GPS measurements of ocean loading and its impact on zenith tropospheric delay estimates: a case study in Brittany, France   总被引：1，自引：0，他引：1  

S. Vey  E. Calais  M. Llubes  N. Florsch  G. Woppelmann  J. Hinderer  M. Amalvict  M. F. Lalancette  B. Simon  F. Duquenne  J. S. Haase 《Journal of Geodesy》2002,76(8):419-427

 The results from a global positioning system (GPS) experiment carried out in Brittany, France, in October 1999, aimed at measuring crustal displacements caused by ocean loading and quantifying their effects on GPS-derived tropospheric delay estimates, are presented. The loading effect in the vertical and horizontal position time series is identified, however with significant disagreement in amplitude compared to ocean loading model predictions. It is shown that these amplitude misfits result from spatial tropospheric heterogeneities not accounted for in the data processing. The effect of ocean loading on GPS-derived zenith total delay (ZTD) estimates is investigated and a scaling factor of 4.4 between ZTD and station height for a 10° elevation cut-off angle is found (i.e. a 4.4-cm station height error would map into a 1-cm ZTD error). Consequently, unmodeled ocean loading effects map into significant errors in ZTD estimates and ocean loading modeling must be properly implemented when estimating ZTD parameters from GPS data for meteorological applications. Ocean loading effects must be known with an accuracy of better than 3 cm in order to meet the accuracy requirements of meteorological and climatological applications of GPS-derived precipitable water vapor. Received: 16 July 2001 / Accepted: 25 April 2002 Acknowledgments. The authors are grateful to H.G. Scherneck for fruitful discussions and for his help with the ocean loading calculations. They thank H. Vedel for making the HIRLAM data available; D. Jerett for helpful discussions; and the city of Rostrenen, the Laboratoire d'Océanographie of Concarneau, and the Institut de Protection et de S?reté Nucléaire (BERSSIN) for their support during the GPS measurement campaign. Reviews by C.K. Shum and two anonymous referees significantly improved this paper. This work was carried out in the framework of the MAGIC project (http://www.acri.fr/magic), funded by the European Commission, Environment and Climate Program (EC Contract ENV4-CT98–0745). Correspondence to: E. Calais, Department of Earth and Atmospheric Sciences, Purdue University, West Lafayette, IN 47907-1397, USA. e-mail: ecalais@purdue.edu Tel. : +1-765-496-2915; Fax:+1-765-496-1210  相似文献   

The excitation of the Chandler wobble     

S. K. Runcorn  G. A. Wilkins  E. Groten  H. Lenhardt  J. Campbell  R. Hide  B. F. Chao  A. Souriau  J. Hinderer  H. Legros  J. -L. Le Mouel  M. Feissel 《Surveys in Geophysics》1987,9(3-4):419-449

The cause- or causes-of the excitation of the Chandler wobble is one of the most intriguing problems in geophysics. As a result of one of the most valuable examples of an international programme, the positions of the pole have been determined since the late 19th century with remarkable accuracy. These data have always been accepted as of great importance in the study of the atmosphere, oceans and solid Earth. Recently, new techniques have greatly improved the accuracy with which the polar motion can be determined. Interpretation of the older data was made much more difficult because of their errors-for example the interesting suggestion that earthquakes were a cause of the excitation (by D. E. Smylie and L. Manshinha) could not be tested because their effects, if any, were lost in the noise. With the great improvement in the data it is now possible to suppose that comparable advances will be made in the theoretical interpretation. A discussion meeting at the Royal Astronomical Society on 8 May, 1987 on this topic was held and the following gives a short survey of this topic, consisting of brief summaries given by the speakers. This review is therefore a collective one which it is hoped will make more widely known these great technical advances and to fundamental interest of the phenomena of thepolar motion.  相似文献   

Noise limitations in the core-mode band of superconducting gravimeter data     

Olivia Jensen  Jacques Hinderer  David J. Crossley 《Physics of the Earth and Planetary Interiors》1995,90(3-4)

In recent years, several claims of detection of weak harmonic signals in the sub-tidal band of frequencies of high-quality gravimeter data have been made. Here, we review our attempts at confirming Smylie's claim of detection of the Slichter mode of inner-core oscillation using the same four data sets he and his colleagues used. We further examine the homogeneous 2 year data sets obtained from the superconducting gravimeters sited in Strasbourg and at Cantley, Quebec. We show that the power spectra of tidal-reduced, pressure and slew-corrected gravity residuals from these data are indistinguishable from a random walk process except in narrow bands dominated by residual earth tides and by harmonics of the diurnal thermal-atmospheric tide. Such a random ‘brown’ residual could result from mechanical instabilities and electronic noise in the instruments themselves, from site-specific tectonic noise, from local hydrological variations and pier instabilities or it could derive from unaccounted for variability in the atmospheric pressure in the vicinity of the instruments. We argue that the homogeneous 2 year data sets show no evidence whatever of Slichter harmonics even though our preprocessing methods reduce ‘apparent noise levels’ in the core-mode band by almost an order magnitude in comparison with the four data sets originally employed by Smylie et al. and, in their first attempted confirmation of his claimed discovery, by Jensen et al.  相似文献   

Shaping the Rwenzoris: balancing uplift,erosion, and glaciation     

Georg Kaufmann  Matthias Hinderer  Douchko Romanov 《International Journal of Earth Sciences》2016,105(6):1761-1778

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Scientific achievements from the first phase (1997–2003) of the Global Geodynamics Project using a worldwide network of superconducting gravimeters     

Jacques Hinderer  David Crossley 《Journal of Geodynamics》2004,38(3-5):237

This paper aims to review the main scientific achievements which were obtained in the first phase (1997–2003) of the Global Geodynamics Project (GGP) consisting of a worldwide network of superconducting gravimeters (SG) of about 20 instruments. We show that the low noise levels reached by these instruments in various frequency bands allow us either to investigate new signals of very small amplitude or to better determine other signals previously seen. We first report new results in the long-period seismic band with special emphasis on the detection of the ₂S₁ normal mode and the splitting of the fundamental spheroidal mode ₂S₀ after the magnitude 8.4 Peru earthquake in 2001. We also discuss briefly the ‘hum’, which consists of a sequence of fundamental normal modes existing between 2 and 7 mHz even in the lack of any seismic excitation, and was first discovered on the Syowa (in Antarctica) instrument in 1998. We will comment on the search for the Slichter mode ₁S₁ of degree 1 which is associated with a translational motion of the inner core inside the liquid core. Atmospheric effects are reviewed from the local to the global scale and the improvement due to pressure loading computations on residual gravity signals is shown. An interesting study exhibiting the gravity consequence due to sudden rainfall and vertical mass motion in the atmosphere (without ground pressure change) is presented. The precision of the SGs leads to some convincing results in the tidal domain, concerning the fluid core resonance effect (free core nutation (FCN)) on diurnal tides or various loading effects (linear, non-linear) from the oceans. In particular, SGs gravity measurements are shown to be useful validating tools for ocean tides, especially if they are small and/or confined to coastal regions. The low instrumental drift of the SGs also permits to investigate non-tidal effects in time-varying gravity, especially of annual periodicity. Hydrology has also a signature which can be seen in SG measurements as shown by several recent studies. At even lower frequency, there is the Chandler motion of 435-day period which leads to observable gravity changes at the Earth's surface. We finally report on the progress done in the last years in the problem of calibrating/validating space satellite data with SG surface gravity measurements.  相似文献   

On the Accuracy of the Calibration of Superconducting Gravimeters Using Absolute and Spring Sensors: a Critical Comparison     

Umberto Riccardi  Severine Rosat  Jacques Hinderer 《Pure and Applied Geophysics》2012,169(8):1343-1356

Over the past two decades, superconducting gravimeters (SGs) have been a key tool to investigate a number of geophysical processes leading to time-variable gravity changes. As SGs are relative meters, even though they are the most sensitive and stable devices currently available, they need to be accurately calibrated. Each branch of Earth sciences that benefits from high-precision gravity monitoring demands calibration of gravity sensors to accuracy of better than 0.1%. This research deals with a calibration experiment performed at the Strasbourg (France) SG site by means of two FG5 (#206 and #211) absolute gravimeters (AGs) and new-generation spring meters (Scintrex Ltd. Autograv CG-3M and CG5 and Microg-LaCoste gPhone). Our goal is to try to use the newest generation of spring mechanical gravimeters (MGs) for calibrating SGs. We discuss the results in terms of precision and accuracy of the SG calibration by means of different metrological and methodological approaches. With the FG5 #211 we derive scale factors for the SG-GWR C026 located in Strasbourg in agreement with those routinely obtained since 1997 by means of the FG5 #206. This confirms that the estimation of the scale factors is independent of the AG sensor. From a moving-window regression analysis between the synthetic body tides and both the SG and MG gravity records we detect significant fluctuations of the SG scale factors over time due to the instability of the instrumental sensitivity of the MGs. Our main results demonstrate that, owing to the time variability of their sensitivity, the used spring meters, even if well calibrated, cannot be used as a stable reference for SGs. As a result, MGs are not suitable to replace AGs for SG calibration, and we conclude that currently the method using parallel recording with absolute gravity meters is still the most feasible calibration approach for SGs.  相似文献   

Separation of the Geodetic Consequences of Past and Present Ice-Mass Change: Influence of Topography with Application to Svalbard (Norway)     

A. Mémin  J. Hinderer  Y. Rogister 《Pure and Applied Geophysics》2012,169(8):1357-1372

Polar regions such as Greenland, Svalbard and Antarctica are deforming today because of both the present-day ice-mass (PDIM) change of glaciers and the glacial isostatic adjustment (GIA) following the Pleistocene deglaciation. Observations handled in these areas contain both the contributions from the PDIM change and GIA. This study aims at separating them by considering two specific gravity variation-to-vertical displacement ratios. We first review the case of the viscoelastic rebound (GIA) subsequent to the Pleistocene deglaciation leading to a ratio C ^v . The outcome of previous studies is that C ^v is approximately equal to ?0.15?μGal/mm and almost independent of the deglaciation history, ice geometry and viscosity profile of the mantle. Similarly we consider the elastic deformation resulting from PDIM change which leads to a second ratio C ^e,N . Several studies have shown that $C^{e,N} \approx {-}0.26\, \mu$ Gal/mm if one assumes that the changing glaciers are thin layers over the surface of a spherical Earth model. In this case, we show that the separation between the contributions from PDIM change and GIA is unique if both gravity and height changes observations are available at the same station. Next, we focus on C ^e,N and show that according to the deglaciation/glaciation context and from colocated gravity variation and ground vertical velocity measurements one can deduce a range of possible values for C ^e,N . Studying the influence of the topography on C ^e,N we first show that it tends to positive values if most of surrounding ice-mass changes above the altitude of the observation site and to values lower than ?0.26?μGal/mm if changes are below. We next apply our general formalism to the case of the past and PDIM changes in Svalbard, Norway. We compute the ratio C ^e,N at the geodetic observatory at Ny-?lesund and show the influence of the topography of the surrounding glaciers on the measured gravity and uplift rates. We show that if the ice-mass change is spatially uniform, C ^{e, N} does not depend on the speed of ice-mass change, and hence the separation of the contributions from PDIM changes and GIA can still be done univocally. However, if the ice-mass change is not spatially uniform, C ^{e, N} depends on both the speed of ice-mass change and the volume of ice-change rate.  相似文献   

Land Water Storage Changes from Ground and Space Geodesy: First Results from the GHYRAF (Gravity and Hydrology in Africa) Experiment     

J. Hinderer  J. Pfeffer  M. Boucher  S. Nahmani  C. De Linage  J.-P. Boy  P. Genthon  L. Seguis  G. Favreau  O. Bock  M. Descloitres 《Pure and Applied Geophysics》2012,169(8):1391-1410

This paper is devoted to the first results from the GHYRAF (Gravity and Hydrology in Africa) experiment conducted since 2008 in West Africa and is aimed at investigating the changes in water storage in different regions sampling a strong rainfall gradient from the Sahara to the monsoon zone. The analysis of GPS vertical displacement in Niamey (Niger) and Djougou (Benin) shows that there is a clear annual signature of the hydrological load in agreement with global hydrology models like GLDAS. The comparison of GRACE solutions in West Africa, and more specifically in the Niger and Lake Chad basins, reveals a good agreement for the large scale annual water storage changes between global hydrology models and space gravity observations. Ground gravity observations done with an FG5 absolute gravimeter also show signals which can be well related to measured changes in soil and ground water. We present the first results for two sites in the Sahelian band (Wankama and Diffa in Niger) and one (Djougou in Benin) in the Sudanian monsoon region related to the recharge–discharge processes due to the monsoonal event in summer 2008 and the following dry season. It is confirmed that ground gravimetry is a useful tool to constrain local water storage changes when associated to hydrological and subsurface geophysical in situ measurements.  相似文献   

A two-year comparison between the French and Canadian superconducting gravimeter data     

Jacques Hinderer  David Crossley  Hui Xu 《Geophysical Journal International》1994,116(2):252-266

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Premières mesures françaises de gravimétrie absolue dans les régions polaires Antarctique (terre Adélie) et Arctique (Spitzberg)First French measurements of absolute gravity in the Antarctic (Terre Adélie) and Arctic (Spitsbergen) polar regions     

Jacques Hinderer  Martine Amalvict  Bernard Luck 《Comptes Rendus Geoscience》2002,334(11):819-826

This study is devoted to the first French determinations of absolute gravity in the Antarctic (Dumont-d'Urville, Terre Adélie) and Arctic (Ny-Alesund, Spitsbergen) polar regions. The measurements in Dumont-d'Urville were performed in 2000 with the help of the FG5#206 absolute gravimeter belonging to the French geodetic community since beginning 1997; they show a strong noise that causes an uncertainty close to 11 μGal in the determination of the mean gravity value, which will be compared, to a new determination planned for 2005. The Ny-Alesund measurements show on the contrary a noise that, although very variable in time, leads to a gravity determination of better than 5 μGal. The comparison of our value with a previous one two years before suggests a gravity decrease of about 4 μGal which is related to the vertical uplift measured by Very Large Baseline Interferometry (VLBI) at the same site. However, the uncertainty does not allow discriminating between height-to-gravity conversion factors originating from different models. To cite this article: J. Hinderer et al., C. R. Geoscience 334 (2002) 819–826.  相似文献