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Validation of marine geoid models by utilizing hydrodynamic model and shipborne GNSS profiles / Sander Varbla in Marine geodesy, Vol 43 n° 2 (March 2020)  

Public [article]  inMarine geodesy > Vol 43 n° 2 (March 2020) . - pp 134 - 162 Titre : Validation of marine geoid models by utilizing hydrodynamic model and shipborne GNSS profiles Type de document : Article/Communication Auteurs : Sander Varbla, Auteur ; Artu Ellmann, Auteur ; Nicole Delpeche-Ellmann, Auteur Année de publication : 2020 Article en page(s) : pp 134 - 162 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes descripteurs IGN] Baltique, mer [Termes descripteurs IGN] données marégraphiques [Termes descripteurs IGN] force de gravitation [Termes descripteurs IGN] geoïde marin [Termes descripteurs IGN] instrument embarqué [Termes descripteurs IGN] instrumentation GNSS [Termes descripteurs IGN] levé gravimétrique [Termes descripteurs IGN] navire [Termes descripteurs IGN] niveau de la mer [Termes descripteurs IGN] simulation hydrodynamique Résumé : (auteur) An essential role of the FAMOS international cooperation project is to obtain new marine gravity observations over the Baltic Sea for improving gravimetric geoid modelling. To achieve targeted 5 cm modelling accuracy, it is important to acquire new gravimetric data, as the existing data over some regions are inaccurate and sparse. As the accuracy of contemporary geoid models over marine areas remains unknown, it is important to evaluate geoid modelling outcome by independent data. Thus, this study presents results of a shipborne marine gravity and GNSS campaign for validation of existing geoid models conducted in the eastern section of the Baltic Sea. Challenging aspects for utilizing shipborne GNSS profiles tend to be with quantifying vessel’s attitude, processing of noise in the data and referencing to the required datum. Consequently, the novelty of this study is in the development of methodology that considers the above-mentioned challenges. In addition, tide gauge records in conjunction with an operational hydrodynamic model are used to identify offshore sea level dynamics during the marine measurements. The results show improvements in geoid modelling due to new marine gravimetric data. It is concluded that the marine GNSS profiles can potentially provide complementary constraints in problematic geoid modelling areas. Numéro de notice : A2020-051 Thématique : POSITIONNEMENT Nature : Article DOI : 10.1080/01490419.2019.1701153 date de publication en ligne : 20/01/2020 En ligne : https://doi.org/10.1080/01490419.2019.1701153 Format de la ressource électronique : url article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=94918 [article]

On the assimilation of absolute geodetic dynamic topography in a global ocean model: impact on the deep ocean state / Alexey Androsov in Journal of geodesy, vol 93 n° 2 (February 2019)  

Public [article]  inJournal of geodesy > vol 93 n° 2 (February 2019) . - pp 141 - 157 Titre : On the assimilation of absolute geodetic dynamic topography in a global ocean model: impact on the deep ocean state Type de document : Article/Communication Auteurs : Alexey Androsov, Auteur ; Lars Nerger, Auteur ; Reiner Schnur, Auteur ; Alberta Albertella, Auteur ; Reiner Rummel, Auteur ; et al., Auteur Année de publication : 2019 Article en page(s) : pp 141 - 157 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes descripteurs IGN] assimilation des données [Termes descripteurs IGN] circulation océanique [Termes descripteurs IGN] données altimétriques [Termes descripteurs IGN] données CHAMP [Termes descripteurs IGN] données GOCE [Termes descripteurs IGN] données GRACE [Termes descripteurs IGN] filtre de Kalman [Termes descripteurs IGN] geoïde marin [Termes descripteurs IGN] géoïde terrestre [Termes descripteurs IGN] hauteurs de mer [Termes descripteurs IGN] modèle de simulation [Termes descripteurs IGN] modèle océanographique [Termes descripteurs IGN] océanographie dynamique [Termes descripteurs IGN] salinité [Termes descripteurs IGN] température de surface de la mer Résumé : (auteur) General ocean circulation models are not perfect. Forced with observed atmospheric fluxes they gradually drift away from measured distributions of temperature and salinity. We suggest data assimilation of absolute dynamical ocean topography (DOT) observed from space geodetic missions as an option to reduce these differences. Sea surface information of DOT is transferred into the deep ocean by defining the analysed ocean state as a weighted average of an ensemble of fully consistent model solutions using an error-subspace ensemble Kalman filter technique. Success of the technique is demonstrated by assimilation into a global configuration of the ocean circulation model FESOM over 1 year. The dynamic ocean topography data are obtained from a combination of multi-satellite altimetry and geoid measurements. The assimilation result is assessed using independent temperature and salinity analysis derived from profiling buoys of the AGRO float data set. The largest impact of the assimilation occurs at the first few analysis steps where both the model ocean topography and the steric height (i.e. temperature and salinity) are improved. The continued data assimilation over 1 year further improves the model state gradually. Deep ocean fields quickly adjust in a sustained manner: A model forecast initialized from the model state estimated by the data assimilation after only 1 month shows that improvements induced by the data assimilation remain in the model state for a long time. Even after 11 months, the modelled ocean topography and temperature fields show smaller errors than the model forecast without any data assimilation. Numéro de notice : A2019-076 Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-018-1151-1 date de publication en ligne : 12/05/2018 En ligne : https://doi.org/10.1007/s00190-018-1151-1 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=92190 [article]

Using models of the ocean's mean dynamic topography to identify errors in coastal geodetic levelling / M. S. Filmer in Marine geodesy, vol 37 n° 1 (March - May 2014)  

Public [article]  inMarine geodesy > vol 37 n° 1 (March - May 2014) . - pp 47 - 64 Titre : Using models of the ocean's mean dynamic topography to identify errors in coastal geodetic levelling Type de document : Article/Communication Auteurs : M. S. Filmer, Auteur Année de publication : 2014 Article en page(s) : pp 47 - 64 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Nivellement [Termes descripteurs IGN] données GNSS [Termes descripteurs IGN] geoïde marin [Termes descripteurs IGN] littoral [Termes descripteurs IGN] niveau moyen des mers [Termes descripteurs IGN] nivellement géodésique [Termes descripteurs IGN] quasi-géoïde [Termes descripteurs IGN] trait de côte Résumé : (Auteur) Identifying errors (blunders and systematic errors) in coastal geodetic levelling networks has often been problematic, primarily for two reasons. First, mean sea level (MSL) at tide gauges cannot be directly compared to height differences from levelling because the geoid/quasigeoid and MSL are not parallel, being separated by the ocean's mean dynamic topography (MDT). Second, there is a the lack of redundancy at the edge of the levelling network. This article sets out a methodology to independently identify blunders and/or systematic errors (over long distances) in geodetic levelling using MDT models to account for the separation between the geoid/quasigeoid and MSL at tide gauges. This method is then tested in a case study using an oceanographic MDT model, MSL observations, GNSS data, and a quasigeoid model. The results are significant because the errors found could not be detected by standard levelling misclosure checks alone, with supplementary data from an MDT model, with cross-validation from GNSS-quasigeoid allowing their detection. In addition, it appears that an oceanographic-only MDT is as effective as GNSS and a quasigeoid model for detecting levelling errors, which could be particularly useful for countries with coastal levelling errors in their levelling networks that cannot be identified by conventional levelling closure checks. Numéro de notice : A2015-163 Thématique : POSITIONNEMENT Nature : Article DOI : 10.1080/01490419.2013.868383 date de publication en ligne : 29/10/2010 En ligne : https://doi.org/10.1080/01490419.2013.868383 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=75850 [article]

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Lowest astronomical tide in the North Sea derived from a vertically referenced shallow water model, and an assessment of its suggested sense of safety / D. Slobbe in Marine geodesy, vol 36 n° 1 (January - March 2013)  

Public [article]  inMarine geodesy > vol 36 n° 1 (January - March 2013) . - pp 31 - 71 Titre : Lowest astronomical tide in the North Sea derived from a vertically referenced shallow water model, and an assessment of its suggested sense of safety Type de document : Article/Communication Auteurs : D. Slobbe, Auteur ; R. Klees, Auteur ; M. Verlaan, Auteur ; et al., Auteur Année de publication : 2013 Article en page(s) : pp 31 - 71 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Océanographie [Termes descripteurs IGN] géoïde local [Termes descripteurs IGN] geoïde marin [Termes descripteurs IGN] marée océanique [Termes descripteurs IGN] niveau de la mer [Termes descripteurs IGN] niveau moyen des mers [Termes descripteurs IGN] Nord, mer du [Termes descripteurs IGN] réduction Résumé : (Auteur) Water level reduction with global navigation satellite systems in bathymetric surveying requires knowledge of the ellipsoidal heights of lowest astronomical tide (LAT). The traditional approach uses tidal water levels of an ocean tide model, which are subtracted from mean sea level (MSL). This approach has two major drawbacks: the modeled water levels refer to an equipotential surface, which differs from MSL, and MSL may not be known close to the coast. Here, we propose to model LAT directly relative to an equipotential surface (geoid). This is conceptually consistent with the flow equations and allows the inclusion of temporal MSL variations into the LAT definition. Numerical experiments for the North Sea show that significant differences between the traditional and the pursued approach exist if average monthly variations in MSL are included. A validation of the modeled LAT using tide gauge records reveals systematic errors, which we attribute to both the model and the tidal analysis procedure. We also show that the probability that water levels drop below LAT is high, with maximum frequency of once per week in the eastern North Sea. Therefore, we propose to reconsider the deterministic concept of LAT by a probabilistic chart datum concept, and we quantified the differences between them. Numéro de notice : A2013-245 Thématique : POSITIONNEMENT Nature : Article DOI : 10.1080/01490419.2012.743493 date de publication en ligne : 13/03/2013 En ligne : https://doi.org/10.1080/01490419.2012.743493 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=32383 [article]

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Assessment of systematic errors in the computation of gravity gradients from satellite altimeter data / Johannes Bouman in Marine geodesy, vol 34 n° 2 (April - June 2011)  

Public [article]  inMarine geodesy > vol 34 n° 2 (April - June 2011) . - pp 85 - 107 Titre : Assessment of systematic errors in the computation of gravity gradients from satellite altimeter data Type de document : Article/Communication Auteurs : Johannes Bouman, Auteur ; W. Bosch, Auteur ; J. Sebera, Auteur Année de publication : 2011 Article en page(s) : pp 85 - 107 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes descripteurs IGN] altimétrie satellitaire par radar [Termes descripteurs IGN] champ de pesanteur terrestre [Termes descripteurs IGN] données altimétriques [Termes descripteurs IGN] données GOCE [Termes descripteurs IGN] erreur systématique [Termes descripteurs IGN] geoïde marin [Termes descripteurs IGN] gradient de gravitation [Termes descripteurs IGN] océanographie dynamique Résumé : (Auteur) With satellite radar altimetry, the oceanic geoid can be determined with high precision and resolution. Double differentiation of these data along satellite altimeter ground tracks yields along-track gravity gradients that can be used to compute vertical gravity gradients at ground track crossovers. One way to counteract the noise amplification due to the differentiation is to smooth the data using smoothing splines. Although the effect of satellite altimeter data noise has been investigated to some extent, the associated systematic errors have not been assessed so far. Here we show that some of the systematic errors cannot be neglected. In particular, we found that the negligence of the dynamic ocean topography (DOT) may introduce errors that are greater than the measurement noise induced errors. If the gravity gradients are to be used for GOCE validation, then also in this case the DOT may not be neglected as the signal at GOCE altitude of 260 km may be above the GOCE requirements. In addition, we show that the altimetry derived gravity gradients cannot be compared one-to-one with those in a local Cartesian frame. The differences are small compared with the total signal, but they may be larger than the satellite altimetry induced stochastic errors and may be above the GOCE requirements. The cubic splines second derivative truncation error requires the use of 10 Hz altimeter data for the computation of gravity gradients at the Earth's surface, while 1 Hz data are sufficient for validation at GOCE altitude. Numéro de notice : A2011-409 Thématique : POSITIONNEMENT Nature : Article DOI : 10.1080/01490419.2010.518498 date de publication en ligne : 16/05/2011 En ligne : https://doi.org/10.1080/01490419.2010.518498 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=31188 [article]

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Sea surface topography and marine geoid by airborne laser altimetry and shipborne ultrasound altimetry / Philippe Limpach (2010)  

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Taking the measure of Earth / J. Benveniste in ESA bulletin, n° 128 (November 2006)  

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Determination of evolution of the altimetric mean level of western mediterranean from the Jason-1 Data: comparison with analysis of the tidal gauge measurements / M. Haddad in Bulletin des sciences géographiques, n° 18 (octobre 2006)

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La Terre vue de l'espace / Anny Cazenave (2004)

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Third ERS Symposium on space at the service of our environment, Florence, Italy, 14 - 21 March 1997, 3. Volume 3 / T.D. Guyenne (1997)

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Ajustement des profils altimétriques : minimisation des écarts aux noeuds / J.P. Bariot (1985)

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