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Thanks to its current accuracy and maturity, altimetry is considered as a fully operational observing system dedicated to various applications such as climate studies. Altimeter measurements are corrected from several geophysical parameters in order to isolate the oceanic variability and tide correction is one of the most critical. The accuracy of tidal models has been much improved for the last 25 years leading to centimetric accuracy in the open ocean. The last release of the global tidal model, referenced as FES2014b was distributed in mid-2016.The underlying unstructured mesh resolution of FES2014b was increased in areas of interest like shallow waters and on the slope of the continental shelves, and the error of the pure hydrodynamic ocean solution has been divided by a factor of 2 compared to the previous version (FES2004). Still, some significant errors remain in some regions, due to the omission of compound tides and bathymetric errors (in shelf/coastal seas), seasonal sea ice effects, and lack of available data for assimilation (in the high latitudes).To address the reduction of these errors and face the new challenges of the tide correction for HR altimetry, in particular, the forthcoming SWOT mission, a new global tide model FES2022 has been developed, focusing particularly on shallow waters and high latitudes.This new tidal solution uses higher spatial resolution in coastal areas, extending systematically the model mesh to the narrowest coastal systems (fjords, estuaries, …), and the model bathymetry has been upgraded in many places thanks to an international collaboration effort. The hydrodynamic modeling benefits also from further improvements which allow producing very accurate hydrodynamic simulations. The use of the most recent altimeter standards and high inclination altimeters like Cryosat-2, Saral/AltiKa, and even Sentinel-3, also allowed retrieving some tide observations in the highest latitudes to help improving the polar tides modeling. Results show a great improvement in the FES2022 hydrodynamic solution compared to FES2014’s one. The assimilation procedure was conducted, and a specific loading tide solution was produced. The final FES2022 tidal solution was validated in comparison to the FES2014b, EOT20, GOT, and TPXO9v5 models, for the missions Jason 3, Sentinel-3A, and Cryosat-2. Some validations of the new FES2022 tidal current are also presented here.

A new Mean Sea Surface model, the CNES_CLS_2021 MSS, has been determined. It is based on the integration of more than 27 years of altimetric data, using more than 10 altimeters from the historical Topex/Poseidon to the in-flight Sentienl-3A/B missions, including ERM and geodetic/drifting orbits. As the previous 2015 version this new MSS is focused on the fallowing points of improvement which remains a permanent challenge: • the correction of ocean variability, especially for wavelengths lover than 200 km. • the accuracy of altimetric data and therefore of the MSS near the coast. • a most accurate mapping of the finest topographic structures until wavelengths shorter than 10 km. A particular attention was also paid to the Arctic area by combining traditional SSH with leads. We therefore propose a synthesis of analyzes of these different aspects in order to quantify the improvements of this new MSS compared to other existing MSS.

The Hunga-Tonga submarine volcano produced a violent explosion on Saturday 15/01/2022 at approximately 04:15 UT (17:15 local time). The explosion generated a tsunami affecting all the Pacific Ocean. The tsunami has been detected in the multimission (Duacs) operational Sea Level products ingesting the flying altimeters Jason-3, Sentinel-3A, Sentinel-3B provided by Eumetsat, Cryosat-2, Saral, HY-2B provided by Cnes. After a specific processing carried out to remove the natural variability of the ocean, the tsunami signal was detected very clearly in the constellation, notably on HY2B, first to fly over the area 1h30 after the eruption. Comparisons to models show a position mismatch in the NRT predictions, demonstrating the interest of altimetry in tsunami analyses. The signature of the tsunami was also detected in radar images from the Copernicus Sentinel-1A synthetic aperture radar (SAR) satellite. the peak wavelength of the retrieved waves was estimated allowing us to track them back near the center of the eruption, therefore confirming that they were generated by this event. This paper describes the tsunami signal as observed by the altimetry constellation and Sentinel1A.

Although CFOSAT is dedicated to wind and wave characterization the Ku altimeter on board has the capacity of providing and Sea level measurements, relevant to enrich the DUACS (Data Unification and Altimeter Combination System) Sea Level Anomaly products for the benefit of the Copernicus Marine Service users. With an orbit reaching 82° latitude, it could in particular help to compensate the loss of current nadir missions at low and high latitudes. The short and long wavelength errors of CFOSAT Sea Level Anomaly were investigated and specific procedures, based on a multimission approach, were implemented in order to correct from the poor orbit accuracy. Once homogenized to the other missions, the CFOSAT provide an interesting set of Sea Level, with a good quality at mesoscale. Across track geostrophic current were derived providing an unprecedented global colocation of wave spectra and currents. Based on these studies, a Level3 demonstration product were produced and will be available on Aviso.

Sea Surface Height (SSH) information is available all over the world thanks to satellite altimetry measurements. Data processing and mapping algorithms produce sea level products that are part of ocean monitoring variables. In order to provide this information to marine environment actors, Copernicus Marine Service Program (CMEMS) created an operational ocean mapping algorithm called Data Unification and Altimeter Combination System (DUACS). This processing system uses data provided by currently flying altimeters (Sentinel, Jason, SaRal...) and supplies two types of SSH products : L3 (along-track) and L4 (gridded map). Next generation altimeter satellite SWOT will be launched late 2022 and will embark a new sensor based on Ka band. It will display high resolution SSH measurements on both side of its track across two swaths of 50 km. This is a major breakthrough because existing altimeters can only measure SSH along their tracks by pointing at nadir. All scientists and engineers of DUACS are hoping for new mission SWOT to improve the quality of L3 and L4 products. In that sense, this study focuses on the improvement in resolution of L4 gridded products thanks to SWOT satellite. In order to answer that question, 3 OSSEs were carried out in order to evaluate the performances of 3 different kinds of SSH observation systems : a) 3 Nadirs, b) 1 SWOT and c) 3 Nadirs + 1 SWOT. By comparing OSSEs one another it will be possible to assess both the performances of SWOT compared to 3 nadirs satellites and the benefit when SWOT is added to a 3 nadirs constellation. Results show that SWOT has a higher spatial resolution than 3 Nadirs at high latitudes, which is due to its high spatial sampling. At mid latitudes, SWOT enables to detect smaller structures only in low variability zones. Within energetic western boundary currents such as Gulf Stream or Kuroshio, 3 Nadirs constellation has a better temporal sampling and provides higher spatial and temporal resolution. In order to confirm these diagnosis, eddy detection algorithms were launched on SSH recontructed maps. Results show that detected eddies density is correlated with higher spatial resolution zones. The OSSE computing 3 Nadirs + SWOT data shows that the benefit of SWOT is unequal over the globe. It improves the spatial resolution everywhere, with limited effect in Western boundary currents and along the Equator. Yet, temporal resolution can get worse when SWOT is added, especially in zones where barotropic current is poorly evaluated.

For more than 23 years, the multisatellite DUACS system has been providing high quality multi-mission altimetry Sea Level products for oceanographic applications, climate forecasting centers, geophysics and biology communities. They consist in directly usable and easy to manipulate Level 3 (along-track cross-calibrated Sea Level Anomaly SLA) and Level 4 (multiple sensors merged gridded gap-free) products. Global and regional datasets (Arctic Ocean, European Seas ...) are available. A full reprocessing of these products is carried out almost every 3 years, based on the state-of-the-art Level 2 to Level 4 algorithms. In Decembre 2021, a new version will be available within the Copernicus Marine Environment and Monitoring Service (CMEMS) and the Copernicus Climate Change Service (C3S) covering 28 years of altimetric data (i.e. almost a century of cumulated data using 24 altimetric missions). This version benefits from major improvements associated with new altimeter and mapping standards. Here, we report the first results of this DUACS DT2021 multi-mission reprocessing. We first describe the main steps of the altimeter production system. Then, we discuss the characteristics and limits of the different products (C3S, CMEMS) in order to help the ocean and climate communities on their optimal use for validation, assimilation activities and other scientific studies. Several comparisons with independent datasets (along-track, drifters, tide gauges) show that a significant improvement has been achieved at mesoscale with this new version: almost 20% of SLA error reduction at wavelengths [65, 500km] and around 10% of geostrophic currents error reduction compared to the previous version (DT2018). At decadal time scale, the trend of the global mean sea level has been estimated to 3.4 +/- 0.4 mm/yr. (90% Confidence Interval), in line with other estimates and previous reprocessing DUACS-DT2018. New altimeter corrections are also available for the users (internal waves, correction for the Topex-A instrumental drift, flag ice).

Thanks to its current accuracy and maturity, altimetry is considered as a fully operational observing system dedicated to various applications such as climate studies. Altimeter measurements are corrected from several geophysical parameters in order to isolate the oceanic variability and the tide correction is one of the most critical. The accuracy of tidal models has been much improved for last 25 years leading to centimetric accuracy in the open ocean. The last release of the global tidal model, referenced as FES2014b was distributed since mid-2016. The underlying unstructured mesh resolution of FES2014b was increased in areas of interest like shallow waters and on the slope of the continental shelves, and the error of the pure hydrodynamic ocean solution has been divided by a factor of 2 compared to previous version (FES2004). Still, some significant errors remain in some regions, due to the omission of compound tides and bathymetric errors (in shelf/coastal seas), seasonal sea ice effects and lack of available data for assimilation (in the high latitudes). To address the reduction of these errors and facing the new challenges of the tide correction for HR altimetry, in particular the forthcoming SWOT mission, a new global tide model FES2022 has been developed, focusing particularly on shallow waters and high latitudes. This new tidal solution uses higher spatial resolution in coastal areas, extending systematically the model mesh to the narrowest coastal systems (fjords, estuaries, …), and the model bathymetry has been upgraded in many places thanks to an international collaboration effort. The hydrodynamic modelling benefits also from further improvements which allows producing very accurate hydrodynamic simulations. The use of the most recent altimeter standards and high inclination altimeters like Cryosat-2, Saral/AltiKa and even Sentinel-3, also allowed retrieving some tide observations in the highest latitudes to help improving the polar tides modelling. Preliminary results show a great improvement of the FES2022 hydrodynamic solution compared to FES2014’s one. The assimilation procedure is on-going and a specific loading tide solution will also be produced in the coming months. Some validation results of the new FES2022 global tidal solution are presented here.

The Copernicus Marine Environment Monitoring Service (CMEMS) provides regular and systematic reference information on the physical and biogeochemical ocean and sea-ice state for the global ocean and the European regional seas. CMEMS serves a wide range of users (more than 15,000 users are now registered to the service) and applications. Observations are a fundamental pillar of the CMEMS value-added chain that goes from observation to information and users. Observations are used by CMEMS Thematic Assembly Centres (TACs) to derive high-level data products and by CMEMS Monitoring and Forecasting Centres (MFCs) to validate and constrain their global and regional ocean analysis and forecasting systems. This paper presents an overview of CMEMS, its evolution, and how the value of in situ and satellite observations is increased through the generation of high-level products ready to be used by downstream applications and services. The complementary nature of satellite and in situ observations is highlighted. Long-term perspectives for the development of CMEMS are described and implications for the evolution of the in situ and satellite observing systems are outlined. Results from Observing System Evaluations (OSEs) and Observing System Simulation Experiments (OSSEs) illustrate the high dependencies of CMEMS systems on observations. Finally future CMEMS requirements for both satellite and in situ observations are detailed.