Mean sea level is a vague notion that needs to be clearly defined to have a good understanding of the signals contained in the series of values and to interpret the variations (temporal mean? spatial mean? in what extension?).
The definition adopted in SONEL corresponds to the definition of the Permanent Service for Mean Sea Level, the PSMSL, and of the Global Sea Level Observing System GLOSS to which SONEL contributes. The means are temporal averages at the tide gauges (point on the coast), over daily, monthly and annual periods.
There are, however, different ways to calculate these means. They are briefly summarised below:
Annual values: arithmetic means of monthly means weighted for the number of days actually observed during the month. The value is calculated if at least 11 monthly values are actually available (cf. rules of the PSMSL).
Monthly values : arithmetic means of daily means. However, the value is not calculated if more than 15 days are missing (cf. rules of the PSMSL).
Daily values: the choice of an arithmetic mean over a 24h period has the disadvantage that it does not adequately filter the signals from periods of less than one day, particularly those from tides for which a period of 24h50 would be more suitable. Filters have been designed to do this (Doodson, Demerliac). Pugh (1987) reexamined the different filters and concluded that the differences were minimal for the monthly means at Newlyn (1-2 mm). We have adopted the Demerliac filter for historical reasons, but the Doodson filter is proposed to the users as well. Click on the link to find out more about filters.
The daily, monthly and annual heights are expressed in millimetres.
The dates are in decimal years (centred on the 15th day of the month for monthly values and at midday for daily values).
If you have a relevant reference to suggest, please send-us an e-mail : firstname.lastname@example.org
André, 2013.Measuring sea level with GPS-equipped buoys: a multi-instruments experiement at Aix Island. International Hydrographic Review.
Gobron, de-Viron et al., 2019.Assessment of tide gauges biases and precisions by the combination of multiple co-located time series. Journal of Atmospheric and Oceanic Technology.
Gouriou, 2013.Reconstruction of a two-century long sea level record for the Pertuis d'Antioche (France). Continental Shelf Research.
Gouriou, 2012.Evolution des composantes du niveau marin à partir d'observations de marégraphie effectuées depuis la fin du 18ème siècle en Charente-Maritime. Université de la Rochelle.
Vu, Frappart et al., 2018.Multi-Satellite Altimeter Validation along the French Atlantic Coast in the Southern Bay of Biscay from ERS-2 to SARAL. Remote Sensing.
Tempête Amélie le Dimanche 3 novembre au matin. Vents jusqu'à 130 km/H.
Work in progress at the tide gauge jetty to install a power cable, mew lights, etc... This is done with high pressure water. The work started in October 2019 and should be ended by January/February 2020.
Storm at Aix island 'Miguel'. Starting at 06:00 UTC day 158 and shall continue until 12:00 UTC day 158. Exceptional for this period of the year. Tide gauge records at 1 Hz are logged at ULR. Expected gust 120 km/h. E.Poirier
Juin 2017 - DDTM intervient dans l'enceinte du marégraphe (29/06/2017)
Etienne Poirier a été contacté par Pierre Durand de Gevigney du Département de La Charente-Maritime pour accéder à l'enceinte du marégraphe sur la jetée Barbotin. Ceci afin de démonter un garde corps pour faire des mesures d'épaisseur de métal afin de décider du comment de la rénovation des garde corps de la jetée. L'intervention a été réalisée le .... sans présence de SONEL. Ils ont utilisé de double de clés situées au local du club nautique.