Sea level measurement by GPS buoys: the multisensor experiment on Aix Island
A multi-sensor experiment was conducted on Aix Island on 27 and 28 March 2012. In this experiment organized by LIENSs, three organizations (CNRS/INSU, IPGP and SHOM) deployed buoys equipped with GPS antennas, designed to measure sea level. The water levels obtained with the buoys were compared to those provided by the RONIM permanent tide gauge (LIENSs, SHOM, CG17, Ile d'Aix) installed on the island to assess their accuracy. The first results show that the sea level data provided by these two types of instruments coincide.
Deployment of the 3 GPS buoys during the multi-device campaign organized by LIENSs at the RONIM tide gauge observatory on Aix Island. In the foreground: the RONIM tide gauge; in the background, left to right: the SHOM GNSS buoy, the IPGP GPS buoy, the LEGOS/DT-INSU GPS Buoy and Fort Boyard (Photo credits SHOM, S. Enet, March 2012). Click on the photo to enlarge.
Presentation of the multicomparison zone
On 27 and 28 March 2012, three prototype GPS buoys were deployed on Aix Island (Charente-Maritime), near the Barbotin pier in a relatively sheltered area some 10 meters deep near the permanent tide gauge and a tide staff to study the accuracy of this type of sensor for measuring sea level.
Ile d'Aix, a sea level observatory equipped with a radar tide gauge, a weather station and a permanent GPS station. Trajectories of the GPS buoys (photo source Géoportail, 2013 as amended). Click on the photo to enlarge.
Presentation of the GPS buoys and other devices
The three buoys with GPS antennas used in the experiment were independently developed by the CNRS/INSU (National Institute for Earth Sciences and Astronomy of the National Centre for Scientific Research), IPGP (Institute of Earth Physics of Paris) and SHOM (French Naval Hydrographic and Oceanographic Office).
Presentation of the three GPS buoys from left to right: the SHOM buoy, the CNRS/INSU buoy and the IPGP buoy. Click on the photo to enlarge.
Near the deployment area there is a permanent tide gauge observatory comprising a RONIM radar tide gauge (LIENSs, SHOM, CG17, Ile d'Aix) that transmits real-time sea level measurements and a tide staff. Also note that on March 28, water levels were measured manually over one tide cycle using the tide staff and an electric tape gauge. Additional measurements (not used later) were taken, including gravity, current meter and levelling measurements.
The GPS buoy data were processed in differential mode with respect to the ILDX reference station of the Permanent GNSS Network of IGN. First, the data from the reference station were processed in static mode using the GAMIT/GLOBK software by MIT (Herring et al., 2006) and secondly, the position of the buoys was estimated relative to the reference station using the TRACK software of the GAMIT/GLOBK software suite. The data were processed using the precise orbits of the International GNSS Service (IGS) with a cut-off angle of 10°. The L1 and L2 frequencies were used separately, which gives the best results for short baselines with respect to the ionosphere-free linear combination. Processing in differential mode assumes that the ionosphere and troposphere are identical at the reference station on land and the buoys.
Differences between the sea level measured by the buoys and the radar tide gauge. The ellipsoidal sea level height measured by the radar gauge is represented by the black line with the y-axis on the right - Click on image to enlarge
Different technologies for observing the sea level but the same level obtained within uncertainties
The Van de Casteele test is used to evaluate the performance of a tide gauge (IOC, 1985 Martin Miguez et al, 2008.). It involves the simultaneous measurement of the water level by the tide gauge being calibrated and the sensor used as a benchmark. The differences between the two measurements are calculated (ΔHe) and indicated on the X-axis while the ellipsoidal height of the sea level (He) is plotted on the Y axis. Assuming that the benchmark sensor provides accurate data, a vertical line centered at zero would indicate that the tide gauge tested also provides good data. In our case, the visual measurements taken on the tide staff on March 28 were used as a benchmark. Although rudimentary, this type of visual measurement taken by experienced operators in calm sea conditions can be very reliable.
Results of the Van de Casteele test for the three GPS buoys using the radar tide gauge as a benchmark - Click on image to enlarge
After checking the quality of the radar tide gauge measurements, it was used as a benchmark to evaluate the accuracy of the GPS buoy measurements. Several factors may explain the differences in height measured by the GPS buoys visible in the two figures above (André et al, 2013.):
- a levelling error of the height of the antenna relative to the surface of the water,
- the inclination of the IPGP buoy at low tide,
- differences in local dynamic topography due to wind and currents.
Despite these differences, the overall results show that the three buoys provide sea level measurements comparable to those of the radar tide gauge.
What comes next?
The encouraging results obtained in this experiment open up exciting new perspectives:
- Beyond the tide: the 1 Hz time series will be studied to assess the ability of the buoys to measure other phenomena in the supra-tidal frequency range such as seiches or waves.
- PPP treatment: the GPS data will be processed in PPP mode (Precise Point Positioning). This method is less accurate than the differential mode for short baselines, but it is extremely effective when the buoy is located far from a reference station. If this type of processing provides meaningful results, the use of this type of buoy would no longer be limited to coastal areas.
- André G, Martín Míguez B, Ballu V, Testut L, Wöppelmann G, 2013. Measuring sea-level with GPS-equipped buoys: A multi-instruments experiment at Aix Island. International Hydrographic Review, 27-38.
- Herring TA, King RW, McClusky SC, 2006. GAMIT: Reference Manual Version 10.34. Internal Memorandum, Massachusetts Institute of Technology, Cambridge
- IOC, 1985. Manual on sea-level measurement and interpretation. Volume I: Basic procedures. Intergovernmental Oceanographic Commission, Manuals & Guides No 14, 84 pp. (fr)
- Martín Míguez B, Le Roy R, Wöppelmann G, 2008. The use of radar tide gauges to measure the sea level along the French coast. Journal of Coastal Research, 24, 4C, 61-68.
To find out more:
- REFMAR instrumentation page: "Tide gauging by GNSS buoy"
- REFMAR application page "Height references"
- REFMAR page on the Aix Island tide gauge
- RONIM tide gauge network
- Poster "Measuring sea level with GPS-equipped buoys: a multi-instruments experiment at Aix island" presented at the Workshop commemorating the 80th anniversary of PSMSL in 2013
- Poster "Measuring sea level with GPS‐equipped buoys: a multicomparison experiment at Aix island" presented at the REFMAR Days 2013
- Rapport sur la caractérisation d'événements de tempêtes de l'automne-hiver 2013-2014 à partir des mesures marégraphiques
- Colloque - débat : réduire les risques littoraux et s'adapter au changement climatique La Rochelle 2-4 avril 2014
- New permanent tide gauge in Makemo - French Polynesia
- Impact of the storm Ulla on the sea level (14/02/2014)
- Report on the high tides and the effects of the low pressure system on 1 and 2 February and impact on sea level along the French Atlantic coast
- Annuaires des marées 2015 et SHOMAR édition 2014-2015 disponibles
- Sea level measurement by GPS buoys: the multisensor experiment on Aix Island
- coefficients des grandes marées 2014 calculées pour Brest
- egu 2014 sessions scientifiques s'appuyant sur les observations marégraphiques
- The effects of the low pressure system early this year on the sea level compared to other extreme events
- Compte rendu d'activité 2013 du GRGS
- Storms early this year and the impact on sea level in western France (2-5/01/2014)
- Impact of Cyclone Bejisa on sea level in Réunion Island (2 January 2014)
- SHOM BATHYELLI: new datum product referenced to the ellipsoid on data.shom.fr
- Offre de formation à l'information géographique maritime et littorale
- Impact of the storm Xaver in the North Sea on the sea level in the Nord-Pas de Calais region (5-6/12/2013)
- Document sur l'Analyse statistique des niveaux d'eau extrêmes - Environnements maritime et estuarien
- Offre de stage : surfaces de références verticales marines. Analyse à partir de l'altimétrie spatiale et des données marégraphiques
- Retour sur le workshop du PSMSL organisé en marge de la session des experts GLOSS
- Journées nationales génie côtier génie civil JNGCGC juillet 2014 Dunkerque
- Offre de stage : Caractérisation des seiches portuaires le long du littoral français
- French review of the 11thsession of the Intergovernmental Coordination Group for the Tsunami Warning and Mitigation System in the North-eastern Atlantic, Mediterranean and connected seas
- French review of the 13thsession of the GLOSS Group of Experts and workshop commemorating the 80th anniversary of PSMSL
- The reference work on the theory and practice of tides online (in French and in English
- Courants de surface : questionnaire d'évaluation des besoins des utilisateurs proposé par l'OHI
- nouvelle édition du produit RAM 2013 SHOM
- 13ème session groupe experts GLOSS et 80ème anniversaire PSMSL
- Vidéos en ligne changement climatique et niveau de la mer ; Vulnérabilité côtière et enjeux sociétaux
- REFMAR Days 2013: We thank the 134 participants
- Presentation of changes in sea level at the port of Brest since the beginning of the 18th century at the REFMAR Days
- Deployment of a new RONIM tide gauge observatory in Port-la-Nouvelle (Mediterranean - Aude)
- Rapport annuel d'activité 2012 REFMAR
- Nouvelle fiche technique REFMAR Description d'une fiche d'observatoire de marée FOM
- Compte rendu d'activité 2012 du GRGS
- Languedoc Roussillon DREAL: producer of tidal observations and new partner of REFMAR
- coefficients de marée 2013
- Statistiques 2012 des niveaux marins extrêmes des côtes de France (Manche et Atlantique)
- Colloque coastal dynamics 2013
- Tidal observations of the tsunami generated by the earthquake off the Solomon Islands (Pacific Ocean) on February 6, 2013
- Colloque Hausse du niveau de la mer et risques côtiers - ANR CECILE
- Annonce 14eme Congres Francais de Sedimentologie
- Plan de mise en oeuvre 2012 du programme GLOSS
- Offre d'emploi docteur ou ingénieur chargé d'étude en reconstruction et analyse d'une série historique du niveau de la mer
- EGU 2013 sessions scientifiques s'appuyant sur les observations marégraphiques
- Offre stage estimation de l'évolution du niveau moyen de la mer à partir des mesures marégraphiques
- Colloque Evénements extrêmes d’inondation SHF
- Un grand pas pour le système d’alerte aux tsunamis dans l’Atlantique du Nord-Est et la Méditerranée
- Report on the 9th session of the Intergovernmental Coordination Group for the Tsunami Early Warning System in the North-eastern Atlantic and Mediterranean
- International Conference on the digitization and preservation of analogue archives, including tidal archives
- Observation of a meteotsunami on July 27, 2012 in the Western Mediterranean
- Scientific presentations concerning variations in sea level, organized on line by the CNFGG
- Tidal predictions available using Android
- The French President visits the tide gauge stand at Tonnerres de Brest 2012
- Tide gauging technology at Tonnerres de Brest 2012
- 2011 Annual Report of REFMAR activity on lineEFMAR
- Tsunami alert centre (CENALT) operational
- Dissertation of Mr. Thomas Gouriou:
- Coordinating tsunami alerts in the Lesser Antilles (Source DEAL Guadeloupe)
- XIIème Journées Nationales Génie Côtier Génie Civil à Cherbourg
- Deployment of a new tide gauge observatory on the island of Saint-Pierre (Islands of Saint Pierre and Miquelon)
- Deployment of a new tide gauge observatory on Maré in New Caledonia (Maré in the Loyalty Islands)
- 9ème édition des journées scientifiques et techniques du CETMEF
- Pumping of freshwater partly to blame for the rise in sea levels
- Programme de recherche japonais sur des radars à tsunamis
- French assessment of the 7th meeting of the intergovernmental coordination group on the tsunami alert system in the Caribbean, under the auspices of UNESCO
- Effects on sea level measurement of the earthquakes occurring off the coast of Sumatra on 11 April 2012
- Installation of a new tide gauge at Port Ferréol (Les Issambres)
- An exceptional rise in sea levels revealed
- Publication of Volume 3 of the "The climate of France in the 21st century" series concerning the change in the sea level (MEDDTL / ONERC)
- Inventory action concerning the sea level data in Corsica
- EGU 2012
- Evolution des composantes du niveau marin en charente-maritime : soutenance de thèse
- Nouveau portlet REFMAR : le puits de tranquillisation
- Variations in the sea level along the length of the Western Tropical Pacific Islands
- Rapport d'activité quinquennal du GRGS 2007-2011
- Demi-journée scientifique organisée par le CNFGG portant sur les variations du niveau de la mer - 6 mars - Paris
- 34es journées de l'hydraulique portant sur les événements extrêmes fluviaux et maritimes - 1 et 2 février - Paris
- Assises nationales des risques naturels 2012 - 19 et 20 janvier - Bordeaux
- Tide gauge data exchange day in France within the framework of the CRATANEM project
- Inventory action concerning historical sea level data in paper format
- EGU 2012
- Coefficients de marée 2012
- Effect of the passage of cyclone Andrea on the sea level in France (5-6/01/2012)
- New edition of the Maritime Altimetric References (RAM) product
- Report of the GIC/SATANEM in Santander, Spain - 22-24/11/2011
- French assessment of the 12th session of the GLOSS Group of Experts and associated workshops
- Sea level observations: a major cog in the establishment of a storm surge flooding warning system
- 12th session of the GLOSS Group of Experts and associated workshops [7-11/11/2011]
- XIIèmes journées nationales Génie Côtier - Génie Civil à Cherbourg
- Special edition of the 'Annales hydrographiques' hydrographic review dedicated to the observation and study of the sea level
- Slow subsidence of the island of Tahiti detected using, in particular, tide gauge data
- Janvier 2012 : Première édition des Assises nationales des risques naturels
- The sea level : Principal measure of the French plan for adapting to climate change
- Conférence : Have we reason to fear an increase in the level of the tide ?
- Observation of the mini-tsunami off Cornwall on 27 June by French tide gauges.
- Installation of a new tide gauge in New-Caledonia on the island of Lifou
- Very low tides on Monday 21 March 2011
- Low tide on the beaches of the west coast of La Réunion
- Installation of two tide gauges in New Caledonia
- Centenary of the SHF: Exterme maritime and fluvial events
- Installation of two new tide gauges at Ile Rousse in Corsica and in the port of La Figueirette (Théoule-sur-Mer)
- IAPSO Commission on Mean Sea Level
- Monitoring the tide gauges of the Marseille observatory
- Symposium on Vulnerability of Coastal ecosystems to global change and extreme events - At the crossroads of knowledge to the benefit of coastal and marine ecosystem services
- Conférence sur l'océanographie cotière operationnelle
- Modernisation of the tide gauge at Port-Tudy (Ile de Groix)
- Installation of a new tide gauge observatory on the Ile d'Aix
- Observations of the trans-Pacific tsunami on 11 March 2011 by the French Polynesia and New Caledonia tide gauges.
- Seiche in the port of Royan during the night of 15 to 16 February 2011
- Les multiples facettes du changement climatique (SMF)
- EGU 2011
- Summary of the Proceedings of the Seminar on Impacts of Climate Change on Coastal Risk organised by the BRGM in November 2010
- Issue of the new SHOMAR - Tidal predictions
- Article relating to observations of sea levels at Saint-Paul Island (Indian / Southern Ocean)
- Network of tide gauges in the Pacific
- Installation of a new tide gauge in Monaco
- Installation of two new tide gauges in Corsica at Centuri and Solenzara
- 4th Workshop on Coastal Altimetry and OST-ST Meeting on Altimetry for Oceans and Hydrology
- Seminar on Impact of Climate Change on Coastal Risks
- Coastal areas at a time of climate change
- Draft plan for preventing marine inundation and flas floods
- Installation of a RONIM tide gauge at Fos-sur-Mer
- National coordination for the observation of sea levels
- Installation of a tide gauge at Toamasina
- Height of water observed by SHOM during the passage of storm Xynthia
- Installation of a tide gauge in Mayotte for the tsunami warning system in the Indian Ocean
- SHOM will take part in setting up a tsunami warning system
- Brest tide gauge : 300 years of observation
- Digitizing, transforming and validating paper records of sea level variations, called marigrams by NUNIEAU
- Radar tide gauges in France and monitoring of tide gauge-performance
- Modernisation Toulon and Nice tide gauges on 20 and 26 mai 2008