Altimetry for the future: Building on 25 years of progress

In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the ‘‘Green” Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instruments’ development and satellite missions’ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion

Altimetry for the future: building on 25 years of progress

In 2018 we celebrated 25 years of development of radar altimetry, and the progress achieved by this methodology in the fields of global and coastal oceanography, hydrology, geodesy and cryospheric sciences. Many symbolic major events have celebrated these developments, e.g., in Venice, Italy, the 15th (2006) and 20th (2012) years of progress and more recently, in 2018, in Ponta Delgada, Portugal, 25 Years of Progress in Radar Altimetry. On this latter occasion it was decided to collect contributions of scientists, engineers and managers involved in the worldwide altimetry community to depict the state of altimetry and propose recommendations for the altimetry of the future. This paper summarizes contributions and recommendations that were collected and provides guidance for future mission design, research activities, and sustainable operational radar altimetry data exploitation. Recommendations provided are fundamental for optimizing further scientific and operational advances of oceanographic observations by altimetry, including requirements for spatial and temporal resolution of altimetric measurements, their accuracy and continuity. There are also new challenges and new openings mentioned in the paper that are particularly crucial for observations at higher latitudes, for coastal oceanography, for cryospheric studies and for hydrology. The paper starts with a general introduction followed by a section on Earth System Science including Ocean Dynamics, Sea Level, the Coastal Ocean, Hydrology, the Cryosphere and Polar Oceans and the “Green” Ocean, extending the frontier from biogeochemistry to marine ecology. Applications are described in a subsequent section, which covers Operational Oceanography, Weather, Hurricane Wave and Wind Forecasting, Climate projection. Instruments’ development and satellite missions’ evolutions are described in a fourth section. A fifth section covers the key observations that altimeters provide and their potential complements, from other Earth observation measurements to in situ data. Section 6 identifies the data and methods and provides some accuracy and resolution requirements for the wet tropospheric correction, the orbit and other geodetic requirements, the Mean Sea Surface, Geoid and Mean Dynamic Topography, Calibration and Validation, data accuracy, data access and handling (including the DUACS system). Section 7 brings a transversal view on scales, integration, artificial intelligence, and capacity building (education and training). Section 8 reviews the programmatic issues followed by a conclusion

Lagrangian analysis of satellite-derived currents: Application to the North Western Mediterranean coastal dynamics

Optimal interpolation methods for improving the reconstruction of coastal dynamics from along-track satellite altimetry measurements have been recently developed over the North Western Mediterranean Sea. Maps of satellite-derived geostrophic current anomalies are generated using these methods, and added to different mean circulation fields in order to obtained absolute geostrophic currents. The resulting fields are then compared to standard AVISO products, and their accuracies are assessed with Lagrangian diagnostics. The trajectories of virtual particle clusters are simulated with a Lagrangian code either with new current fields or with the AVISO ones. The simulated trajectories are then compared to 16 in situ drifter trajectories to evaluate the performance of the different velocity fields. The comparisons show that the new current fields lead to better results than the AVISO one, especially over the shallow continental shelf of the Gulf of Lion. However, despite the use of innovative strategies, some altimetry limitations still persist in the coastal domain, where small scale processes remain sub-sampled by conventional altimetry coverage but will benefit from technological development in the near future. Some of the limitations of the Lagrangian diagnostics presently used are also analyzed, but dedicated studies will be required for future further investigations. © 2014 COSPAR. Published by Elsevier Ltd. All rights reserved.The LATEX project is supported by the programs LEFE/IDAO and LEFE/CYBER of the INSU-Institut National des Sciences de l’Univers and by the Region PACA-Provence Alpes Côte dAzur. The altimeter (M)SLA were produced by SSALTO/DUACS and distributed by AVISO with support from CNES-Centre National d’Etude Spatiale. We particularly thank Milena Menna (OGS, Trieste, Italy) for processing and providing edited drifter data used within this study. Francesco Nencioli acknowledges support from the FP7 Marie Curie Actions of the European Commission, via the Intra-European Fellowship (FP7-PEOPLE-IEF-2011), project “Lyapunov Analysis in the COaSTal Environment” (LACOSTE-299834). Jérôme Bouffard is financed by a CNES post-doctoral grant.Peer Reviewe

A multi-platform approach to investigate submesoscale structures in a coastal region and their impacts in regulating cross-shelf exchanges

The interactions between ageostrophic processes and large scale dynamics in the western part of the Gulf of Lion (NW Mediterranean) play a fundamental role in regulating water exchanges between the continental shelf and the open sea. The dominant regimes emerging from these interactions were successfully characterized during the Lagrangian Transport Experiment (LATEX, 2008-2010) thanks to a multi-platform approach which included in-situ observations, satellite measurements and numerical model simulations. During the Latex10 campaign (September 1-24, 2010), in-situ Lagrangian Coherent Structures reconstructed from drifter trajectories allowed to identify an alongshore corridor through which coastal waters escaped the Gulf. Satellite imagery indicated that the offshore boundary of the corridor was associated with a strong frontal region. Glider profiles allowed to reconstruct the vertical structure of the front, and ship-based ADCP currents to estimate the associated horizontal fluxes. Realistic numerical simulations showed that this regime alternates with periods during which the circulation is dominated by coastal anticyclones (also observed in previous campaigns). Model results, along with a regional satellite altimetry product, allowed to characterize the influence of the two regimes in regulating cross-shelf exchanges

Variability of slope current positioning from space: Application to the Northern Current in the North Western Mediterranean Sea

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Process studies at the air-sea interface after atmospheric deposition in the Mediterranean Sea: objectives and strategy of the PEACETIME oceanographic campaign (May–June 2017)

In spring, the Mediterranean Sea, a well-stratified low nutrient low chlorophyll region, receives atmospheric deposition both desert dust from the Sahara and airborne particles from anthropogenic sources. Such deposition translates into a supply of new nutrients and trace metals for the surface waters that likely impact biogeochemical cycles. However, the quantification of the impacts and the processes involved are still far from being assessed in situ. In this paper, we provide a state of the art regarding dust deposition and its impact on the Mediterranean Sea biogeochemistry and we describe in this context the objectives and strategy of the PEACETIME project and cruise, entirely dedicated to filling this knowledge gap. Our strategy to go a step forward than in previous approaches in understanding these impacts by catching a real deposition event at sea is detailed. The PEACETIME oceanographic campaign took place in May–June 2017 and we describe how we were able to successfully adapt the planned transect in order to sample a Saharan dust deposition event, thanks to a dedicated strategy, so-called Fast Action. That was successful, providing, for the first time in our knowledge, a coupled atmospheric and oceanographic sampling before, during and after an atmospheric deposition event. Atmospheric and marine in situ observations and process studies have been conducted in contrasted area and we summarize the work performed at sea, the type of data acquired and their valorization in the papers published in the special issue

Introduction: Process studies at the air–sea interface after atmospheric deposition in the Mediterranean Sea – objectives and strategy of the PEACETIME oceanographic campaign (May–June 2017)

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New insights of the Sicily Channel and southern Tyrrhenian Sea variability

International audienceThe dynamics of the Sicily Channel and the southern Tyrrhenian Sea are highly influenced by the seasonal variability of the Mediterranean basin-wide circulation, by the interannual variability of the numerous mesoscale structures present in the Channel, and by the decadal variability of the adjacent Ionian Sea. In the present study, all these aspects are investigated using in-situ (Lagrangian drifter trajectories and Argo float profiles) and satellite data (Absolute Dynamic Topography, Sea Level Anomaly, Sea Surface Temperature, wind products) over the period from 1993 to 2018. The availability of long time series of data and high-resolution multi-sensor surface currents allow us to add new details on the circulation features and on their driving mechanisms and to detect new permanent eddies not yet described in literature. The structures prevailing in winter are mainly driven by wind, whereas those prevailing in summer are regulated by topographical forcing on surface currents. The strength of the surface structures located at the western entrance of the Ionian Sea and of the mesoscale activity along the northern Sicily coast is modulated by the large-scale internal variability. The vertical hydrological characteristics of these mesoscale eddies are delineated using the Argo float profiles inside these structure

PROTEVS-MED field experiments: very high resolution hydrographic surveys in the Western Mediterranean Sea

From 2015 to 2018 four field experiments (seven legs) were performed in the Western Mediterranean basin during winter or early spring. The main objectives were the assessment of high-resolution modeling and the observation of mesoscale structure and associated ageostrophic dynamics. Thanks to the intensive use of a towed vehicle undulating in the upper oceanic layer between 0 and 400 m depth (SeaSoar), a large number of very high resolution hydrographic transects (total length about 10 000 km) were measured, observing mesoscale dynamics (slope current and its instabilities, anticyclonic eddies, submesoscale coherent vortices, frontal dynamics, convection events, strait outflows) and submesoscale processes like stirring, mixed-layer or symmetric instabilities. When available, the data were completed with velocities recorded by a vessel-mounted acoustic Doppler current profiler (VMADCP) and by surface salinity and temperature recorded by a thermosalinograph (TSG). Classical full-depth CTD (conductivity, temperature, depth) stations were also used, providing the background hydrography of the deeper layers when focusing on peculiar structures. In 2017, a free-fall profiler (MVP-200; MVP – moving vessel profiler) was deployed to manage even higher horizontal resolutions. In 2018, another free-fall profiler (a rapidCAST) was tested. When available, biological sensors (chlorophyll a, turbidity, dissolved oxygen, etc.) were used. They provided useful complementary observations about the circulation. This dataset is an unprecedented opportunity to investigate the very fine scale processes, as the Mediterranean Sea is known for its intense and contrasting dynamics. It should be useful for modellers (who reduce the grid size below a few hundred meters) and should properly resolve finer-scale dynamics. Likewise, theoretical work could also be illustrated by in situ evidence embedded in this dataset. The data are available through the SEANOE repository at: https://doi.org/10.17882/62352 (Dumas et al., 2018