Why the 18.6 year tide cannot explain the change of sign observed in &amp;lt;i&amp;gt;j&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;&amp;lt;/i&amp;gt;

Deleflie, F.; Exertier, P.; Métris, Gilles; Bério, Philippe; Laurain, O.; Lemoine, Jean‐Michel; Biancale, R.

doi:10.5194/adgeo-1-103-2003

Cited by 9 publications

(4 citation statements)

References 11 publications

(9 reference statements)

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“…It allows us to simultaneously determine both precise averaged satellite orbits and geophysical parameters over periods of 20 years and more [17]. Thus, the early SLR data are still important in the separation of effects with long characteristic time scales, such as post-glacial rebound and 18.6-yr tide [14]. Currently, data spanning 28 years from six to eight satellites are used for measuring the large-scale mass movements on the Earth [11].…”

Section: Earth Gravity Fieldmentioning

confidence: 99%

Contribution of laser ranging to Earth's sciences

Exertier

Bonnefond

Deleflie

et al. 2006

Comptes Rendus. Géoscience

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Satellite and Lunar Laser Ranging (SLR and LLR, respectively) are based on a direct measurement of a distance by exactly measuring the time transit of a laser beam between a station and a space target. These techniques have proven to be very efficient methods for contributing to the tracking of both artificial satellites and the Moon, and for determining accurately their orbit and the associated geodynamical parameters, although hampered by the non-worldwide coverage and the meteorological conditions. Since more than 40 years, the French community (today 'Observatoire de la Côte d'Azur', CNES, 'Observatoire de Paris', and IGN) is largely involved in the technological developments as well as in the scientific achievements. The role of the laser technique has greatly evolved thanks to the success of GPS and DORIS; the laser technique teams have learnt to focus their effort in fields where this technique is totally specific and irreplaceable.The role of SLR data in the determination of terrestrial reference systems and in the modelling of the first terms of the gravity field (including the terrestrial constant GM that defines the scale of orbits) has to be emphasized, which is of primary importance in orbitography, whatever the tracking technique used. In addition, the role of LLR data (with two main stations, at Mac Donald (United States) and Grasse (France), since 30 years) has been of particular importance for improving solar system ephemeris and contributing to some features of fundamental physics (equivalence principle). Today, the role of the SLR technique is (i) to determine and to maintain the scale factor of the global terrestrial reference frame, (ii) to strengthen the vertical component (including velocity) of the positioning, which is crucial for altimetry missions and tectonic motions, (iii) to locate the geocenter with respect to the Earth's crust, (iv) to avoid any secular and undesirable drift of geodetic systems thanks to a very good accuracy. Now, the future of this technique is to enlarge the technical capability of laser ranging stations for long distances, that is the tracking of space targets orbiting through the Solar System. In addition, the laser technique should participate into time transfer experiments and improve, with mobile systems like the FTLRS and the new SLR2000 concept, the coverage of the international laser network (ILRS).

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Section: Earth Gravity Fieldmentioning

confidence: 99%

Contribution of laser ranging to Earth's sciences

Exertier

Bonnefond

Deleflie

et al. 2006

Comptes Rendus. Géoscience

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“…Cox and Chao (2002) published a very interesting work on an anomalous behavior of Earth's _ J 2 . They found, from an accurate analysis of 25 years of SLR observations from various satellites, including data from the two LAGEOS's, the observational evidence that J 2 started increasing around 1998, at least for a few years (see also Cheng and Tapley, 2004a,b;Deleflie et al, 2003).…”

Section: The Even Zonal Harmonics Secular Variations: First Partmentioning

confidence: 95%

The LAGEOS satellites orbital residuals determination and the way to extract gravitational and non-gravitational unmodeled perturbing effects

Lucchesi

2007

Advances in Space Research

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“…h This anomalous mass re-distribution is still unexplained from the geophysical point of view. 32 There is no more to say in order to explain the importance of the secular trends in the firsts even zonal harmonics coefficients.…”

Section: The Impact Of the Secular Variations Of The Even Zonal Harmomentioning

confidence: 99%

The Impact of the Even Zonal Harmonics Secular Variations on the Lense–thirring Effect Measurement With the Two Lageos Satellites

Lucchesi

2005

Int. J. Mod. Phys. D

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This work has been motivated by the criticisms raised on the error budget contributionon a recently performed measurement of the Lense-Thirring effect -from the uncertainties of the secular variations of the Earth's even zonal harmonics. The relativistic secular precession has been observed from the analysis of 11 years of LAGEOS and LAGEOS II laser ranging data. In the analysis, the recent EIGEN-GRACE02S gravity field model (derived from GRACE data only) was used during the orbit determination process using the NASA Goddard software package GEODYN II. In particular, the measurement has been derived combining the nodes only of the two LAGEOS satellites in order to cancel the larger error source, due to the uncertainty of the first even zonal harmonic, and solved for the Lense-Thirring effect predicted by Einstein's general relativity. The authors of the relativistic measurement claimed an error of about 1% of the relativistic effect as due to the temporal variation of the even zonal harmonics. The main criticism is that on a much larger error estimate, about 11% of the relativistic effect on the analyzed time span of the two LAGEOS satellites orbital data should be considered. Moreover, the authors of the relativistic measurement emphasized that whatever the value they chose for the secular variations, in particular of the effective value forJ 4 , they always obtained the same discrepancy of about 1% between the observed and predicted effect, without however providing a detailed explanation. In the present work we address all the cited aspects. In particular, we explain the physical reason for the results obtained by the authors of the relativistic measurement in all their simulations. As we will see, two additional errors (linear in time) must be considered in the satellites orbit analysis if we want to correctly explain the experimental results. The first is a time-dependent error related with the mismodeling of the secular variations of the even zonal harmonics. The inclusion of this error in the error analysis explains why the same discrepancy between the observed and predicted effect has been always obtained independently of the assumed value forJ eff 4 , i.e. for the errors in the time variations of the even zonal harmonics. 1989 Int. J. Mod. Phys. D 2005.14:1989-2023. Downloaded from www.worldscientific.com by CAMBRIDGE UNIVERSITY on 02/03/15. For personal use only. 1990 D. M. LucchesiThe second is a time-independent error related to the non-coincidence between the reference epoch of the gravity field, i.e. the middle epoch of the time span during which the gravity field has been determined by the GRACE mission, and the reference epoch fixed in the orbit analysis program. The inclusion of this error in the error analysis explains the 1% value for the discrepancy between the prediction and the observations. In order to validate our results we fitted for an effectiveJ eff 4 from the combined nodes of the LAGEOS satellites with the EIGEN2S gravity field model obtained from the CHAMP mission. From our fit, we ...

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Why the 18.6 year tide cannot explain the change of sign observed in <i>j<sub>2</sub></i>

Cited by 9 publications

References 11 publications

Contribution of laser ranging to Earth's sciences

Contribution of laser ranging to Earth's sciences

The LAGEOS satellites orbital residuals determination and the way to extract gravitational and non-gravitational unmodeled perturbing effects

The Impact of the Even Zonal Harmonics Secular Variations on the Lense–thirring Effect Measurement With the Two Lageos Satellites

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