proper mounting can minimize thermal degradation and significantly increase the optical performance, and as such, are emerging as the recommended design for modern GNSS satellites. The COMPASS-M1, GLONASS-115 GNSS satellites use uncoated cubes. They provide better efficiency than those on GPS and GIOVE, including better daylight ranging performance. However, these retroreflectors were not characterized in the laboratory under space conditions prior to launch, so we have no basis to evaluate how well they were optimized for future GNSS satellites. SCF-Testing, under a non-disclosure agreement between INFN-LNF and the European Space Agency (ESA), of prototype uncoated cubes for the first four Galileo satellites to be launched (named “IOV”, In-Orbit Validation satellites) is a major step forward. An SCF-Test performed on a LAGEOS (LAser GEOdynamics Satellite) engineering model retroreflector array provided by NASA, showed the good space performance on what is now a reference ILRS payload standard. The IOV and LAGEOS measurements demonstrated the effectiveness of the SCF-Test as an LRA diagnostic, optimization and validatio...

with contributions by the conference participants: P. Axe, A. Belperio, N. Bernier, R. Bingley, M. Bolgov, W. Bosch, A. Braun, C. Cabanes, A. Cazaneve, J. Chen, S. Cloetingh, G. Di Donato, J. Gregory, R. Hohmann, V. Klemes, P. Knudsen, M. Kuhn, R. Lane, G. Liebsch, J. Lowe, O. Mason, F. Mercier, M. Negusini, C. Paniconi, W. Peltier, H. Plag, F. Remy, B. Richter, A. Selivanov, C. Shum, F. Singer, N. Slotsvik, E. Stanev, N. Teferle, D. Thomson, J. Titus, K. Van Onselen, I. Vilibic, G. Woppelmann, J. Zwally

WEGENER is the acronym for Working group of European Geoscientists for the Establishment of Networks for Earth-science Research. At present, WEGENER is the Inter-commission Project 3.2, between Commission 1 and Commission 3, of the International Association of Geodesy (IAG). For almost thirty years, WEGENER has promoted the development of scientific space-geodetic activities in the Mediterranean and European area by supporting international cooperation and by being a Forum for European and all other Earth scientists interested in the Eurasian/African plate boundary zone. In particular, it has contributed to the establishment of geodetic networks designed specifically for Earth science research. The mission of WEGENER is the development of interdisciplinary work for the integration of space and terrestrial techniques in the study of the Eurasian/African plate boundary deformation zone and adjacent areas, including the establishment of an European velocity field. On September 15-18, 2008, WEGENER held its 14th General Assembly in Darmstadt, Germany, with the title “WEGENER: an interdisciplinary approach to Earth science research and modeling”. This special issue of the Journal of Geodynamics compiles a selection of manuscripts resulting from papers presented during this assembly. Today Earth Science research has reached an unprecedented level. The Global Earth observations Systems and the underlying satellite missions, such as the Global Navigation Satellite Systems (GNSS), altimeter satellites both for sea level studies and for radar imaging of surface deformation and, in particular, the gravity field monitoring missions like GRACE and GOCE are contributing each year terabytes of new data allowing to detect and interpret previously unobservable effects. These recent technological and scientific achievements have broadened the scope of WEGENER since a global view on many phenomena and data combination is often necessary for a comprehensive, integrated multi-technique assessment of Earth Science research and modeling. Recent developments and the most significant advances are presented in the manuscript “The Interdisciplinary Role of Space Geodesy – Revisited” by Reiner Rummel who delivered the opening lecture of the assembly. The program of the 14th Assembly of WEGENER was articulated around five major sessions: Current plate motions and inter- and intraplate deformations. Focusing on Europe, the Mediterranean and surrounding regions; Contribution of new Earth observation systems and methodologies; The Global Geodetic Observing System (GGOS) and its regional implementations; Open Session: Geosciences from Northern Africa to Central and Northern Europe; Special Session: The Mediterranean: A geohazards focus area. Classical WEGENER topics were presented in the first session. The unraveling of the tectonic complexity of the region calls for an integrated approach involving observations of crustal and surface deformation. The session on new Earth observation systems and methodologies focused on exploring the benefits of integrating different positioning techniques with other geodetic/geophysical information. The presentations and the selected papers in this volume show the vast emerging capacities of SAR in numerous geo-sciences applications. The regional contributions to GGOS, such as those provided by WEGENER, were discussed to a large extent, since GGOS is the main project in the high-level international geodetic cooperation among agencies, research institutions and individual scientists. The open Session on Geosciences from Northern Africa to Central and Northern Europe dealt with different strategies and techniques to be adopted both in a recent as well as in a mature environment for geodynamical studies. Different perspectives in the application of GNSS networks in the Southern Mediterranean and the Central European Countries were shown that covered both continuous and episodic monitoring of recent deformation...

This work describes a study of GPS heights, gravity and hydrological time series collected by stations located in northeastern Italy. During the last 12 years, changes in the long-term behaviors of the GPS heights and gravity time series are observed. In particular, starting in 2004–2005, a height increase is observed over the whole area. The temporal and spatial variability of these parameters has been studied as well as those of key hydrological variables, namely precipitation, hydrological balance and water table by using the Empirical Orthogonal Functions (EOF) analysis. The coupled variability between the GPS heights and the hydrological balance and precipitation data has been investigated by means of the Singular Value Decomposition (SVD) approach. Significant common patterns in the spatial and temporal variability of these parameters have been recognized. In particular, hydrology-induced variations are clearly observable starting in 2002–2003 in the southern part of the Po Plain for the longest time series, and from 2004–2005 over the whole area. These findings, obtained by means of purely mathematical approaches, are supported by sound physical interpretation suggesting that the climate-related fluctuations in the regional/local hydrological regime are one of the main contributors to the observed variations. A regional scale signal has been identified in the GPS station heights; it is characterized by the opposite behavior of the southern and northern stations in response to the hydrological forcing. At Medicina, in the southern Po Plain, the EOF analysis has shown a marked common signal between the GPS heights and the Superconducting Gravimeter (SG) data both over the long and the short period.

Today, Geodesy is the science of determining the geometry, gravity field, and rotation of the Earth and their evolution in time. Geodesy in increasingly forced not only to "measure" the geokinematics, gravity field, and rotation, but also to "model" these quantities on the basis of mass transport and dynamics. The instruments (or measurement tools) are of crucial importance in geodesy.

The complexity of the Earth system has been discussed in many fundamental documents in recent years. Trying to understand the Earth system and improve our forecast capability step by step are the great challanges of the Earth system science. It is evident that only a joint effort of many scientific disciplines will make it possible to shed more light into the complexity of the Earth system. Despite enormous progress in recent years the uncertainties of predictions are still rather high. A recent analysis of the deeper reason for the limited quality of climate forecasts led to the unanimous cocnlusion that "data are still poor". Data from space will and must play a central role in Earth system research.

[1] The southeastern Po Plain is affected by high natural and anthropogenic subsidence. The area is well suited to test the application of an observational strategy which combines different techniques to extract information on the spatial and temporal variability of the subsidence. The simultaneous availability, at a few stations, of several geodetic observation techniques such as Global Positioning System (GPS), gravity, and Interferometric Synthetic Aperture Radar (InSAR) allows for validation of the individual time series. The combination takes advantage of the complementary strengths of each technique by overcoming the limitations inherent in each single technique alone. The combination of velocities derived from the GPS and gravity data, further complemented by the results of the InSAR Permanent Scatterers technique, allows us to monitor continuously, in space and time, vertical crustal movements. This high-density information is of major importance for understanding the processes responsible for the observed deformation. Here long-term trends were derived, enabling us to map the behavior of subsidence (even exceeding 20 mm/yr) with high spatial resolution in the southeastern Po Plain. The uplifting behavior of the Apennines chain bordering the Po Plain is identified together with a narrow zone separating the contrasting vertical crustal movements.

When setting up GGOS as a project, the IAG Executive Committee asked the GGOS Steering Committee to establish a relationship with the Integrated Global Observing Strategy Partnership (IGOS-P), aiming at the membership of GGOS in IGOS-P. IGOS-P addresses a number of problems and components of Earth observation systems in the frame of specific Themes. Many of the burning questions related to the water cycle, the climate, global change, and geohazards cannot be solved without sufficient knowledge of mass transports throughout the Earth system and the associated dynamics. All these processes affect the three fundamental geodetic quantities, namely the Earth's figure (geometry), its gravity field and its rotation. Consequently, GGOS is an unique contribution to the Global Earth Observing Systems of Systems (GEOSS) in its capability to provide detailed information on the dynamics of the solid Earth and its fluid envelops on all relevant spatial and temporal scales. Therefore, GGOS has proposed an 'Earth System Dynamics' Theme focusing on the definition and implementation of an observing system capable of monitoring the mass transports within the Earth system. The main goal of the suggested Theme is to develop the necessary science basis and to facilitate the implementation of GGOS. It will define the role of GGOS, the underlying strategy and its interface to the other components of EOSS. The Theme will strengthen the linkage between GGOS and its users and will ensure that GGOS be fully integrated in the frame of IGOS. GGOS will be the main driver of this theme, and through the interaction with the other IGOS-P themes, in particular the Ocean, Global Water Cycle, Geohazards, and Coastal Themes, will provide the means for the full exploitation of the geodetic contribution to all the other global observation systems. The Theme will ensure that GGOS meet the user requirements arising both from the other IGOS-P Themes and from the nine societal benefit areas identified by EOS-II.

Over the last few decades, the use of space-born radar altimetry has dramatically improved our knowledge and understanding of the oceans. During this same period, sea level observation with tide gauges has also undergone spectacular changes, both from a technological point of view and in the applicative fields. This article gives a brief history of tidal observation and then explains how this discipline is closely linked both to Geodesy and to Oceanography. The renewed interest in tide gauges is illustrated using some of the author's case studies and results; these reflect how the discipline is complementary to Space Geodesy. Résumé Alors que l’altimétrie radar embarquée sur satellite révolutionne notre connaissance des océans, la marégraphie connaît un essor sans précédent depuis deux décennies, aussi bien dans ses technologies que dans ses applications, et pas seulement pour la validation des mesures effectuées depuis l’espace. Cet article remonte brièvement aux origines de la marégraphie. Il s’attache ensuite à montrer combien cette discipline reste liée à la géodésie autant qu’à l’océanographie. Les raisons du regain d’intérêt qu’elle suscite sont présentées à travers quelques résultats et exemples concrets sur lesquels travaillent les auteurs. Ils illustrent la complémentarité de la marégraphie et de la géodésie spatiale.

[1] The effect of nontidal ocean loading (NTOL) is observed in the height series of four permanent GPS stations in the northern Adriatic. A validation of the ECCO model is performed by comparing model estimates of sea-level anomalies from tide-gauges with TOPEX/ POSEIDON data, and ECCO model estimates of bottom pressure with those derived from temperature and salinity observations.TheamplitudesoftheECCOsea-levelanomaly are found to be 1.4 times smaller than observations; bottom pressure is 2 times smaller. Using a Green’s functions approach to determine elastic deformations, the ECCO ocean bottom pressure is used to estimate surface displacements at the GPS sites. Model results were compared with the height series and with the observed NTOL effect. The height series and the predicted NTOL are highly correlated at all four stations. The analysis performed on superconducting gravimeter data at the Medicina station also shows high correlation. INDEX TERMS: 1208 Geodesy and Gravity: Crustal movements—intraplate (8110); 1223 Geodesy and Gravity: Ocean/Earth/atmosphere interactions (3339); 1243 Geodesy and Gravity: Space geodetic surveys; 1299 Geodesy and Gravity: General or miscellaneous; 1829 Hydrology: Groundwater hydrology. Citation: Zerbini, S., F. Matonti, F. Raicich, B. Richter, and T. van Dam (2004), Observing and assessing nontidal ocean loading using ocean, continuous GPS and gravity data in the Adriatic area, Geophys. Res. Lett., 31 ,L 23609, doi:10.1029/2004GL021185.

Series of gravity recordings at the stations Medicina (Italy) and Wettzell (Germany) are investigated to separate seasonal gravity variations from long-term trends in gravity. The findings are compared to height variations monitored by continuous GPS observations. To study the origin of these variations in height and gravity the environmental parameters at the stations are included in the fact finding. In Medicina, a clear seasonal signal is visible in the gravity and height data series, caused by seasonal fluctuations in the atmosphere including mass redistribution, the ocean, groundwater but also by geo-mechanical effects such as soil consolidation and thermal expansion of the structure supporting the GPS antenna. In Wettzell, no seasonal effect could be clearly identified, and the long-term trend in gravity is mainly caused by ground water variations. The successful combination of height and gravity series with the derived ratio of gravity to height changes indicates that the long-term trends in height and gravity are most likely due to mass changes rather than to tectonic movements.

This work describes measurements and results relevant to crustal movements at the northern border of the Adria plate. The measurements taken into consideration are subsurface observations made with extensometers and tiltmeters and episodic and continuous GPS (CGPS) observations. The subsurface measurements cover a remarkably long period of 34 years, while the episodic GPS campaigns have been performed over a time period of 7 years. The CGPS observations are available since July 1996, and 3.5 years of data have been considered in this work. The main characteristics of each different type of measurement are illustrated, and a first approach is made to compare the results. It is shown that environmental effects are present both in subsurface and surface measurements. Methods to interpret and remove these signals are also proposed. The correlation between crustal deformation and seismic events is investigated, and some examples are presented. The long-term observations are discussed with respect to a well-known model of plate motion. The subsurface crustal long-term observations reveal inversions in the direction of deformation with time scales of 10 or more years, providing important boundary conditions for future geodynamic models of the northern Adria plate. The results show that the comparison between subsurface deformation and CGPS measurements, if made over a sufficiently long period of time, in the order of 10 years, can give important contributions to the understanding of the geodynamical and physical mechanisms related to the earthquake occurrence in this area.

The ongoing geodynamic processes in the Alpine-Mediterranean area are primarily governed by the relative movement of the African lithospheric plate against the Eurasian plate resulting in a predominantly compressional regime along the zone of contact. A counterclockwise rotation of the African plate caused by a higher spreading rate of the floor of the South Atlantic results in a northward directed push leading to lithospheric shortening in the Mediterranean-Alpine belt of about 5 to 10 mm/y. With a NW-SE oriented spreading in the North Atlantic (about 18 mm/y) the zone of contact is under compression thus providing the framework for mountain building processes accompanied by active rifling in preconditioned zones of lithospheric weakness. Although this framework is generally accepted great uncertainty remains with regard to the exact kinematic and dynamic pattern of the large-scale tectonic collision between these two major lithospheric plates. Satellite based geodetic networks have been established in the past 5 years to elucidate the present-day deformation field in the region of the Calabrian and West Hellenic Arcs. Results of the first analysis are being presented in this paper.

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.

The orbit of the Pageos 1 balloon satellite was analyzed for the effects of direct solar and albedo radiation pressure. Anomalous behavior occurred in the orbital acceleration near the end of the 2nd year of the satellite's lifetime which may have resulted from the change in its shape; the shape has become slightly oblate, spinning about a minor axis and precessing about the direction of the sun. The near-earth micrometeoroid particle flux was estimated to be 5 x 10 to the -8th/sq cm/s by analyzing the balloon inflation process with sublimating compounds and the resulting variation of the satellite mass due to the leakage through the holes produced by micrometeoroid bombardment.

In view of the unprecedented increase in population in the developing nations and the apparent concentration of much of this population in urban centers within regions of seismic risk, we recommend the implementation of geodetic networks with a scale and distribution appropriate to characterizing earthquake risk in these nations. Synopsis of resolution adopted by Inter-Union Commission on the Lithosphere (ICL Working Group 1), Belem, Brazil, November 1988.

The accurate and precise implementation of the International Terrestrial Reference Frame (ITRF) is a fundamental requirement for the development of Earth System Sciences. The actual realization of the reference frame, in fact, directly impacts a number of different tasks ranging from precise satellite orbit determination to altimeter calibration, satellite antenna offset assessment for Global Navigation Satellite System (GNSS) and validation of center of mass corrections for spacecrafts carrying on board retro-reflectors for Satellite Laser Ranging (SLR). As a consequence, all the studies investigating motions of the Earth’s surface, including oceans and ice-sheets, strictly depend on the availability of a reliable TRF that is fundamental for geo-referencing the relevant measurements. ITRF realizations must then be periodically updated, in order to account for newly acquired observations and for upgrades in data analysis procedures and/or combination methods. Any innovative computation strategy should ameliorate the realization of the frame physical parameters, namely the origin and the scale, upon which a number of scientific applications critically rely. This work addresses the potential of combining GNSS and SLR observations via their co-location on board GPS/GLONASS satellites. GNSS vehicles equipped with retro-reflector arrays can be tracked by SLR ground stations, which allows determining the spacecraft orbits by means of both optical and microwave signals. In principle, the inter-technique connection so achieved could be exploited for the computation of the ITRF in place of terrestrial ties. These lasts are known to be currently a limiting factor of the frame accuracy because of their inhomogeneous distribution and of their discrepancies with space geodesy estimates due to technique systematic errors. In this study, the strength of the alternative link in orbit has been thoroughly investigated in order to evaluate the performances of the selected space tie approach under the available operational conditions. The analysis focuses on the characterization of the precision, the accuracy and the pertinence of the combined frame parameters., La mise en oeuvre exacte et précise du repère international de référence terrestre (ITRF) est une exigence fondamentale pour le développement des Sciences du Système Terre. La réalisation du référentiel mondial, en fait, concerne directement de nombreux domaines allant de la détermination précise des orbites des satellites, à la calibration des altimètres, à l'évaluation des étalonnages absolus d'antennes satellites pour le Global Navigation Satellite System (GNSS) et la validation des corrections du vecteur du centre de masse pour les véhicules spatiaux portant à bord des rétro-réflecteurs pour la technique de télémétrie laser sur satellite (SLR). En conséquence, toutes les études portant sur les mouvements de la surface de la Terre, y compris les océans et les calottes glaciaires, dépendent étroitement de la disponibilité d'un repère de référence fiable qui est fondamental pour référencer les mesures pertinentes. La réalisation de l'ITRF doit alors être périodiquement mise à jour, afin d'intégrer des nouvelles observations et progrès dans les procédures d'analyse des données et/ou des méthodes de combinaison. Toutes les nouvelles stratégies de calcul doivent viser l'amélioration de la réalisation des paramètres physiques du repère, à savoir l'origine et l'échelle, sur lesquels se fondent de façon critique un grand nombre d'études scientifiques et d'applications civiles. Ce travail se concentre sur le potentiel de combiner les observations GNSS et SLR par leur liens à bord de satellites GPS / GLONASS. En fait, les satellites GNSS équipés de rétro-réflecteurs peuvent être observés par les stations SLR, ce qui permet de déterminer les orbites des satellites à travers les deux signaux : optiques et à micro-ondes. En principe, la connexion inter-technique si réalisée pourrait être exploitée pour le calcul de l'ITRF en place des liens terrestres actuellement utilisés. Ces derniers sont connus pour être aujourd'hui un facteur limitant de la précision du repère en raison de leur distribution inhomogène et de leurs divergences avec les estimations de la géodésie spatiale en conséquence des erreurs systématiques dans les observations. Dans cette étude, la force du lien alternatif en orbite a été soigneusement analysée afin d'évaluer les performances de l'approche de combinaison sélectionnée dans les conditions opérationnelles disponibles. L'investigation porte sur la caractérisation de la précision, de la fiabilité et de la pertinence des paramètres combinés du repère de référence.

In the framework of the WEGENER project (IAG Inter-Commission Project P3.2), and following the directives approved in the last Wegener meeting (Tangier, 2004), a new service dedicated to support geodynamic studies along the Eurasia-Nubia plate boundary is being implemented. GEODAC (GEO-Database and Analysis Center) has three major goals: (1) collect, store and make available geodata to the scientific community, either directly or by providing the necessary links; (2) process and analyze geodetic measurements (in particular GPS observations); (3) promote the use of state-of-art processing methodologies and latest results/solutions by supporting the scientific community, with a special focus on developing countries. The regions selected for the initial phase of implementation of this service were the Iberian Peninsula and North-Western Africa. Existing geodetic and geophysical information is being gathered for archiving and will be made available. Simultaneously, the observations of all available continuously-operating GPS sites in the Iberian Peninsula and Morocco (also including some stations in the Azores, Madeira and Canary Archipelagos, and Europe) are being processed, on a daily basis (with a backward processing extending to January 1996), using the GEODAC facilities. The current status of GEODAC is presented together with the expected improvements in the near future. The interest of individuals and organizations in this center is a major reason towards the full implementation of this project.