While the understanding and modelling of sea level rise (SLR) due to ocean density and mass changes have greatly improved over the past few decades, relative SLR contributions due to vertical land motions (VLMs) remain a major source of uncertainty. It is critical to downscale global and regional sea-level rise to local relative sea-level change as this is what causes coastal impacts and adaptation needs. In particular, land subsidence can strongly exacerbate coastal flood risk, saltwater intrusion, erosion and loss of wetlands and damage to infrastructure. Here, we present the first analysis of pan-European coastal subsidence based on the European Ground Motion Service (EGMS) Ortho product. First, we perform a comparison between EGMS Ortho (Level 3) vertical velocity estimates and GNSS stations vertical velocity. This comparison reveals that the geodetic reference frame used to calibrate EGMS affects the vertical land velocity estimates and needs to be accounted for carefully, especially for the vertical land motions – including sub-millimetric/year velocities – that could affect local SLR estimates. After adjusting the EGMS calibrated product to the International Terrestrial Reference Frame (ITRF2014), we performed an assessment of VLM in European coastal flood plains. Our results show that half of the European area located in coastal flood plain is, on average, experiencing subsidence at a rate stronger than -1 mm/yr. More importantly, we find that urban area and population experience almost a -1 mm/yr subsidence on average (if we discard the uplifting regions due to Glacial Isostatic Adjustment) and for coastal airports and for harbours, the average land motion drops is even larger with -1.5 mm/yr subsidence rate. Finally, while our analysis allows identifying already well-known coastal subsidence hot-spots (e.g. Northern Italian coastal plain, Netherlands), we demonstrate with few examples that EGMS analysis also paves the way toward the identification of subsiding local scale coastal zones that have been ignored so far and for which flooding risk may become a major concern.

Repeated absolute gravity measurements, conducted once or twice per year, have proven valuable for quantifying slow vertical land motion with a precision better than 0.4 mu Gal yr(-1) (1 mu Gal = 10(-8) m s(-2)) after a decade or more. This precision is comparable to vertical velocity estimates derived from continuously operating space-based geodetic techniques such as the Global Navigation Satellite System (GNSS). Furthermore, absolute gravimeters are particularly well suited for long-term studies, as their measurements are based on fundamental length and time standards (laser and atomic clock) and remain independent of terrestrial reference frame realizations, unlike GNSS. Consequently, an absolute gravimeter can return years or even decades later and provide relevant measurements, provided the initial gravity data are well documented and the ground gravity marker remains undisturbed. Following this line of thinking, we have compiled and consistently reprocessed absolute gravity measurements collected between 1998 and 2022 in Brest, on the French Atlantic coast, near its century-long tide gauge station. The entire dataset has been reanalyzed in accordance with international recognized standards for instrumental and modelling corrections. This effort has yielded a 25-year time series of absolute gravity values, which we present and document for future studies, along with details on our reprocessing methodology. We assess the quality of this dataset and evaluate the extent to which the observed linear gravity trend agrees with vertical velocity estimates from the nearby GNSS station co-located with the tide gauge. The gravity data and metadata are made available via the French hydrographic agency Shom portal (https://doi.org/10.17183/DATASET_GRAVI_BREST; Lalancette et al., 2024).

Coastal water monitoring is of increasing importance for applications such as sea level monitoring and urban planning. Currently, traditional tide gauge by radar measurement remains the most widely used method, but it involves placing a sensor close to the water surface, which can lead to its destruction, particularly in hostile maritime environments. Sea level measurement by GNSS-R offers a promising alternative to traditional tide gauge methods by enabling continuous and global sea level measurements (e.g., Larson et al., 2013). It has the significant advantage of limiting the constraints linked to the installation of sensors physically close to the water surface, as a GNSS antenna can be placed away from the coast or on a high structure. Furthermore, this technique takes advantage of the high availability of existing GNSS installations around the globe, which would make it possible to considerably extend the scope of tide gauge measurements on a global scale. Most of the methods used in GNSS-R are based on the analysis of the signal/noise ratio (SNR). They generally use a spectral analysis based on a Lomb-Scargle periodogram and are effective for monitoring mean sea level at the centimeter level (e.g., Larson et al., 2013; Santamaría-Gómez and Watson, 2017; Peng et al., 2021). However, they require a relatively long portion of the SNR series to obtain a precise estimate of the oscillation frequency of the SNR signal. This has the effect of limiting the sampling rate of the measurement series and limits spectral methods to the observation of slow variations in sea level such as the tide. Other approaches use Kalman filtering and show that it is possible to achieve an accuracy of less than 5cm in near real time (e.g., Strandberg, Hobiger and Haas, 2019; Liu et al., 2023). Furthermore, these methods show that it is possible to considerably increase the data sampling rate and thus monitor rapid variations in sea level. This extends the scope of GNSS-R techniques to all applications requiring real-time sea level measurement. We present a novel approach for measuring sea level by analyzing SNR signals with Kalman filtering. This approach relies on the estimation of the oscillation frequency and amplitude of SNR signals using an extended Kalman filter. It has the advantage of providing sea level height estimates at a sampling rate as high as the SNR measurements. The major constraint linked to the method lies essentially in the estimation of the initial phase of the SNR signals, which particularly affects the fit of the SNR signals from setting satellites. GNSS-R measurements were carried out with a sampling frequency of 1 second and compared to those of a tide gauge colocated on the Aix Island ILDX site (France). By combining data from different existing GNSS systems (GPS, GLONASS, Galileo, BDS) and considering all available carriers, we estimate that it is possible to obtain an RMS error of less than 5cm on sites with high tidal ranges (± 6m).

The growing demand for precise, and high-frequency sea level monitoring has foster advances in alternative measurement techniques, with Global Navigation Satellite System Interferometric Reflectometry (GNSS-IR) emerging as a promising approach. This paper presents a novel algorithm for GNSS-IR sea level measurements, using an Extended Kalman Filter (EKF), which continuously estimates reflection heights, and allows sampling frequencies as high as those provided by the GNSS observations. To ensure continuous tracking of reflection heights in dynamic environmental conditions and prevent signal loss, the algorithm leverages multi-constellation GNSS observations and integrates tidal modeling. These features provide redundancy in data, significantly enhancing the robustness of signal tracking and improving the overall accuracy of sea level measurements. The algorithm was validated using data collected from three coastal sites with distinct environmental and hydrodynamic characteristics, Brest (France), Sète (France), and Cedar Key (USA). For each site, at least one year of data was analyzed at a high sampling frequency ranging from 20 to 30 s. Across all sites, we achieved Root Mean Square Differences (RMSD) around 2.5 cm with respect to conventional tide gauges. At Cedar Key, the algorithm successfully resolved a 70 cm storm-induced sea level draw-down during Hurricane Milton in 2024, with an RMSD of 2.0 cm, demonstrating the algorithm ability to accurately capture rapid sea level variations. With its accuracy, flexible resolution, and real-time capability, this cost-effective and scalable approach offers strong potential to fill geographical gaps where classic techniques are challenged.

A distributed Global Navigation Satellite System analysis center, designated SPOTGINS, has been established by several research groups that utilize the GINS software and the CNES-CLS precise products. Despite the heterogeneity in their research objectives, the SPOTGINS members apply the same configuration and metadata. The computed global ambiguity-fixed precise point positioning time series are fully consistent among the members, and are subsequently published as a single product (10.24400/170160/20250414, Santamar & iacute;a-G & oacute;mez et al., 2025). At the time of writing (August 2025), the SPOTGINS dataset includes 5768 daily series from May 2000 to present. This product facilitates a range of research activities, including but not limited to the precise monitoring of the Earth's deformation. A comparison of the SPOTGINS series with published series from the Nevada Geodetic Laboratory solution shows no significant difference in quality.

We present an analysis of coastal subsidence in Europe based on the recent European Ground Motion Service (EGMS) product. First, we compare EGMS products with vertical land velocities from the permanent Global Navigation Satellite System (GNSS) network. Overall, we find a reasonable agreement with a correlation coefficient of 0.94 between the vertical velocities estimates from GNSS stations and the collocated EGMS pixels. However, we obtain systematically more negative values (of up to 1 mm/yr) from EGMS estimates. These deviations could be related to the different reference frame used to calibrate EGMS (ETRF2000) and GNSS (IGS2014). Second, we combine coastal flood plain defined from the new Copernicus digital elevation model (25m resolution) and the EGMS estimates to identify subsiding coastal flood plains at the scale of Europe.

AbstractBeside climate‐change‐induced sea‐level rise (SLR), land subsidence can strongly amplify coastal risk in flood‐prone areas. Mapping and quantifying contemporary vertical land motion (VLM) at continental scales has long been a challenge due to the absence of gridded observational products covering these large domains. Here, we fill this gap by using the new European Ground Motion Service (EGMS) to assess the current state of coastal VLM in Europe. First, we compare the InSAR‐based EGMS Ortho (Level 3) with nearby global navigation satellite systems (GNSS) vertical velocity estimates and show that the geodetic reference frame used to calibrate EGMS strongly influences coastal vertical land velocity estimates at the millimeter per year level and this needs to be considered with caution. After adjusting the EGMS vertical velocity estimates to a more updated and accurate International Terrestrial Reference Frame (ITRF2014), we performed an assessment of VLM in European low elevation coastal flood plains (CFPs). We find that nearly half of the European CFP area is, on average, subsiding at a rate faster than 1 mm/yr. More importantly, we find that urban areas and populations located in the CFP experience a near −1 mm/yr VLM on average (excluding the uplifting Fennoscandia region). For harbors, the average VLM is even larger and increases to −1.5 mm/yr on average. This demonstrates the widespread importance of continental‐scale assessments based on InSAR and GNSS to better identify areas at higher risk from relative SLR due to coastal subsidence.

A new reanalysis of Global Navigation Satellite System (GNSS) data at or near tide gauges worldwide was produced by the University of La Rochelle (ULR) group within the third International GNSS Service (IGS) reprocessing campaign (repro3). The new solution, called ULR-repro3, complies with the IGS standards adopted for repro3, implementing advances in data modelling and corrections since the previous reanalysis campaign and extending the average record length by about 7 years. The results presented here focus on the main products of interest for sea level science: the station position time series and associated velocities on the vertical component at tide gauges. These products are useful to estimate accurate vertical land motion at the coast and supplement data from satellite altimetry or tide gauges for an improved understanding of sea level changes and their impacts along coastal areas. To provide realistic velocity uncertainty estimates, the noise content in the position time series was investigated considering the impact of non-tidal atmospheric loading. Overall, the ULR-repro3 position time series show reduced white noise and power-law amplitudes and lower station velocity uncertainties compared with the previous reanalysis. The products are available via SONEL (https://doi.org/10.26166/sonel_ulr7a; Gravelle et al., 2022).

This chapter introduces the concept of mean sea level and discusses its variability at low frequency time scales (from monthly periods to multidecadal oscillations to millennial changes) in the Mediterranean Sea. It first describes the main techniques for measuring sea level, including instrumental in situ observations from tide gauges and remote observations from altimeters on board of satellites, as well as sea level proxies that are used to reconstruct sea level at millennial time scales. Ancillary geodetic measurements are also described, as these are relevant for coastal monitoring and sea level impacts. Secondly, the chapter focuses on the past evolution of Mediterranean sea level, starting with Holocene changes (ca. 10 kyrs back in time), followed by decadal to centennial sea level trends since the late 19th century, a period coinciding with the instrumental era. Finally, future mean sea level projections in the Mediterranean Sea are provided for the present century and for two climate change scenarios.

Abstract This article presents a curated database of the sea‐level measurements acquired by the network of the five geodetic tide gauges managed over French Polynesia by the Geodesy Observatory of Tahiti from 13 June 2009 to 28 January 2021. A unique feature of this database, with respect to previous databases that host the same raw data, like the Intergovernmental Oceanographic Commission database (IOC, www.ioc‐sealevelmonitoring.org) and the database of ‘Réseaux de référence des observations marégraphiques’ (REFMAR, http://refmar.shom.fr) is that all the time‐tags of the raw measurements (1‐ or 2‐min sampling) have been validated and, if necessary, corrected with a precision of 2 min (time shifts of up to 1 hr can be present in the raw data). Possible outliers have also been flagged, but not removed. In addition, smoothed hourly data are also provided, along with tidal analysis results and estimations of the sea‐level trends for the five tide gauges, with respect to their local geodetic datum. The database, entitled ‘SEA LEVEL collected from TIDE STATIONS in South Pacific Ocean from 2009‐06‐13 to 2021‐01‐28’, can be accessed on the NOAA data servers as ‘NCEI Accession 0244182’ and contains two subsets: The first one is relative to the original sampling rate and the second one is relative to an hourly re‐sampling with harmonic tide models for each tide gauge station.

Understanding drivers of tidal change is a key challenge in predicting coastal floods in the next century. Whilst interactions between tides and atmospheric surges have been studied, the effects of wind and pressure on tides on an annual scale over the Northwestern European shelf have not been investigated. Here, a modelling approach using the shallow water MARS model is carried out to understand and quantify meteorological effects on tidal characteristics. The model setup is validated against the GESLA 3 tide gauge database. Combined and relative influences of wind and pressure are investigated using four modelling scenarios: tide only; tide, wind, and pressure; tide and wind; and tide and pressure. Influences are investigated using a single year of tidal forcing, and across multiple years of meteorological data to examine the sensitivity to temporally changing meteorological conditions. It is found that meteorology influences tidal constituent amplitudes by +/−1 cm, yielding changes that may locally reach 15 cm in the predicted highest tide. Analysis of the shallow water equations show three non-linear interaction terms between tide, wind, and pressure (advective effects, quadratic parameterization of bottom friction, and shallow water effect). Part of the observed changes is shown to arise from meteorologically induced mean sea-level changes.

In this data paper, the sea level time series at Socoa (Saint-Jean-de-Luz, southwestern France) is extended through a data archaeology exercise. We conducted a comprehensive study of national and local archives to catalogue water level records stored in ledgers (handwritten record books) and charts (marigrams from mechanical float gauges), along with other associated documents (metadata). A dedicated effort was undertaken to preserve more than 2000 documents by archiving them in digital formats. Using this large set of rescued documents, the Socoa time series has been extended back to 1875, with more than 58 station-years of additional data. The final time series has hourly sampling, while the raw dataset has a finer sampling frequency of up to 5 min. By analysing precise levelling information, we assessed the continuity of the vertical datum. We also compared the new century-long time series to nearby tide gauge data to ensure its datum consistency. While the overall quality of the time series is generally good, siltation of the stilling well has occasionally affected certain parts of the record. We have successfully identified these impacted periods and flagged the corresponding data as doubtful. This extended high-resolution sea level time series at Socoa, spanning more than 100 years, will be valuable for advancing climate research, particularly when studying the decadal-scale variations in the North Atlantic and investigating the storminess and extreme events along the French Basque coast. The raw digitized water level, the processed dataset, metadata, and the python notebooks used for processing are available at https://doi.org/10.5281/zenodo.7438469 (Khan et al., 2022).

Extreme sea levels are the joint contribution of mean sea level, tide and storm surges. The ClimEx project investigates changes in tide and storm surges over the last century, along the North Atlantic coasts. Concerning the tide, we investigated the long-term changes of the principal tidal component M2, from 1846 to 2018 (Pineau-Guillou et al., 2021). The M2 variations are consistent at all the stations in the North-East Atlantic. The changes started long before the 20th century and are not linear. Regarding the possible causes of the observed changes, the similarity between the North Atlantic Oscillation and M2 variations in the North-East Atlantic suggests a possible influence of the large-scale atmospheric circulation on the tide. A possible underlying mechanism is discussed. Concerning the storm surges, we found a clear shift in the storm surge season at Brest (France), between 1950 and 2000 (Reinert et al., 2021). Extreme storm surge events occurred three weeks earlier (mid-December instead of beginning of January) in the winter 2000 than in the 1950s. Analysis of additional stations in Europe reveals a large-scale process (Roustan et al., 2022). Temporal shifts are positive (later events) in northern Europe, and negative (earlier events) in southern Europe. Such a tendency is similar to the one already reported for European river floods between 1960 and 2010 (Blöschl et al., 2017). References[1] Pineau-Guillou L., Lazure P. and Wöppelmann G. (2021). Large-scale changes of the semidiurnal tide along North Atlantic coasts from 1846 to 2018. Ocean Sci., 17, 17–34. https://doi.org/10.5194/os-17-17-2021[2] Reinert M., Pineau-Guillou L., Raillard N., Chapron B. (2021). Seasonal shift in storm surges at Brest revealed by extreme value analysis. J. Geophys. Res. Oceans, 126, e2021JC017794. https://doi.org/10.1029/2021JC017794[3] Roustan J.-B., Pineau-Guillou L., Chapron B., Raillard N., Reinert M. (2022). Shift of the storm surge season in Europe due to climate variability. Sci. Rep., 12, 8210. https://doi.org/10.1038/s41598-022-12356-5[4] Blöschl G., Hall J., Parajka J., Perdigão R. A. P., Merz B., Arheimer B. et al. (2017). Changing climate shifts timing of European floods. Science, 357(6351), 588–590. https://doi.org/10.1126/science.aan25

While the understanding and modelling of relative sea level rise (SLR) due to ocean density and mass changes have greatly improved over the past few decades, SLR contributions due to vertical ground motions (VGMs) remain a major source of uncertainty. Here, VGMs relate to ground motions that have imprints of a few kilometers, as opposed to broad scale land motion such as Glacial Isostatic Adjustment (GIA). VGMs are caused by processes such as natural resource extraction or the load of anthropogenic infrastructure on recent sediment deposits or natural processes (e.g. sismotectonics, volcanism, landslide), all of which vary in space and time, and can strongly inflate SLR locally.Here, we present a pan-European analysis of relative sea-level changes in Europe considering VGMs based on trends retrieved from the European Ground Motion Service (EGMS). EGMS allows identifying hot spots of robust subsidence along the European coastline such as the north Adriatic coast in Italy, areas such as Palavas (France), Groningen (Netherlands) and many coastal infrastructures such as dikes in La Rochelle (France) where subsidence was not documented earlier. Hence the service delineates where subsidence can have a significant impact to relative sea-level changes in coastal areas. This satisfies a major need from coastal adaptation stakeholders concerned with SLR. EGMS results are complemented and compared with VGMs estimates from permanent Global Navigation Satellite System (GNSS) network stations. The precision of the measurements is discussed: VGMs from GNSS stations derived from 4 different solutions (ULR, NGL, JPL and GFZ) allow accounting for uncertainty in trends estimation techniques. We estimate VGMs residual trends after removing the effect of the GIA from geophysical modelling, but also the effect of contemporary mass redistribution on solid Earth deformation. The results from both GNSS and EGMS suggest that the precision of ground motion velocities can be in the order of a millimetre per year.Overall, these estimates and their uncertainty can be used to produce a new coastal pan-European relative sea-level set of projections that respond to one major user need, namely the identification of areas where sea level rise is amplified by subsidence. However two other user needs remain unachieved: the local attribution of observed sea-level changes to components with a submillimetric per year accuracy and a quantified projection of subsidence, which would at least require subsidence models.

We present the procedure we followed to design an artificial corner reflector (CR) at the Calern site of Cote d'Azur Observatory (France). Although still few in number, such reflectors are an integral part of the Global Geodetic Observing System (GGOS) infrastructure. They can be used as a stable radar target in SAR images to connect local InSAR deformation maps to the global Terrestrial Reference Frame and for SAR absolute determination. During a test phase, the orientation of the CR was changed in order to be aligned toward all possible orbits of Sentinel-1A/1B satellites. On the different SAR images, the CR exhibits a high backscattering signal, and provides a Signal-to-Clutter Ratio larger than 26 dB. Since December 2018, the CR is specifically oriented toward the relative orbit 88. It is clearly detected as a PS in our InSAR analyses and as expected, the standard deviation of displacement measured on the CR is lower than on surrounding PS. A first local survey was performed to locate precisely this CR with respect to the existing geodetic instruments and annual campaigns have been carried out since then to insure its stability over time. (C) 2022 COSPAR. Published by Elsevier B.V. All rights reserved.

Tides are changing on human timescales, and an understanding of reasons for these changes is important for inundation risk assessments and coastal defence planning.Tides are often regarded as astronomically generated phenomena, however recently published literature has investigated changes in tidal characteristics driven by nonastronomical factors.Physical mechanisms of many of these drivers are well understood, however studies assess the impact of a single or limited number of drivers.As such the relative impacts of these drivers are yet unknown.This work aims to investigate the medium to long-term tidal amplitude changes in relation to potential drivers.A statistical approach was developed, and applied to tide gauge data from Brest, Le Conquet, Saint-Malo and Dunkerque.This approach is designed to conduct comparative model fit analysis between competing multivariate linear regression models of tidal characteristics.The five main potential causes of tidal change investigated were: mean sea level, pressure-driven atmospheric storm surge, wind, waves and stratification.Annual mean and standard deviation are considered for storm surge, wind and wave data in order to represent the average value over the year and the intra-annual variability.Models of constituent amplitudes were constructed using every combination of drivers.The best models were selected using the Bayesian Information Criterion, and models displaying a negative R 2 or non-significant correlation were discarded.The results suggest the inverse barometer effect (a proxy of atmospheric storm surges) to be among the most commonly occurring drivers in models of tidal amplitudes for all 4 sites.These preliminary results will be further investigated using a hydrodynamic modelling approach.

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 an average rate of relative sea-level rise 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 quantification, understanding and prediction of the individual contributions to local relative sea level, with a focus on the most recent studies. Subsidence contributed to about half of the historical relative sea-level rise in Venice. The current best estimate of the average rate of sea-level rise during the observational period from 1872 to 2019 based on tide-gauge data after removal of subsidence effects is 1.23 ± 0.13 mm/year. A higher – but more uncertain – rate of sea-level rise is observed for more recent years. Between 1993 and 2019, an average change of about +2.76 ± 1.75 mm/year is estimated from tide-gauge data after removal of subsidence. Unfortunately, satellite altimetry does not provide reliable sea-level data within the Venice Lagoon. Local sea-level changes in Venice closely depend on sea-level variations in the Adriatic Sea, which in turn are linked to sea-level variations in the Mediterranean Sea. Water mass exchange through the Strait of Gibraltar and its drivers currently constitute a source of substantial uncertainty for estimating future deviations of the Mediterranean mean sea-level trend from the global-mean value. Regional atmospheric and oceanic processes will likely contribute significant interannual and interdecadal future variability in Venetian sea level with a magnitude comparable to that observed in the past. On the basis of regional projections of sea-level rise and an understanding of the local and regional processes affecting relative sea-level trends in Venice, the likely range of atmospherically corrected relative sea-level rise in Venice by 2100 ranges between 32 and 62 cm for the RCP2.6 scenario and between 58 and 110 cm for the RCP8.5 scenario, respectively. A plausible but unlikely high-end scenario linked to strong ice-sheet melting yields about 180 cm of relative sea-level rise in Venice by 2100. Projections of human-induced vertical land motions are currently not available, but historical evidence demonstrates that they have the potential to produce a significant contribution to the relative sea-level rise in Venice, exacerbating the hazard posed by climatically induced sea-level changes.

ILICO, a French Research Infrastructure (RI) for Coastal Ocean and Nearshore Observations is a notable example of national and pan-institutional efforts to expand knowledge of the complex processes at work within the critical coastal zone in line with the European Ocean Observing System perspective. Providing a forum for its community to work together on priority issues is a challenge, and ILICO’s organizational structure and governance are designed accordingly. Future challenges for this RI include the question of whether France’s original model of combining both land and nearshore in its study of the coastal domain is transferable to the pan-European context and how far we can go in integrating overseas and ultramarine issues.

In the context of global mean sea level rise, understanding the drivers of relative sea-level (RSL) at the coast is of major importance for coastal environments research and management. Since the 1990s, the combination of satellite altimetry observations with in situ tide gauge data has provided a better understanding of coastal sea level variability, but challenges remain to quantify the relative contributions of possible drivers (oceanic, vertical land motion (VLM), atmospheric and wave). Here, over the period 1993–2015, we combine concurrent observations from satellite altimetry, tide gauges, and oceanic model hindcast in order to identify the predominant drivers responsible for long-term variability of RSL at 434 coastal locations worldwide. We found that the dominant driver of the RSL trend is the ocean components in 76% of the cases, VLM in 17% and waves in 7%. Interestingly, no significant trend in the wave setup was noted over the period considered at most of our coastal stations. However, at some locations, we found significant correlations between the wave setup hindcasts and VLM data. Moreover, we evidence a substantial variance reduction in the VLM once corrected for the wave setup. We therefore recommend future studies aiming at VLM estimation to consider applying wave setup corrections to improve the comparability of the tide gauge and satellite altimetry measurements.

Part of the future harmonization work in the European network (assignment of unique identifiers or metadata management and standards) should rely in principle on the progress of the work at a global level, with the support of OceanOPS, as it is already done for other ocean observing systems.This report provides recommendations and action lines for the European network, including a proposal of station definition based on vertical land movement information, and a set of minimum mandatory metadata to be included for near-real time applications.In the framework of EuroSea WP3, the following on-going activities will be accomplished: i) completion of data portals gaps and duplicates analysis; ii) European tide gauge metadata inventory; iii) workshop focused on new automatic quality control algorithms and products from tide gauge data; and iv) new global sea level data portal based on Global Navigation Satellite System (GNSS) receivers installed to monitor land motion.