Centre de documentation
scientifique

Dépouillements

Reliability of partial ambiguity fixing with multiple GNSS constellations / J. Wang in Journal of geodesy, vol 87 n° 1 (January 2013)  

Public [article]  inJournal of geodesy > vol 87 n° 1 (January 2013) . - pp 1 - 14 Titre : Reliability of partial ambiguity fixing with multiple GNSS constellations Type de document : Article/Communication Auteurs : J. Wang, Auteur ; Y. Feng, Auteur Année de publication : 2013 Article en page(s) : pp 1 - 14 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes IGN] matrice [Termes IGN] positionnement cinématique en temps réel [Termes IGN] résolution d'ambiguïté [Termes IGN] traitement de données GNSS Résumé : (Auteur) Reliable ambiguity resolution (AR) is essential to real-time kinematic (RTK) positioning and its applications, since incorrect ambiguity fixing can lead to largely biased positioning solutions. A partial ambiguity fixing technique is developed to improve the reliability of AR, involving partial ambiguity decorrelation (PAD) and partial ambiguity resolution (PAR). Decorrelation transformation could substantially amplify the biases in the phase measurements. The purpose of PAD is to find the optimum trade-off between decorrelation and worst-case bias amplification. The concept of PAR refers to the case where only a subset of the ambiguities can be fixed correctly to their integers in the integer least squares (ILS) estimation system at high success rates. As a result, RTK solutions can be derived from these integer-fixed phase measurements. This is meaningful provided that the number of reliably resolved phase measurements is sufficiently large for least-square estimation of RTK solutions as well. Considering the GPS constellation alone, partially fixed measurements are often insufficient for positioning. The AR reliability is usually characterised by the AR success rate. In this contribution, an AR validation decision matrix is firstly introduced to understand the impact of success rate. Moreover the AR risk probability is included into a more complete evaluation of the AR reliability. We use 16 ambiguity variance–covariance matrices with different levels of success rate to analyse the relation between success rate and AR risk probability. Next, the paper examines during the PAD process, how a bias in one measurement is propagated and amplified onto many others, leading to more than one wrong integer and to affect the success probability. Furthermore, the paper proposes a partial ambiguity fixing procedure with a predefined success rate criterion and ratio test in the ambiguity validation process. In this paper, the Galileo constellation data is tested with simulated observations. Numerical results from our experiment clearly demonstrate that only when the computed success rate is very high, the AR validation can provide decisions about the correctness of AR which are close to real world, with both low AR risk and false alarm probabilities. The results also indicate that the PAR procedure can automatically chose adequate number of ambiguities to fix at given high-success rate from the multiple constellations instead of fixing all the ambiguities. This is a benefit that multiple GNSS constellations can offer. Numéro de notice : A2013-069 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-012-0573-4 Date de publication en ligne : 12/06/2012 En ligne : https://doi.org/10.1007/s00190-012-0573-4 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=32207 [article]

Exemplaires(1)

Code-barres	Cote	Support	Localisation	Section	Disponibilité
266-2013011	SL	Revue	Centre de documentation	Revues en salle	Disponible

The height datum problem and the role of satellite gravity models / A. Gatti in Journal of geodesy, vol 87 n° 1 (January 2013)  

Public [article]  inJournal of geodesy > vol 87 n° 1 (January 2013) . - pp 15 - 22 Titre : The height datum problem and the role of satellite gravity models Type de document : Article/Communication Auteurs : A. Gatti, Auteur ; M. Reguzzoni, Auteur ; Giovanna Venuti, Auteur Année de publication : 2013 Article en page(s) : pp 15 - 22 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] altitude normale [Termes IGN] anomalie de pesanteur [Termes IGN] données GOCE [Termes IGN] données GRACE [Termes IGN] Earth Gravity Model 2008 [Termes IGN] erreur en altitude [Termes IGN] erreur systématique [Termes IGN] géoïde altimétrique [Termes IGN] hauteur ellipsoïdale [Termes IGN] modèle de géopotentiel [Termes IGN] niveau moyen des mers [Termes IGN] réseau de nivellement [Termes IGN] système de référence altimétrique Résumé : (Auteur) Regional height systems do not refer to a common equipotential surface, such as the geoid. They are usually referred to the mean sea level at a reference tide gauge. As mean sea level varies (by +1 to 2 m) from place to place and from continent to continent each tide gauge has an unknown bias with respect to a common reference surface, whose determination is what the height datum problem is concerned with. This paper deals with this problem, in connection to the availability of satellite gravity missions data. Since biased heights enter into the computation of terrestrial gravity anomalies, which in turn are used for geoid determination, the biases enter as secondary or indirect effect also in such a geoid model. In contrast to terrestrial gravity anomalies, gravity and geoid models derived from satellite gravity missions, and in particular GRACE and GOCE, do not suffer from those inconsistencies. Those models can be regarded as unbiased. After a review of the mathematical formulation of the problem, the paper examines two alternative approaches to its solution. The first one compares the gravity potential coefficients in the range of degrees from 100 to 200 of an unbiased gravity field from GOCE with those of the combined model EGM2008, that in this range is affected by the height biases. This first proposal yields a solution too inaccurate to be useful. The second approach compares height anomalies derived from GNSS ellipsoidal heights and biased normal heights, with anomalies derived from an anomalous potential which combines a satellite-only model up to degree 200 and a high-resolution global model above 200. The point is to show that in this last combination the indirect effects of the height biases are negligible. To this aim, an error budget analysis is performed. The biases of the high frequency part are proved to be irrelevant, so that an accuracy of 5 cm per individual GNSS station is found. This seems to be a promising practical method to solve the problem. Numéro de notice : A2013-070 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-012-0574-3 Date de publication en ligne : 03/07/2012 En ligne : https://doi.org/10.1007/s00190-012-0574-3 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=32208 [article]

Exemplaires(1)

Code-barres	Cote	Support	Localisation	Section	Disponibilité
266-2013011	SL	Revue	Centre de documentation	Revues en salle	Disponible

Estimation of mass change trends in the Earth’s system on the basis of GRACE satellite data, with application to Greenland / C. Siemes in Journal of geodesy, vol 87 n° 1 (January 2013)  

Public [article]  inJournal of geodesy > vol 87 n° 1 (January 2013) . - pp 69 - 87 Titre : Estimation of mass change trends in the Earth’s system on the basis of GRACE satellite data, with application to Greenland Type de document : Article/Communication Auteurs : C. Siemes, Auteur ; Pavel Ditmar, Auteur ; et al., Auteur Année de publication : 2013 Article en page(s) : pp 69 - 87 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] bilan de masse [Termes IGN] calotte glaciaire [Termes IGN] champ de pesanteur terrestre [Termes IGN] données GRACE [Termes IGN] filtre de Wiener [Termes IGN] gravimétrie spatiale [Termes IGN] Groenland [Termes IGN] harmonique sphérique [Termes IGN] isostasie [Termes IGN] levé gravimétrique [Termes IGN] matrice de covariance Résumé : (Auteur) The Gravity Recovery and Climate Experiment (GRACE) satellite mission measures the Earth’s gravity field since March 2002. We propose a new filtering procedure for post-processing GRACE-based monthly gravity field solutions provided in the form of spherical harmonic coefficients. The procedure is tuned for the optimal estimation of linear trends and other signal components that show a systematic behavior over long time intervals. The key element of the developed methodology is the statistically optimal Wiener-type filter which makes use of the full covariance matrices of noise and signal. The developed methodology is applied to determine the mass balance of the Greenland ice sheet, both per drainage system and integrated, as well as the mass balance of the ice caps on the islands surrounding Greenland. The estimations are performed for three 2-year time intervals (2003–2004, 2005–2006, and 2007–2008), as well as for the 6-year time interval (2003–2008). The study confirms a significant difference in the behavior of the drainage systems over time. The average 6-year rate of mass loss in Greenland is estimated as 165 + 15 Gt/year. The rate of mass loss of the ice caps on Ellesmere Island (together with Devon Island), Baffin Island, Iceland, and Svalbard is found to be 22 + 4, 21 + 6, 17 + 9, and 6 + 2 Gt/year, respectively. All these estimates are corrected for the effect of glacial isostatic adjustment. Numéro de notice : A2013-071 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-012-0580-5 Date de publication en ligne : 12/07/2012 En ligne : https://doi.org/10.1007/s00190-012-0580-5 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=32209 [article]

Exemplaires(1)

Code-barres	Cote	Support	Localisation	Section	Disponibilité
266-2013011	SL	Revue	Centre de documentation	Revues en salle	Disponible

Analysis of the repeated absolute gravity measurements in the Czech Republic, Slovakia and Hungary from the period 1991–2010 considering instrumental and hydrological effects / S. Zhang in Journal of geodesy, vol 87 n° 1 (January 2013)  

Public [article]  inJournal of geodesy > vol 87 n° 1 (January 2013) . - pp 29 - 42 Titre : Analysis of the repeated absolute gravity measurements in the Czech Republic, Slovakia and Hungary from the period 1991–2010 considering instrumental and hydrological effects Type de document : Article/Communication Auteurs : S. Zhang, Auteur ; X. Tong, Auteur ; K. Zhang, Auteur Année de publication : 2013 Article en page(s) : pp 29 - 42 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] analyse diachronique [Termes IGN] erreur instrumentale [Termes IGN] gravimètre absolu [Termes IGN] Hongrie [Termes IGN] hydrologie [Termes IGN] levé gravimétrique [Termes IGN] République Tchèque [Termes IGN] Slovaquie Résumé : (Auteur) Since August 2001, the absolute gravimeter FG5#215 has been used for the modernization of the national gravity networks of the Czech Republic, Slovakia, and Hungary. Altogether 43 absolute stations were measured, some of them repeatedly. Absolute gravity at 29 stations had already been determined in 1990s by other absolute gravimeters (FG5 or JILAg). Differences of repeated measurements at most of the stations show an unexpected decrease of gravity (up to 22 uGal) over the whole region. An uncertainty assessment of absolute measurements with a special emphasis put on hydrological effects shows a statistical significance of the detected gravity variations at many stations. In this manuscript, three possible reasons of such findings are discussed: (1) a regional geodynamic activity, (2) systematic instrumental errors (offsets), (3) hydrological effects. The analysis and statistics of the gravity differences in context of international comparisons of absolute gravimeters show offsets up to 9 uGal related to data of the JILAg-6 and FG5#107 gravimeters. Data collected in this study demonstrate that considering instrumental and hydrological effects on gravity are crucial for a correct interpretation of repeated absolute gravity measurements. Numéro de notice : A2013-072 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-012-0576-1 Date de publication en ligne : 24/06/2012 En ligne : https://doi.org/10.1007/s00190-012-0576-1 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=32210 [article]

Exemplaires(1)

Code-barres	Cote	Support	Localisation	Section	Disponibilité
266-2013011	SL	Revue	Centre de documentation	Revues en salle	Disponible

Algorithms for geodesics / C. Karney in Journal of geodesy, vol 87 n° 1 (January 2013)  

Public [article]  inJournal of geodesy > vol 87 n° 1 (January 2013) . - pp 43 - 55 Titre : Algorithms for geodesics Type de document : Article/Communication Auteurs : C. Karney, Auteur Année de publication : 2013 Article en page(s) : pp 43 - 55 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie [Termes IGN] ellipsoïde de révolution [Termes IGN] géodésie mathématique [Termes IGN] polygone [Termes IGN] projection gnomonique Résumé : (Auteur) Algorithms for the computation of geodesics on an ellipsoid of revolution are given. These provide accurate, robust, and fast solutions to the direct and inverse geodesic problems and they allow differential and integral properties of geodesics to be computed. Numéro de notice : A2013-073 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-012-0578-z Date de publication en ligne : 26/06/2012 En ligne : https://doi.org/10.1007/s00190-012-0578-z Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=32211 [article]

Exemplaires(1)

Code-barres	Cote	Support	Localisation	Section	Disponibilité
266-2013011	SL	Revue	Centre de documentation	Revues en salle	Disponible

Global height system unification with GOCE: a simulation study on the indirect bias term in the GBVP approach / C. Gerlach in Journal of geodesy, vol 87 n° 1 (January 2013)  

Public [article]  inJournal of geodesy > vol 87 n° 1 (January 2013) . - pp 57 - 67 Titre : Global height system unification with GOCE: a simulation study on the indirect bias term in the GBVP approach Type de document : Article/Communication Auteurs : C. Gerlach, Auteur ; Reiner Rummel, Auteur Année de publication : 2013 Article en page(s) : pp 57 - 67 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie physique [Termes IGN] altitude [Termes IGN] anomalie de pesanteur [Termes IGN] données GOCE [Termes IGN] erreur systématique [Termes IGN] géoïde gravimétrique [Termes IGN] géoïde terrestre [Termes IGN] harmonique sphérique [Termes IGN] hauteur ellipsoïdale [Termes IGN] modèle de géopotentiel [Termes IGN] problème des valeurs limites [Termes IGN] résidu [Termes IGN] système de référence altimétrique Résumé : (Auteur) One of the main objectives of ESA’s Gravity Field and Steady-State Ocean Circulation mission GOCE (Gravity field and steady-state ocean circulation mission, 1999) is to allow global unification of height systems by directly providing potential differences between benchmarks in different height datum zones. In other words, GOCE provides a globally consistent and unbiased geoid. If this information is combined with ellipsoidal (derived from geodetic space techniques) and physical heights (derived from leveling/gravimetry) at the same benchmarks, datum offsets between the datum zones can be determined and all zones unified. The expected accuracy of GOCE is around 2–3 cm up to spherical harmonic degree nmax ~ 200. The omission error above this degree amounts to about 30 cm which cannot be neglected. Therefore, terrestrial residual gravity anomalies are necessary to evaluate the medium and short wavelengths of the geoid, i.e. one has to solve the Geodetic Boundary Value Problem (GBVP). The theory of height unification by the GBVP approach is well developed, see e.g. Colombo (A World Vertical Network. Report 296, Department of Geodetic Science and Surveying, 1980) or Rummel and Teunissen (Bull Geod 62:477–498, 1988). Thereby, it must be considered that terrestrial gravity anomalies referring to different datum zones are biased due to the respective datum offsets. Consequently, the height reference surface of a specific datum zone deviates from the unbiased geoid not only due to its own datum offset (direct bias term) but is also indirectly affected by the integration of biased gravity anomalies. The latter effect is called the indirect bias term and it considerably complicates the adjustment model for global height unification. If no satellite based gravity model is employed, this error amounts to about the same size as the datum offsets, i.e. 1–2 m globally. We show that this value decreases if a satellite-only gravity model is used. Specifically for GOCE with nmax ~ 200, the error can be expected not to exceed the level of 1 cm, allowing the effect to be neglected in practical height unification. The results are supported by recent findings by Gatti et al. (J Geod, 2012). Numéro de notice : A2013-074 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-012-0579-y En ligne : https://doi.org/10.1007/s00190-012-0579-y Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=32212 [article]

Exemplaires(1)

Code-barres	Cote	Support	Localisation	Section	Disponibilité
266-2013011	SL	Revue	Centre de documentation	Revues en salle	Disponible