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Anomalous harmonics in the spectra of GPS position estimates / Jim Ray in GPS solutions, vol 12 n° 1 (January 20008)
[article]
Titre : Anomalous harmonics in the spectra of GPS position estimates Type de document : Article/Communication Auteurs : Jim Ray, Auteur ; Zuheir Altamimi , Auteur ; Xavier Collilieux , Auteur ; Tonie M. van Dam, Auteur Année de publication : 2008 Article en page(s) : pp 55 – 64 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale
[Termes IGN] coordonnées GPS
[Termes IGN] erreur systématique
[Termes IGN] série temporelleRésumé : (auteur) Prior studies of the power spectra of GPS position time series have found pervasive seasonal signals against a power-law background of flicker noise plus white noise. Dong et al. (2002) estimated that less than half the observed GPS seasonal power can be explained by redistributions of geophysical fluid mass loads. Much of the residual variation is probably caused by unidentified GPS technique errors and analysis artifacts. Among possible mechanisms, Penna and Stewart (2003) have shown how unmodeled analysis errors at tidal frequencies (near 12- and 24-hour periods) can be aliased to longer periods very efficiently. Signals near fortnightly, semiannual, and annual periods are expected to be most seriously affected. We have examined spectra for the 167 sites of the International GNSS (Global Navigation Satellite Systems) Service (IGS) network having more than 200 weekly measurements during 1996.0–2006.0. The non-linear residuals of the weekly IGS solutions that were included in ITRF2005, the latest version of the International Terrestrial Reference Frame (ITRF), have been used. To improve the detection of common-mode signals, the normalized spectra of all sites have been stacked, then boxcar smoothed for each local north (N), east (E), and height (H) component. The stacked, smoothed spectra are very similar for all three components. Peaks are evident at harmonics of about 1 cycle per year (cpy) up to at least 6 cpy, but the peaks are not all at strictly 1.0 cpy intervals. Based on the 6th harmonic of the N spectrum, which is among the sharpest and largest, and assuming a linear overtone model, then a common fundamental of 1.040 ± 0.008 cpy can explain all peaks well, together with the expected annual and semiannual signals. A flicker noise power-law continuum describes the background spectrum down to periods of a few months, after which the residuals become whiter. Similar sub-seasonal tones are not apparent in the residuals of available satellite laser ranging (SLR) and very long baseline interferometry (VLBI) sites, which are both an order of magnitude less numerous and dominated by white noise. There is weak evidence for a few isolated peaks near 1 cpy harmonics in the spectra of geophysical loadings, but these are much noisier than for GPS positions. Alternative explanations related to the GPS technique are suggested by the close coincidence of the period of the 1.040 cpy frequency, about 351.2 days, to the “GPS year”; i.e., the interval required for the constellation to repeat its inertial orientation with respect to the sun. This could indicate that the harmonics are a type of systematic error related to the satellite orbits. Mechanisms could involve orbit modeling defects or aliasing of site-dependent positioning biases modulated by the varying satellite geometry. Numéro de notice : A2008-568 Affiliation des auteurs : LAREG+Ext (1991-2011) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s10291-007-0067-7 Date de publication en ligne : 15/05/2007 En ligne : https://doi.org/10.1007/s10291-007-0067-7 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=103421
in GPS solutions > vol 12 n° 1 (January 20008) . - pp 55 – 64[article]Comparison of very long baseline interferometry, GPS, and satellite laser ranging height residuals from ITRF2005 using spectral and correlation methods / Xavier Collilieux in Journal of geophysical research : Solid Earth, vol 112 n° B12 (December 2007)
[article]
Titre : Comparison of very long baseline interferometry, GPS, and satellite laser ranging height residuals from ITRF2005 using spectral and correlation methods Type de document : Article/Communication Auteurs : Xavier Collilieux , Auteur ; Zuheir Altamimi , Auteur ; David Coulot , Auteur ; Jim Ray, Auteur ; Patrick Sillard , Auteur Année de publication : 2007 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale
[Termes IGN] analyse comparative
[Termes IGN] corrélation
[Termes IGN] données GPS
[Termes IGN] données ITGB
[Termes IGN] données TLS (télémétrie)
[Termes IGN] résiduRésumé : (auteur) For the first time, the ITRF2005 input data are in the form of time series of station positions and Earth orientation parameters, together with full variance-covariance information. The first step of the ITRF2005 analysis consists of rigorously stacking each time series to yield a long-term solution per technique. As a by-product, time series of position residuals contain the nonlinear motion of points over the Earth's surface. In this paper, the height residual time series of very long baseline interferometry (VLBI), Global Positioning System (GPS), and satellite laser ranging (SLR) solutions submitted to ITRF2005 are compared. We note that the interpretation of the ITRF2005 position residual time series as observed physical motions at the various stations is delicate due to the inhomogeneous site distribution. We estimate that the network effect may introduce an averaged scatter of 3 and 2 mm in the VLBI and SLR height residuals, respectively. Although noise levels are different among these three techniques, a common 1.0 cycles per year (cpy) frequency is clearly detected. The GPS height annual signal exhibits significant regional correlations that are confirmed by VLBI and SLR measurements in some colocated sites. Significant power near frequencies 2.00, 3.12, and 4.16 cpy is also detected in the individual GPS height residuals time series as mentioned by Ray et al. (2007). However, neither VLBI nor SLR show any significant signals at these frequencies for colocated sites. The agreement between detrended height time series at colocated sites is quantified using a novel method based on Kalman filtering and on maximum likelihood estimation. The GPS and VLBI measurements are shown to agree fairly well for most of the colocated sites. However, agreement is not generally observed in the GPS and SLR comparisons. A study of the interannual signal at colocated sites indicates that the good correlation cannot be completely attributed to the annual harmonic. Numéro de notice : A2007-660 Affiliation des auteurs : LAREG+Ext (1991-2011) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1029/2007JB004933 Date de publication en ligne : 28/12/2007 En ligne : https://doi.org/10.1029/2007JB004933 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=102705
in Journal of geophysical research : Solid Earth > vol 112 n° B12 (December 2007)[article]Is there utility in rigorous combinations of VLBI and GPS Earth orientation parameters? / Jim Ray in Journal of geodesy, vol 79 n° 9 (December 2005)
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Titre : Is there utility in rigorous combinations of VLBI and GPS Earth orientation parameters? Type de document : Article/Communication Auteurs : Jim Ray, Auteur ; Jan Kouba, Auteur ; Zuheir Altamimi , Auteur Année de publication : 2005 Article en page(s) : pp 505 - 511 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Systèmes de référence et réseaux
[Termes IGN] données GPS
[Termes IGN] données ITGB
[Termes IGN] orientation de la Terre
[Termes IGN] point de liaison (géodésie)
[Termes IGN] positionnement par GPS
[Termes IGN] positionnement par ITGB
[Termes IGN] série temporelle
[Termes IGN] système de référence mondialRésumé : (Auteur) Combinations of station coordinates and velocities from independent space-geodetic techniques have long been the standard method to realize robust global terrestrial reference frames (TRFs). In principle, the particular strengths of one observing method can compensate for weaknesses in others if the combination is properly constructed, suitable weights are found, and accurate co-location ties are available. More recently, the methodology has been extended to combine time-series of results at the normal equation level. This allows Earth orientation parameters (EOPs) to be included and aligned in a fully consistent way with the TRF. While the utility of such multi-technique combinations is generally recognized for the reference frame, the benefits for the EOPs are yet to be quantitatively assessed. In this contribution, which is a sequel to a recent paper on co-location ties (Ray and Altamimi in J Geod 79(4–5): 189–195, 2005), we have studied test combinations of very long baseline interferometry (VLBI) and Global Positioning System (GPS) time-series solutions to evaluate the effects on combined EOP measurements compared with geophysical excitations. One expects any effect to be small, considering that GPS dominates the polar motion estimates due to its relatively dense and uniform global network coverage, high precision, continuous daily sampling, and homogeneity, while VLBI alone observes UT1-UTC. Presently, although clearly desirable, we see no practical method to rigorously include the GPS estimates of length-of-day variations due to significant time-varying biases. Nevertheless, our results, which are the first of this type, indicate that more accurate polar motion from GPS contributes to improved UT1-UTC results from VLBI. The situation with combined polar motion is more complex. The VLBI data contribute directly only very slightly, if at all, with an impact that is probably affected by the weakness of the current VLBI networks (small size and sparseness) and the quality of local ties relating the VLBI and GPS frames. Instead, the VLBI polar motion information is used primarily in rotationally aligning the VLBI and GPS frames, thereby reducing the dependence on co-location tie information. Further research is needed to determine an optimal VLBI-GPS combination strategy that yields the highest quality EOP estimates. Improved local ties (including internal systematic effects within the techniques) will be critically important in such an effort. Copyright Springer Numéro de notice : A2005-596 Affiliation des auteurs : IGN (1940-2011) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-005-0007-7 Date de publication en ligne : 10/11/2005 En ligne : http://dx.doi.org/10.1007/s00190-005-0007-7 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=27727
in Journal of geodesy > vol 79 n° 9 (December 2005) . - pp 505 - 511[article]Réservation
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Code-barres Cote Support Localisation Section Disponibilité 266-05091 RAB Revue Centre de documentation En réserve L003 Disponible 266-05092 RAB Revue Centre de documentation En réserve L003 Disponible Evaluation of co-location ties relating the VLBI and GPS reference frames / Jim Ray in Journal of geodesy, vol 79 n° 4-5 (July 2005)
[article]
Titre : Evaluation of co-location ties relating the VLBI and GPS reference frames Type de document : Article/Communication Auteurs : Jim Ray, Auteur ; Zuheir Altamimi , Auteur Année de publication : 2005 Article en page(s) : pp 189 - 195 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Systèmes de référence et réseaux
[Termes IGN] interférométrie à très grande base
[Termes IGN] point de liaison (géodésie)
[Termes IGN] positionnement par GPS
[Termes IGN] positionnement par ITGB
[Termes IGN] série temporelle
[Termes IGN] système de référence mondialRésumé : (Auteur) We have compared the VLBI and GPS terrestrial reference frames, realized using 5 years of time-series observations of station positions and polar motion, with surveyed co-location tie vectors for 25 sites. The goal was to assess the overall quality of the ties and to determine whether a subset of co-location sites might be found with VLBI–GPS ties that are self-consistent within a few millimeters. Our procedure was designed to guard against internal distortion of the two space-geodetic networks and takes advantage of the reduction in tie information needed with the time-series combination method by using the very strong contribution due to co-location of the daily pole of rotation. The general quality of the available ties is somewhat discouraging in that most have residuals, compared to the space-geodetic frames, at the level of 1–2 cm. However, by a careful selection process, we have identified a subset of nine local VLBI–GPS ties that are consistent with each other and with space geodesy to better than 4 mm (RMS) in each component. While certainly promising, it is not possible to confidently assess the reliability of this particular subset without new information to verify the absolute accuracy of at least a few of the highest-quality ties. Particular care must be taken to demonstrate that possible systematic errors within the VLBI and GPS systems have been properly accounted for. A minimum of two (preferably three or four) ties must be measured with accuracies of 1 mm or better in each component, including any potential systematic effects. If this can be done, then the VLBI and GPS frames can be globally aligned to less than 1 mm in each Helmert component using our subset of nine ties. In any case, the X and Y rotations are better determined, to about 0.5 mm, due to the contribution of co-located polar motion. Copyright Springer Numéro de notice : A2005-593 Affiliation des auteurs : IGN (1940-2011) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-005-0456-z Date de publication en ligne : 30/05/2005 En ligne : http://dx.doi.org/10.1007/s00190-005-0456-z Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=27728
in Journal of geodesy > vol 79 n° 4-5 (July 2005) . - pp 189 - 195[article]Réservation
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Code-barres Cote Support Localisation Section Disponibilité 266-05062 RAB Revue Centre de documentation Revues en salle Disponible 266-05061 RAB Revue Centre de documentation Revues en salle Disponible IGS reference frames: status and future improvements / Jim Ray (2004)
contenu dans Celebrating a decade of the International GPS Service, Workshop & Symposium 2004 / Michael Meindl (2004)
Titre : IGS reference frames: status and future improvements Type de document : Article/Communication Auteurs : Jim Ray, Auteur ; D. Dong, Auteur ; Zuheir Altamimi , Auteur Editeur : Berne : Université de Berne Année de publication : 2004 Conférence : IGS 2004, international symposium, Celebrating a decade of the International GPS Service Symposium 01/03/2004 05/03/2004 Berne Suisse Importance : pp 37 - 63 Format : 21 x 30 cm Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Systèmes de référence et réseaux
[Termes IGN] cohérence des données
[Termes IGN] géocentre
[Termes IGN] International Terrestrial Reference Frame
[Termes IGN] poursuite de satellite
[Termes IGN] station de poursuiteRésumé : (Auteur) The hierarchy of reference frames used in the IGS and the procedures and rationale for realizing them are reviewed. The Conventions of the IERS lag developments in the IGS in a number of important respects. Recommendations are offered for changes in the IERS Conventions to recognize geocenter motion (as already implemented by the IGS) and to enforce greater model consistency in order to achieve higher precision for combined reference frame products. Despite large improvements in the internal consistency of IGS product sets, defects remain which should be addressed in future developments. If the IGS is to remain a leader in this area, then a comprehensive, long-range strategy should be formulated and pursued to maintain and enhance the IGS reference frame, as well as to improve its delivery to users. Actions should include the official designation of a high-performance reference tracking network whose stations are expected to meet the highest standards possible. Numéro de notice : C2004-013 Affiliation des auteurs : LAREG+Ext (1991-2011) Thématique : POSITIONNEMENT Nature : Communication nature-HAL : ComAvecCL&ActesPubliésIntl DOI : sans Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=65024 Status of AFREF Project / Jim Ray (2004)PermalinkTests of IGS Reference Frame Stability / Zuheir Altamimi (2004)PermalinkPermalinkPermalinkNew IGS clock products: a global time transfer assessment / Jim Ray in GPS world, vol 13 n° 11 (November 2002)PermalinkPermalinkLes régions de l'Est / A. Blanc (1960)Permalink