Measuring Sea Level with GPS-Equipped Buoys: A Multi-Instruments Experiment at Aix Island

Measuring sea-level in a global reference frame with sub-centimeter accuracy is a relevant challenge in the context of current global warming and associated sea-level rise. Global Navigation Satellite Systems (GNSS) can provide sea-level measurements directly referenced in an absolute geocentric frame. We present here the results of a multi-instruments experiment with three buoys equipped with Global Positioning System (GPS), a radar tide gauge and a tide pole. This experiment was carried out at Aix Island (West coast of France) on the 27-28 March 2012. The GPS buoys were evaluated against conventional tide gauge measurements through a Van de Casteele test. The Root Mean Square Error (RMSE) computed from the difference between the GPS-buoys and radar tide gauge data ranges from 1 cm to 2.2 cm, which is suitable for tidal applications and offers interesting perspectives for future sea-level variations studies.La medición del nivel del mar en un marco de referencias globales con una precisión subcentimétrica es un desafío importante en el contexto del calentamiento mundial actual y del aumento del nivel del mar asociado al mismo. Los Sistemas Mundiales de Navegación por Satélite (GNSS) pueden proporcionar medidas del nivel del mar directamente referenciadas en una estructura geocéntrica absoluta. Presentamos aquí los resultados de un experimento multi-instrumentos con tres boyas equipadas de un Sistema de Posiciona-miento Global (GPS), un mareógrafo con sistema de radar y una escala de mareas. Este experimento fue llevado a cabo en la Isla de Aix (Costa Occidental de Francia), los días 27 y 28 de Marzo del 2012. Las boyas GPS fueron evaluadas comparándolas con las medidas de los mareógrafos convencionales mediante un test Van de Casteele. El Error Cuadrático Medio (RMSE) calculado a partir de la diferencia entre los datos de las boyas GPS y los datos de mareógrafo, oscila de 1 a 2,2 cm, lo que es apropiado para las aplicaciones de mareas y ofrece perspectivas interesantes para futuros estudios de variaciones del nivel del mar.La mesure du niveau de la mer dans un référentiel mondial avec une précision sub-centimétrique est un défi pertinent dans le contexte actuel du réchauffement climatique et de l’élévation du niveau des mers qui en résulte. Les systèmes mondiaux de navigation par satellite (GNSS) peuvent fournir des mesures du niveau de la mer directement rapportées à un référentiel géocentrique absolu. Nous présentons ici les résultats d’une expérience multi-instruments avec trois bouées équipées d’un système de positionnement par satellite (GPS), un marégraphe à radar et une échelle de marée. Cette expérience a été effectuée à l’île d’Aix (côte ouest de la France) les 27 et 28 mars 2012. Les bouées GPS ont été éva-luées par rapport aux mesures du marégraphe conventionnel au moyen d’un test de Van de Casteele. L’erreur quadratique moyenne (RMSE) calculée à partir de la différence entre les données des bouées GPS et celles du marégraphe radar est comprise entre 1 cm et 2,2 cm, ce qui convient pour les applications marégraphique et offre d’intéressantes pers-pectives pour les futures études des variations du niveau de la mer

Estimation des biais et précisions des marégraphes par combinaison de plusieurs séries temporelles co-localisées.

International audienc

Trajectories of exposure and vulnerability of small islands to climate change

The authors thank the funding and logistical supports for the Back to the Future workshop (France, October 8–10, 2013) provided by the Corderie Royale de Rochefort, the Regional Council of Poitou-Charentes, the Conservatoire du Littoral, the Fondation de France, the Club Méditerranée, the Communautés d'agglomération de La Rochelle et du Pays Rochefortais, and the Université populaire du Littoral Charentais 17 and the French National Research Agency (CapAdapt project, ANR-2011-JSH1-004 01 and STORISK project, ANR-15-CE03-0003).This article advocates for a dynamic and comprehensive understanding of vulnerability to climate-related environmental changes in order to feed the design of adaptation future pathways. It uses the trajectory of exposure and vulnerability (TEV) approach that it defines as ‘storylines of driving factors and processes that have influenced past and present territorial system exposure and vulnerability to impacts associated with climate variability and change.’ The study is based on the analysis of six peer-reviewed Pacific island case studies covering various geographical settings (high islands vs low-lying reef islands, urban vs rural) and hazards associated with climate variability and change; that addressed the interactions between natural and anthropogenic driving factors; and adopted multidecadal past-to-present approaches. The findings emphasize that most urban and rural reef and high islands have undergone increasing exposure and vulnerability as a result of major changes in settlement and demographic patterns, lifestyles and economies, natural resources availability, and environmental conditions. The article highlights three generic and successive periods of change in the studied islands’ TEV: from geopolitical and political over the colonization-to-political independence period; to demographic, socio-economic, and cultural from the 1960s to the 1980s; culminating in the dominance of demographic, socio-economic, cultural, and environmental drivers since the 1980s. Based on these empirical insights, the article emphasizes the existence of anthropogenic-driven path-dependency effects in TEV, thus arguing for the analysis of the temporal dimensions of exposure and vulnerability to be a prerequisite for science to be able to inform policy- and decision-making processes toward robust adaptation pathways.PostprintPeer reviewe

Conception d'un système modulaire de collecte de données embarqué sur le drone marin PAMELI

International audienceThe PAMELI project (Multidimensional Autonomous Platform for Interdisciplinary Littoral Exploration) focuses on the repeated observation of environmental parameters such as physico-chemical parameters of the water column (Ph, salinity, conductivity), water depth and precise altimetry using a marine drone. This project first developed in Pertuis Charentais, since July 2018. One of the challenges of this project is to design an information system for data collection that is robust, reliable and flexible, ie to guarantee the good conditions for archiving and replaying data according to FAIR principles (Findable, Accessible, Interoperable and Reusable).This poster details the solutions put in place in an embedded information system to ensure this level of data quality requirements, and to meet the constraints of this embedded system (low energy resources, no Internet access, sensors removable, scalable and heterogeneous in their mode of communication). In particular, it shows how the operators of the drone can visualize the collected data in real time to intervene quickly in case of failure, or record annotations during the mission of the drone that will adjust the data qualification methods.Le projet PAMELI (Plateforme Autonome Multicapteurs pour l'Exploration Littorale Interdisciplinaire) porte sur l'observation répétée des paramètres environnementaux tels que les paramètres physico-chimiques de la colonne d'eau (Ph, salinité, conductivité), la profondeur d'eau et l'altimétrie précise à l'aide d'un drone marin. Ce projet se développe dans un premier temps dans les Pertuis Charentais, depuis juillet 2018. Un des enjeux de ce projet est de concevoir un système d'information pour la collecte des données qui soit robuste, fiable et flexible, i.e. permettant de garantir les bonnes conditions d'archivage et de rediffusion des données suivant les principes du FAIR (Findable, Accessible, Interoperable and Reusable). Ce poster détaille donc les solutions mises en place dans un système d’information embarqué pour assurer ce niveau d’exigences concernant la qualité des données, et de répondre aux contraintes de ce système embarqué (faibles ressources énergétiques, pas d’accès Internet, capteurs amovibles, évolutifs et hétérogènes dans leur mode de communication). En particulier, il montre comment les opérateurs du drone peuvent visualiser les données collectées en temps réel pour intervenir rapidement en cas de panne, ou enregistrer des annotations durant la mission du drone qui permettront d’ajuster les méthodes de qualification des données

Crustal structure of the Mid-Atlantic Ridge south of the Kane Fracture Zone from seafloor and sea surface gravity data

International audienceSeafloor and sea surface gravity data are inverted together to construct a model for the near-axis crustal structure of a slow spreading ridge. The seafloor data set offers two main advantages: it allows us to recover shorter-wavelengths signal and to constrain the value of a potential field at two different levels. The model we propose here would not have been derived from sea surface data alone. It is based on a dense sea surface gravity coverage and on 121 sea bottom gravity measurements collected in the Mid-Atlantic Ridge at Kane (MARK) area, during the Hydrosnake (1988) and Gravinaute (1993) cruises. The primary goal of the seafloor surveys was to test for the presence of a magma reservoir beneath the axial neovolcanic ridge. First, a forward two-dimensional (2-D) model of the crustal structure across the axis is fit to observed gravity anomalies, using constraints from geological and structural observations. Bouguer anomalies computed from sea bottom measurements and downward continuation of sea surface measurements both constrain the forward modeling. This forward model is the starting point of a 2-D Monte Carlo inversion of seafloor and sea surface data. In addition to the crustal thickness variations along-axis, our data document the amplitude variations of the crustal thickness and/or its density in the across-axis direction. The model resulting from our inversion exhibits several features of the crustal structure in the MARK area: (1) The presence of a low-density (Ap =-300_+ 50 kg/m 3) body beneath the neovolcanic ridge is suggested and could correspond to a magma chamber, or more probably to a highly hydrothermally fissured zone. (2) Both long-and short-wavelength gravity signals exhibit a difference between the western and eastern sides of the axial domain: the mean value and the amplitude of Bouguer anomalies are higher on the western part. This difference suggests that axial processes, in this area, are very asymmetric. (3) Abyssal hills are not associated with a single gravity signature: for instance, on the west side of the axis, one of the explored hills has no Bouguer anomaly and is interpreted as a neovolcanic ridge, whereas the others are associated with a shifted Bouguer anomaly high and are interpreted as having thinner magmatic crust. (4) The last feature of the crustal fabric we document here is the asymmetric emplacement of some deep rocks outcrops. In the MARK area, we find that "Pink Hill," a topographic high where serpentinized peridotites are outcropping, is much more serpentinized on its east flank, toward the axial valley, than on its west flank. Alteration occurring mainly by fluid circulation through faulted zones, the asymmetric serpentinization suggests that deep-origin rocks have outcropped by means of a main fault zone and are not emplaced by diapirism

Towards comprehensive observing and modeling systems for monitoring and predicting regional to coastal sea level

A major challenge for managing impacts and implementing effective mitigation measures and adaptation strategies for coastal zones affected by future sea level (SL) rise is our limited capacity to predict SL change at the coast on relevant spatial and temporal scales. Predicting coastal SL requires the ability to monitor and simulate a multitude of physical processes affecting SL, from local effects of wind waves and river runoff to remote influences of the large-scale ocean circulation on the coast. Here we assess our current understanding of the causes of coastal SL variability on monthly to multi-decadal timescales, including geodetic, oceanographic and atmospheric aspects of the problem, and review available observing systems informing on coastal SL. We also review the ability of existing models and data assimilation systems to estimate coastal SL variations and of atmosphere-ocean global coupled models and related regional downscaling efforts to project future SL changes. We discuss (1) observational gaps and uncertainties, and priorities for the development of an optimal and integrated coastal SL observing system, (2) strategies for advancing model capabilities in forecasting short-term processes and projecting long-term changes affecting coastal SL, and (3) possible future developments of sea level services enabling better connection of scientists and user communities and facilitating assessment and decision making for adaptation to future coastal SL change.RP was funded by NASA grant NNH16CT00C. CD was supported by the Australian Research Council (FT130101532 and DP 160103130), the Scientific Committee on Oceanic Research (SCOR) Working Group 148, funded by national SCOR committees and a grant to SCOR from the U.S. National Science Foundation (Grant OCE-1546580), and the Intergovernmental Oceanographic Commission of UNESCO/International Oceanographic Data and Information Exchange (IOC/IODE) IQuOD Steering Group. SJ was supported by the Natural Environmental Research Council under Grant Agreement No. NE/P01517/1 and by the EPSRC NEWTON Fund Sustainable Deltas Programme, Grant Number EP/R024537/1. RvdW received funding from NWO, Grant 866.13.001. WH was supported by NASA (NNX17AI63G and NNX17AH25G). CL was supported by NASA Grant NNH16CT01C. This work is a contribution to the PIRATE project funded by CNES (to TP). PT was supported by the NOAA Research Global Ocean Monitoring and Observing Program through its sponsorship of UHSLC (NA16NMF4320058). JS was supported by EU contract 730030 (call H2020-EO-2016, “CEASELESS”). JW was supported by EU Horizon 2020 Grant 633211, Atlantos

Ground deformation monitoring of the eruption offshore Mayotte

In May 2018, the Mayotte island, located in the Indian Ocean, was affected by an unprecedented seismic crisis, followed by anomalous on-land surface displacements in July 2018. Cumulatively from July 1, 2018 to December 31, 2021, the horizontal displacements were approximately 21 to 25 cm eastward, and subsidence was approximately 10 to 19 cm. The study of data recorded by the on-land GNSS network, and their modeling coupled with data from ocean bottom pressure gauges, allowed us to propose a magmatic origin of the seismic crisis with the deflation of a deep source east of Mayotte, that was confirmed in May 2019 by the discovery of a submarine eruption, 50 km offshore of Mayotte ([Feuillet et al., 2021]). Despite a non-optimal network geometry and receivers located far from the source, the GNSS data allowed following the deep dynamics of magma transfer, via the volume flow monitoring, throughout the eruption