Funcionamiento de mareógrafos modernos: hacia la precisión milimétrica

Considerable efforts are being made worldwide to upgrade tide gauge networks using new technologies. Because of the unique location of the Kerguelen Islands, the measurement of sea level there has received particular attention, with up to four systems equipped with modern sensors functioning simultaneously (two pressure tide gauges, a radar tide gauge, and a GPS-equipped buoy). We analysed and compared the sea level data obtained with these systems from 2003 to 2010, together with a time series of tide pole observations. This is the first time that a multi-comparison study with tide gauges has been undertaken over such a long time span and that the stability of modern radar tide gauges has been examined. The multi-comparison enabled us to evaluate the performance of the tide gauges in several frequency ranges, identify errors and estimate their magnitude. The drift of the pressure sensors (up to 8.0 mm/yr) was found to be one of the most relevant sources of systematic error. Other sources of difference such as clock drift, scale error and different locations of the instruments were also detected. After correcting the time series of sea level for these errors we estimated an upper bound for the radar instrumental error in field condition at ~0.3 cm.Actualmente se están realizando muchos esfuerzos para renovar las redes maregráficas utilizando nuevas tecnologías. En este contexto, la monitorización del nivel del mar en las islas Kerguelen ha recibido una atención particular debido a su localización única. Hasta cuatro equipos han realizado medidas simultáneamente: dos mareógrafos de presión, un mareógrafo radar y una boya GPS. En este trabajo se analizan y comparan los datos obtenidos con dichos equipos desde 2003 hasta 2010, complementándolos con observaciones realizadas con una escala de marea. Es la primera vez que se plantea una comparación de estas características durante un periodo de tiempo tan largo, y que se aborda el estudio de la estabilidad de los mareógrafos radar a largo plazo. La comparación permitió evaluar el comportamiento de los mareógrafos en distintos rangos de frecuencia, identificar errores y estimar su magnitud. La deriva del sensor de presión apareció como la fuente de error más relevante (hasta 8 mm/año). También se detectaron otras fuentes de diferencias como derivas en el reloj, el error de escala o la diferente localización de los instrumentos. Tras corregir esos errores fue posible estimar un límite superior de ~0.3 cm para el error instrumental del radar en condiciones de campo

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

Extension of high temporal resolution sea level time series at Socoa (Saint Jean-de-Luz, France) back to 1875

In this data paper sea level time series at Socoa (Saint Jean-de-Luz, Southwestern France) is extended in a data archaeology exercise. We have catalogued water level records stored in ledgers and charts, as well as other associated documents (metadata) in thorough research of national and local archives. An extensive effort was made to rescue these documents by archiving them in digital formats. Based on this large set of rescued documents, the Socoa time series is further extended back in time by about 40 years, at hourly (for ledgers) to 5-minutes (for charts) sampling. Analysis of the precise levelling information reveals that the datum of the tide gauge site has been stable. We assessed the consistency of this new century-long time series based on nearby tide gauge data. Although the overall timeseries is generally consistent, siltation is found to be a recurrent problem of the stilling well which impacted some part of the extended data. However, being a high temporal resolution sea level time series spanning more than 100 years, this new dataset will be useful for advancing climate research, particularly the decadal scale variations in the North Atlantic, as well as the storminess and extreme events along the French Basque coastal region.</p

Tide gauges

Tide gauge measurements provide data for routine tidal predictions in ports as well as for extreme events such as storm surges and tsunamis. Along with satellite altimeter measurements, tide gauges also provide measurements used for sea-level rise estimates. This is particularly important for impact assessment in low-lying coastlines of south Asia as well as islands such as the Maldives in the Indian Ocea

Increased population exposure to Amphan‐scale cyclones under future climates

International audienceAbstract Southern Asia experiences some of the most damaging climate events in the world, with loss of life from some cyclones in the hundreds of thousands. Despite this, research on climate extremes in the region is substantially lacking compared to other parts of the world. To understand the narrative of how an extreme event in the region may change in the future, we consider Super Cyclone Amphan, which made landfall in May 2020, bringing storm surges of 2–4 m to coastlines of India and Bangladesh. Using the latest CMIP6 climate model projections, coupled with storm surge, hydrological, and socio‐economic models, we consider how the population exposure to a storm surge of Amphan's scale changes in the future. We vary future sea level rise and population changes consistent with projections out to 2100, but keep other factors constant. Both India and Bangladesh will be negatively impacted, with India showing >200% increased exposure to extreme storm surge flooding (>3 m) under a high emissions scenario and Bangladesh showing an increase in exposure of >80% for low‐level flooding (>0.1 m). It is only when we follow a low‐emission scenario, consistent with the 2°C Paris Agreement Goal, that we see no real change in Bangladesh's storm surge exposure, mainly due to the population and climate signals cancelling each other out. For India, even with this low‐emission scenario, increases in flood exposure are still substantial (>50%). While here we attribute only the storm surge flooding component of the event to climate change, we highlight that tropical cyclones are multifaceted, and damages are often an integration of physical and social components. We recommend that future climate risk assessments explicitly account for potential compounding factors

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

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

Coastal Sea Level Monitoring in the Mediterranean and Black Seas

Spanning over a century, a traditional way to monitor sea level variability by tide gauges is – in combination with modern observational techniques like satellite altimetry – an inevitable ingredient in sea level studies over the climate scales and in coastal seas. The development of the instrumentation, remote data acquisition, processing and archiving in last decades allowed for extending the applications towards a variety of users and coastal hazard managers. The Mediterranean and Black50 seas are an example for such a transition – while having a long tradition for sea level observations with several records spanning over a century, the number of modern tide gauge stations are growing rapidly, with data available both in real-time and as a research product at different time resolutions. As no comprehensive survey of the tide gauge networks has been carried out recently in these basins, the aim of this paper is to map the existing coastal sea level monitoring infrastructures and the respective data availability. The survey encompasses description of major monitoring networks in the Mediterranean and Black55 seas and their characteristics, including the type of sea level sensors, measuring resolutions, data availability and existence of ancillary measurements, altogether collecting information about 236 presently operational tide gauge stations. The availability of the Mediterranean and Black seas sea level data in the global and European sea level repositories has been also screened and classified following their sampling interval and level of quality-check, pointing to the necessity of harmonization of the data available with different metadata and series at different repositories. Finally, an assessment of the networks’ capabilities60 for their usage in different sea level applications has been done, with recommendations that might mitigate the bottlenecks and assure further development of the networks in a coordinated way, being that more necessary in the era of the human-induced climate changes and the sea level ris