[1] Dynamics along the continental slopes are difficult to observe given the wide spectrum of temporal and spatial variability of physical processes which occur (coastal currents, meanders, eddies, etc.). Studying such complex dynamics requires the development of synergic approaches that use integrated observing systems. In this context, we present the results of an observational program conducted in the Balearic Sea combining coastal gliders and altimetry. The objectives of this experiment are to study regional dynamics using new technologies, such as gliders, in synergy with satellite altimetry and to investigate the limitations and potential improvement to altimetric data sets in the coastal zone. In this regard, new methodologies have been developed to compute consistent altimetric and glider velocities, and a novel technique to estimate absolute glider velocities, combining surface glider geostrophic velocities with integrated currents estimated from the glider GPS positioning, has been applied. In addition, the altimetric velocity computation has been improved, especially in the coastal zone, using high-frequency along-track sampling associated with new filtering and editing techniques. This approach proves efficient for homogenizing the physical contents of altimetry and glider surface currents (percentage of standard deviation explained is >40) and characterizing regional dynamics in the Balearic Sea through a combined analysis of a high-resolution observing system, such as the appearance of anomalous intense mesoscale features missing in the classical circulation scheme of the Balearic Sea.Citation: Bouffard, J., A. Pascual, S. Ruiz, Y. Faugère, and J. Tintoré (2010), Coastal and mesoscale dynamics characterization using altimetry and gliders: A case study in the

Coastal zones are highly dynamical systems affected by a variety of natural and anthropogenic forcing factors that include sea level rise, extreme events, local oceanic and atmospheric processes, ground subsidence, etc. However, so far, they remain poorly monitored on a global scale. To better understand changes affecting world coastal zones and to provide crucial information to decision-makers involved in adaptation to and mitigation of environmental risks, coastal observations of various types need to be collected and analyzed. In this white paper, we first discuss the main forcing agents acting on coastal regions (e.g., sea level, winds, waves and currents, river runoff, sediment supply and transport, vertical land motions, land use) and the induced coastal response (e.g., shoreline position, estuaries morphology, land topography at Frontiers in Marine Science | www.frontiersin.org 1 July 2019 | Volume 6 | Article 348Benveniste et al.Requirements for a Coastal Zone Observing System the land-sea interface and coastal bathymetry). We identify a number of space-based observational needs that have to be addressed in the near future to understand coastal zone evolution. Among these, improved monitoring of coastal sea level by satellite altimetry techniques is recognized as high priority. Classical altimeter data in the coastal zone are adversely affected by land contamination with degraded range and geophysical corrections. However, recent progress in coastal altimetry data processing and multisensor data synergy, offers new perspective to measure sea level change very close to the coast. This issue is discussed in much detail in this paper, including the development of a global coastal sea-level and sea state climate record with mission consistent coastal processing and products dedicated to coastal regimes. Finally, we present a new promising technology based on the use of Signals of Opportunity (SoOp), i.e., communication satellite transmissions that are reutilized as illumination sources in a bistatic radar configuration, for measuring coastal sea level. Since SoOp technology requires only receiver technology to be placed in orbit, small satellite platforms could be used, enabling a constellation to achieve high spatio-temporal resolutions of sea level in coastal zones.

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[1] We present an innovative approach to the generation of remotely sensed high-resolution sea surface topography that improves coastal and mesoscale dynamic characterization. This new method is applied for the period 2002-2010 in the northwestern Mediterranean Sea, an area marked by a small Rossby radius. The spectral content of the new mapped data is closer to that of the along-track signal and displays higher levels of energy in the mesoscale bandwidth with the probability distribution of the new velocity fields 30% closer to drifter estimations. The fields yield levels of eddy kinetic energy 25% higher than standard altimetry products, especially over regions regularly impacted by mesoscale instabilities. Moreover, qualitative and quantitative comparisons with drifters, glider, and satellite sea surface temperature observations further confirm that the new altimetry product provides, in many cases, a better representation of mesoscale features (more than 25% improvement in correlation with glider data during an experiment). Citation: Escudier, R., J. Bouffard, A. Pascual, P.-M. Poulain, and M.-I. Pujol (2013), Improvement of coastal and mesoscale observation from space: Application to the northwestern Mediterranean Sea, Geophys.