onglet

Articles

• The historical French heritage
  14 December 2010, by Frank

  France is very rich in systematic observations of coastal sea level over long time periods. The oldest (published) series of measurements were performed by the astronomers La Hire and Picard at Brest, France, in 1679, over about ten days. They repeated the experiment in 1692, over several months, again in Brest. Their aim was to study the tides and their results showed the fundamental importance of observation to understand and determine the characteristics of tides in a given place for the (…)

• A propos
  27 janvier 2020, par Médéric Gravelle

  La solution GNSS ’NGL14’ a été développée par le Nevada Geodetic Laboratory (NGL) en utilisant une stratégie de calcul PPP (Precise Point Positioning). Le logiciel de du Jet Propulsion Laboratory (JPL), GipsyX (version 1.0), a été utilisé pour produire des séries temporelles de positions journalières pour plus de 17,000 stations distribuées globalement grâce aux produits d’orbites et d’horloges du JPL exprimées dans le repère de référence IGS14 (Blewitt et al. 2018). La solution couvre la (…)

• About
  22 February 2017, by Mikaël Guichard

  In briefest terms, the approach consists in differencing the sea level time series from a tide gauge with an equivalent time series from satellite altimetry. To the extent that both instruments measure identical ocean signals, their difference is a proxy for the vertical position of the tide gauge. Assuming that the instrumental drifts are negligible, the time series of the sea level differences will then be dominated by vertical land motion at the tide gauge. This is illustrated in the (…)

• About
  8 January 2020, by Médéric Gravelle

  The GNSS solution named ’NGL14’ is produced by the Nevada Geodetic Laboratory (NGL) using a Precise Point Positioning (PPP) data analysis strategy. The GipsyX software (version 1.0) from the Jet Propulsion Laboratory (JPL) is employed to produce daily position time series for over 17,000 globally distributed stations using JPL satellite orbits and clock products expressed in the IGS14 reference frame (Blewitt et al. 2018). The data set covers the period January 1996 to March 2022.
  This (…)

• Statistiques
  27 janvier 2020, par Médéric Gravelle

  Champs de vitesse vertical Vitesses (robustes) estimées : 436 CGPS@TG 281 Moyenne des erreurs formelles : 0.42 mm/an Médiane des erreurs formelles : 0.32 mm/an

• Which observations ?
  16 February 2011, by Frank

  The tide gauge observations are heights of sea level expressed with respect to an arbitrary (conventional) and local datum. Hence, the term relative sea level is often used (relative to the land upon which the tide gauge is grounded).
  The sea level data available on SONEL are: daily mean sea levels obtained from different tidal filters (e.g., Doodson, Demerliac); monthly and annual mean sea levels, which contribute to the world data bank of the PSMSL.
  Other kinds of water levels are (…)

• Which GNSS solutions ?
  10 December 2010, by Frank

  – The processing of GPS observations is particularly complex for the calculation of vertical movements of the land on which the tide gauges are placed (movements of the order of mm/year). The article published in 2007 by the members of the consortium of the ‘ULR’ GPS analysis centre describes the difficulties and the challenges raised by this issue. The figure opposite illustrates the challenges : shown on the left is a series of average sea levels measured with tide gauges ; in the middle (…)

• Download
  27 May 2022, by Médéric Gravelle

  – Vertical velocities table
  The ULR7a_Vertical-Velocities_Table provides the vertical GPS velocities and uncertainties for the 546 stations fulfilling the criteria of 3 years of minimum length without discontinuities and with data gaps not exceeding 30%.
  The velocities come from the adjustment of both a functionnal and stochastic model, the latter accounting for a linear combination of white noise and power law process, whose parameters were estimated using the Restricted Maximum (…)

• About
  27 May 2022, by Médéric Gravelle

  The ULR7a GPS solution is a preliminary version of the reanalysis of 21 years of GPS data from 2000 to 2020 that has been undertaken within the framework of the 3rd data reprocessing campaign of the International GNSS Service (IGS). Its associated vertical velocity field is expressed in ITRF2014.
  Double-differenced ionosphere-free GPS carrier phase observations from daily regional (plus one global) networks of 546 stations were reanalyzed using a free-network strategy (station positions, (…)

• Results of the calibration tests
  10 December 2010, by Frank

  The results of the test measurements ’in situ’ are directly incorporated into the pages corresponding to the tide gauge in question. The test missions are generally the subject of a report in which the results of the use of the calibration measurements (Van de Casteele diagram) are published. Here is an example: test of the tide gauge at Socoa (Saint Jean-de-Luz) in May 2007.