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1998 Analysis center workshop proceedings, Darmstadt, February 9-11, 1998 / J.M. Dow (1998)

Titre : 1998 Analysis center workshop proceedings, Darmstadt, February 9-11, 1998 Type de document : Actes de congrès Auteurs : J.M. Dow, Editeur scientifique ; J. Kouba, Editeur scientifique ; International GPS service for geodynamics, Auteur ; Tim A. Springer, Editeur scientifique Congrès : IGS 1998, Analysis center workshop (9 - 11 février 1998; Darmstadt, Allemagne), Auteur Editeur : Paris : Agence Spatiale Européenne ASE / European Space Agency ESA Année de publication : 1998 Importance : 400 p. Format : 21 x 30 cm Note générale : Bibliographie Langues : Anglais ( eng)Descripteur : [Vedettes matières IGN] Géodésie spatiale

[Termes descripteurs IGN] Global Orbitography Navigation Satellite System

[Termes descripteurs IGN] International Terrestrial Reference Frame

[Termes descripteurs IGN] orbitographie par GNSS

[Termes descripteurs IGN] propagation ionosphérique

[Termes descripteurs IGN] propagation troposphériqueNote de contenu : Foreword / JM Dow

Programme of Workshop

List of Participants

Executive Summary / G. Beutler

Summary Recommendations of the Darmstadt Workshop

Recommendation and Action Items of the IGS Governing Board Retreat, Napa Valley, December 12-14 1997 / /./. Mueller

Topic 1: The IGS Analysis Products and Consistency of the Combination Solutions

The IGS analysis products and the consistency of the combined solutions / T. Springer, J. Zumberge, J. Kouba

Efficient estimation of precise high-rate GPS clocks (Abstract only) /J. Zumberge, F. Webb, M, Watkins

Precise high-rate satellite clocks at GFZ / W. Sohne

The IGS/BIPM time transfer project / J.Ray

Topic 2: Orbit Prediction and Rapid Products

Orbit predictions and rapid products / T. Martin-Mur, T. Springer, Y. Bar-Sever

A new solar radiation pressure model for the GPS satellites / T. Springer, G. Beutler, M. Rothacher

New solar radiation pressure models for GPS satellites (Abstract only) / Y. Bar-Sever, D. Jefferson, L. Romans

A look at the IGS predicted orbit (Abstract only) /J. Zumberge

Real time ephemeris and clock corrections for GPS and GLONASS Satellites / M. Romay-Merino, J. Nieto-Recio, J. Cosmen-Shortmann, J. Martin-Piedelobo

Potential use of orbit predictions and rapid products in the GRAS programme / P. Silvestrin

Topic 3: IGS Reference Frame Realisation and Contributions to ITRF

IGS reference frame realization / J. Kouba, J. Ray, M. Watkins

ITRF96 and follow-on for 1998 / C Boucher, Z. Altamimi, P. Sillard

IGS reference stations classification based on ITRF96 residual analysis / Z. Altamimi

Estimation of nutation terms using GPS / M. Rothacher, G. Beutler

Globally consistent rigid plate motion: Fiducial-free Euler vector estimation / G. Blewitt, R. Kawar, and P. Davies

Topic 4: IGS Products for Troposhpere and Ionosphere

IGS Combination of tropospheric estimates - experience from pilot experiment / G. Gendt

Water vapour from observations of the German Geodetic GPS reference network (GREF) (Summary) / M Becker, G. Weber, C. Kopken

Estimating horizontal gradients of tropospheric path delay with a single GPS receiver (Abstract only) / Y. Bar-Sever, P. Kroger, J. Borjesson

IGS products for the ionosphere / J. Feltens, S. Schaer

IONEX: The lONosphere Map EXchange, Format Version 1 / S. Schaer, W. Gurtner, J. Feltens

The study of the TEC and its irregularities using a regional network of GPS stations / R. Warnant

Monitoring the ionosphere over Europe and related ionospheric studies / N. Jakowski, S. Schluter, A. Jungstand

Routine production of ionospheric TEC maps at ESOC - first results / J. Feltens, J. Dow, T. Martin~Mur, C. Garcia-Martinez, P. Bernedo

Chapman profile approach for 3-D global TEC representation / J. Feltens

The role of GPS data in ionospheric monitoring, mapping and nowcasting / R. Leitinger

Mapping and predicting the ionosphere / S. Schaer, G. Beutler, M. Rothacher

Contributed papers on other topics

Experiences of the BKG in processing GLONASS and combined GLONASS/GPS observations / H. Habrich

Precise autonomous ephemeris determination for future navigation satellites / M. Romay-Merino, P. van Niftrik

ARP project: Absolute and relative orbits using GPS / T. Martin-Mur, C. Garcia-Martinez

Poster Summary Papers

IGS related activities at the Geodetic Survey Division of Natural Resources Canada / C. Huot, P Tetreault, Y. Mireault, P. Heroux, R. Ferland, D. Hutchison and J. Kouba

ESA/ESOC IGS Analysis Centre poster summary / C. Garcia-Martinez, J. Dow, T. Martin-Mur, J. Feltens, P. Bernedo

Recent IGS Analysis Center Activities at JPL / D. Jefferson, Y. Bar-Sever, M. Heflin, M. Watkins, F. Webb, J. Zumberge

A review of GPS related activities at the National Geodetic Survey / M. Schenewerk, S. Mussman, G. Mader and E. Dutton

U.S. Naval Observatory: Center for rapid service and predictions / J. Ray, J. Rohde, P. Kammeyer and B. Luzum

The IGS Regional Network Associate Analysis Center for South America at DGFL / W. Seemuller, H. Drewes

The Newcastle Global Network Associate Analysis Centre / R. Kawar, G. Blewitt and P. DaviesNuméro de notice : 14475 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Actes Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=34664 ## Réservation

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Code-barres Cote Support Localisation Section Disponibilité 14475-01 CG.98 Livre Centre de documentation Congrès DisponibleOcean tides and tectonic plate motions from LAGEOS / J.M. Dow (1988)

Titre : Ocean tides and tectonic plate motions from LAGEOS Type de document : Thèse/HDR Auteurs : J.M. Dow, Auteur Editeur : Munich : Bayerische Akademie der Wissenschaften Année de publication : 1988 Collection : DGK - C Sous-collection : Dissertationen num. 344 Importance : 180 p. Format : 21 x 30 cm ISBN/ISSN/EAN : 978-3-7696-9392-8 Langues : Anglais ( eng)Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale

[Termes descripteurs IGN] analyse harmonique

[Termes descripteurs IGN] application informatique

[Termes descripteurs IGN] données TLS (télémétrie)

[Termes descripteurs IGN] Lageos

[Termes descripteurs IGN] marée océanique

[Termes descripteurs IGN] marée terrestre

[Termes descripteurs IGN] orbite circulaire

[Termes descripteurs IGN] orbitographie

[Termes descripteurs IGN] perturbation orbitale

[Termes descripteurs IGN] rotation de la Terre

[Termes descripteurs IGN] tectonique des plaquesRésumé : (Auteur) The objectives of this study were twofold:

to provide a detailed and systematic analysis of the influence of solid earth, ocean and atmospheric tides on the orbits of earth satellites; and

to apply the insight thus obtained in order to contribute to high precision determination of such orbits from ground tracking data, a process which requires simultaneous improvement of a number of geophysical models which are of interest in themselves.

A review of the relevant theoretical background concerning the mathematical description of the tide-generating potential and the response of the solid earth, oceans and atmosphere to this potential has been made, with a strong emphasis on several remarkable modern advances in this field, culminating in the work of Wahr in earth tides and that of Schwiderski in global ocean tide modelling.

The formulation of the tide-generating potential by Cartwright and Taylor (1972) has been used as the starting point for the development of a theory for the motion about an oblate earth of a satellite perturbed by the tidal response of the solid earth. Taking advantage of a well-known transformation procedure due to Kaula (1966), the perturbing potential could be written as a function of the keplerian elements of the satellite, and with this the Lagrange planetary equations provided the first order perturbations on the elements. Important second order perturbations arising from the coupling between the tidal perturbations and those secular perturbations due to the permanent oblateness of the earth were derived.

The principal and secondary frequencies of the resulting perturbations have been classified, showing clearly the dependence on the astronomical driving frequency and on the frequencies associated with the secular rates of the satellite angular elements. It has been shown that for certain critical combinations of these frequencies, which can arise for real satellite orbits of interest, the resulting perturbation frequency can be zero, so that the elements have secular variations. Unlike the secular variations coming from the oblateness perturbation, these apply also to the orbital inclination. The cumulative effect is however of such a magnitude, even over a typical satellite mission duration, that the linearity assumptions remain valid.

This approach differs from that of Kaula (1969), and of Lambeck (1980) and previous publications of Lambeck, Cazenave and Balmino (1974) and Cazenave, Daillet and Lambeck (1977), through the use of the Cartwright form of the tide-generating potential. This implicitly contains the lunar and solar motions in terms of their ecliptic, rather than equatorial elements, and thus gives a precisely correct representation of the relevant astronomical frequencies, and avoids any ambiguity in the application of frequency-dependent Love numbers. Musen and co-workers (1972, 1973, 1975) have also derived a theory in terms of ecliptic elements.

An analogous development has been carried out for ocean (and atmospheric) tidal perturbations on satellite motion. Here the starting point is a set of existing global ocean tide models obtained from integration of a generalised version of the Laplace tidal equations (Schwiderski). The external potential of a thin mass layer distributed over the surface of the earth is required, assuming a spherical harmonic representation of the mass layer and taking into account the additional potential due to loading of the underlying solid earth. Again, the Lagrange planetary equations were used to obtain the first order and most important second order perturbations on the elements. The approach adopted for the ocean tide developments is similar to that of Lambeck et al. (1974) and Lambeck (1980), but it is complete for all 6 elements and removes several errors in Lambeck's formulation.

The frequency spectrum for ocean tide perturbations is considerably more diverse than that of the solid earth perturbations due to the relative importance of harmonics of degree > 2. Pairs of frequencies appear, corresponding to positive and negative contributions of the astronomical frequency to the total perturbation frequency ('prograde' and 'retrograde' waves). It was shown that in general only the prograde terms can produce long-periodic perturbations, though there can be exceptions to this in cases of near-resonance.

In order to provide a consistent and complete set of spherical harmonic coefficients for a numerical study of the tidal perturbations, a spherical harmonic analysis of the 11 Schwiderski tidal models was performed, using a specially developed FORTRAN program ('KUGEL'). The 1 ° by 1 ° data for the amplitude multiplied by sine and cosine respectively of the phase were approximated up to degree and order 36, giving both prograde and retrograde coefficient sets. Since global synthesis of the spherical harmonics showed a surprising (rms and maximum) discrepancy with respect to the original data, a detailed investigation of the source of the inaccuracy was made. It was found that the agreement was everywhere good except around the coastlines. Significant zero degree coefficients reflect the non-conservation of water mass in the Schwiderski models. The extremely local coastal errors could only be removed by very high degree and order approximation, and are of no relevance for orbit perturbation analysis, except for very low orbits ( < 150 km).

The theory and numerical data thus obtained were implemented in a new FORTRAN program TIDES' aimed at generating a complete overview of the tidal perturbations on earth satellite orbits. The full second and third degree tide-generating potential was used in computing earth tide perturbations, while the ocean tide spectrum was represented by the 11 major tides for which models currently exist. Both prograde and retrograde terms were included in the latter. The S2 atmospheric tide was treated by analogy with the ocean tide. Emphasis was given to development of a concise graphical representation of the perturbation amplitudes, taking into account the fact that a given spectral line may arise from several tides and from the solid earth, ocean or atmospheric response, necessitating the combination of contributions having arbitrary phases.

A detailed application of this software was made to the orbits of Lageos, ERS-1, Starlette, GRM, GPS, EURECA, TOPEX and a geostationary satellite. The analysis of the Lageos orbit was used as the basis for the selection of tidal parameters to be determined in the second part of the study. It was shown that the sun-synchronism of ERS-1 is responsible for the existence of secular perturbations associated with the S2 tide, with rates in the angular elements of 1.9 m/d in the inclination and -5.8 m/d in the mean argument of latitude. Sun-synchronism causes degeneracy of the spectrum, including a concentration of lines around periods of 6 months and 1 y. Retrograde terms affect the orbit at the cm level. Third degree earth tides produce small perturbations on the eccentricity vector with monthly and ter-monthly periods. The frozen perigee produces a further degeneration of the spectrum of tidal perturbations on ERS-1. The Starlette, EURECA and

TOPEX orbital parameters produce a very rich tidal spectrum, due in part to significant values of both nodal and perigee rotation rates, with a concentration of lines at relatively high frequencies. The main long-period perturbations are from AT,, /*,, S2, Kt and A/2. The 5a atmospheric tide affects the TOPEX orbit by 2 m. GRM has resonances from the declination tides AT, and K2, due to the zero nodal rotation rate associated with a polar orbit about an oblate planet. The tides generate perturbation rates of several m/d on the node. The GPS satellites, in 12 hr orbits, exhibit a remarkable concentration of the tidal spectrum at very low frequencies (periods > 2300 d), and otherwise some semi-annual perturbations. A systematic analysis of this type has not appeared in the published literature.

The second part of this work involved the processing of a large data set of 3.3 y of laser ranging data from Lageos with a view to determining improved values for a sub-set of the ocean tide parameters affecting the motion of Lageos. An essential by-product in this was the precise determination of a large number of other parameters entering the mathematical models of the spacecraft motion and the laser ranging data: orbital elements, radiation pressure and empirical drag parameters, low degree and order gravity coefficients, the gravitational constant for the earth GM,, station positions and tectonic motions, second degree Love and Shida numbers defining tidal uplift and horizontal motion, and polar motion.

A previously developed orbit determination program ('BAHN') was modified to handle estimation of tidal and gravity parameters. An algorithm for combination of arbitrary sets of normal equations created by individual runs of the orbit determination software was implemented in a program called 'MULTIARC', which allows a partitioning of the normal equations according to a sub-division of the state variables to be estimated into arc-dependent and arc-independent classes.

Due to the very long overall length of the data span being processed, it was considered necessary to model the tectonic plate motions of the tracking stations. An option of estimating station velocities in the local topocentric coordinate system (east, north, up) was implemented in BAHN. As a first approximation, any existing tectonic plate model (e.g. that of Minster and Jordan) can be used. Software modules were also written to compare global station coordinate solutions (via a 7 parameter transformation) and to compare two series of earth rotation parameters (pole, UT1, LOD).

Three trial solutions were made by processing the 14 month MERIT data set (September 1983 to October 1984): first, in order to check the multi-arc approach, by generating a new station coordinate set from the combination of monthly arcs; second, as a test of the estimation of tidal parameters; and finally as a check on the effect of modelling plate motions. The first solution (TS1) showed an rms agreement over 20 stations of about 2 cm with a MERIT station coordinate solution previously obtained by the University of Texas. The second indicated a reasonable recovery of second degree parameters for the A/2, 52 and N2 tides, and a notable reduction in the rms laser residuals, suggesting that a significant signal had been removed from the data. The third test incorporated station velocities in a multi-arc solution for the network, using the Minster and Jordan AMO-2 model.

The final step was the derivation of a multi-year solution (TS4) for 60 tidal parameters by reduction of data from 40 arcs, each of 30 d duration, spanning the period September 1983 to December 1986, a total of nearly 170000 measurements. Initial estimates of the orbital elements and new stations appearing in the post-MERIT data had first to be derived. A set of 60 tidal parameters from 20 tides was selected on the basis of the Lageos perturbation analysis.

The solution is summarised as follows:

The along-track acceleration parameter showed a clear correlation with eclipse periods, in the sense of alternate minima and maxima during successive eclipse seasons, while maintaining a constant mean level of around -3 x 10~13 m/s2.

The pole coordinates were determined with 3 d resolution. In order to clearly separate earth rotation from tidal signals on the orbit node, UT1 was held fixed at the values obtained by interpolation in the 5 d VLBI solution ERP(NGS) 87 R 01. The two pole series show an rms discrepancy of 2.29 masec in xp and 2.16 masec in yf, with mean linear trends over 40 months of 1.65 x 10~3 and 0.37 x 10~3 masec/d. A small residual signal, mainly annual, remains, despite the fact that the small solar annual Sa tide was adjusted. Estimation of tidal parameters did however improve the agreement.

For 14 stations, reliable estimates of not only station positions but also secular (tectonic) velocities could be derived. Previous approaches to determining station motions from laser tracking have relied on deducing velocity a posteriori from successive determinations of position. The new technique employed here allowed the station velocities to be estimated directly from the whole data set. Agreement with a University of Texas solution SSC(CSR) 86 L 01 which used Minster and Jordan AM 1-2 plate motions was at the level of < 2 cm rms for epochs before 1986.0, but somewhat worse in longitude thereafter. (Time-varying 7-parameter transformation parameters were generated in the comparison.) The terrestrial reference frame was defined by holding fixed the longitude and longitude rate of one station (Matera), and the latitude and latitude rate of two stations (Matera and Arequipa). It was shown that the choice of stations here was not important, though they must be well separated. A network of baseline distances and rates was computed and the latter compared with those predicted by the Minster and Jordan (1978) model. In most cases the agreement was good (very small rates in intra-plate baselines, rates between North American and European stations ~ 15 mm/y) but there were a few notable exceptions. The Southern Californian station Monument Peak was shown to have a significant relative motion with respect to other laser stations on the North American plate: its motion is more consistent with a location on the neighbouring Pacific plate. The baseline Monument Peak - Quincy which lies along the San Andreas fault line was estimated to have a rate of -39 mm/y, in close agreement with the value of -35 mm/y derived by Clark et al. (1987) from VLBI measurements. No significant relative motion was detected along the line Quincy - Mazatlan (Mexico), which also roughly follows the San Andreas fault direction: both points are well outside the geologically unstable region assocated with the fault. A small contraction (~ 10 - 20 mm/y) was detected in baselines between North and South America (Arequipa) and between South America and Europe. Tectonic plate models (Chase 1978, Minster and Jordan 1978) do not constrain these motions very well, so that their predictions are more uncertain. The real (as opposed to formal) uncertainty of the laser baseline rate solutions is estimated to be about 10 mm/y for these lines. Although motions between Hawaii and the North American, Indian (Australia) and Eurasian plates are fairly consistent with the Minster-Jordan predictions, the south Pacific island station of Huahine exhibits significant additional westerly and northerly motions with respect to the prediction. Comparison with information from other techniques will be required in order to confirm whether or not this motion is real.

Since the modified GEM-L2 gravity model which was used in this work was computed without any consideration of ocean tides, 10 low degree and order gravity coefficients were included in the TS4 solution. The shifts were in all cases small, ranging from 1 part in 107 in C20 to 1%

in 5"4,. The C21 and S2l coefficients were estimated in order to take into account a small offset between the terrestrial reference pole and the mean axis of figure . A recent analysis of Wahr (1987) was applied to compute from these values a tentative estimate for the relative equatorial rotation rate of the core with respect to the mantle. Both components are of the order of 1(H times the rotation rate of the mantle.

A new value for the earth's gravitational constant GM, was determined: GM, = 398600.4406 ± 0.0002 (formal error). This value is consistent with the MERIT value of 398600.448 km3/s2, which was used as initial estimate, but while the latter is applicable to the solar system barycentric frame, the new value is recommended for computation of earth satellite orbits.

The Love number hj and Shida number 4 which provide a measure of vertical and horizontal tidal displacements at the earth's surface were estimated to be fij = 0.639, /2 = 0.113. The differences with respect to the values of Wahr (1981b) are equivalent to displacement amplitudes of ~ 1 cm, and can be partially explained by the neglect of ocean loading in computing station positions in the TS4 solution.

Improved coefficients were determined for the spherical harmonic development of 4 long-period tides (Sa, Ssa, Mm, Mf), 6 diurnal tides (Q{, Ot, /*,, A",, 165.575, ^,), and 6 semi-diurnal tides (N2, A/2, T» S2, K2, 275.575). In all cases 2nd degree coefficients were estimated; in addition, 3rd and in three cases 4th, degree coefficients were computed where the analysis of the perturbation amplitudes had indicated a significant contribution from these. The excellent observability apparent from the covariance propagation in the solution suggested that a considerably larger set of coefficients could be determined from the 1200 d data span. Comparison with the equivalent Schwiderski model (where available) indicated differences in phase which were in most cases less than 15° , but differences in amplitude of more than 30% in a few cases. Comparison with a very recently published solution from Goddard Space Flight Center, based on data from 17 satellites and including parameter estimates for 11 tides (Marsh et al. 1987), showed in general a high level of agreement. In particular, the 2nd degree amplitude and phase for A/2 are almost identical (3.27/3.26 cm, 322.1/320.9°) but significantly different from the Schwiderski values (2.96 cm, 310.6° ). This term is important in quantifying the energy dissipation in the earth-moon system. For the small Sa tide, for which no Schwiderski model exists, similar estimates were obtained (2.37/2.44 cm, 40.5/31.0°).

Simultaneous determination of ocean tide and tectonic plate parameters has not been reported in the literature. It was shown that estimation of each of these two classes of parameters is not excessively sensitive to the other, but non-negligible cross-coupling does occur.

By reprocessing a representative sample of the 30 d arcs (every fourth arc) with the new solution, it was found that the mean of the rms laser residuals in a monthly arc was reduced from 10.45 cm (TS1) to 7.06 cm (TS4), clearly demonstrating that a significant signal had been removed from the data by physically meaningful estimation of key model parameters.Numéro de notice : 58685 Affiliation des auteurs : non IGN Thématique : POSITIONNEMENT Nature : Thèse étrangère Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=60417 ## Réservation

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Code-barres Cote Support Localisation Section Disponibilité 58685-01 30.83 Livre Centre de documentation Géodésie Disponible