The search for weak harmonic signals in a spectrum with application to gravity data     

Nicolas Florsch  Hilaire Legros  Jacques Hinderer 《Physics of the Earth and Planetary Interiors》1995,90(3-4)

When considering the search for discovery or amplitude estimation of a spectral line with a probabilistic approach, great attention must be paid to the meaning of each step. We give the probability law for the amplitude of a spectral peak in the presence of random noise appearing in a periodogram and discuss the effective probability of the existence of the corresponding wave. We find that the estimated amplitude of a spectral peak is biased and should be corrected when the signal-to-noise ratio is small. As a first application to gravity data, it results in a re-estimation of the gravimetric amplitude factors (delta factors) provided by least-squares tidal analysis. We also estimate the probability of observing a spectral line above a given level in the spectrum of a purely random noise. This allows us to compute for given spectrum the number of peaks expected to overcross the classical levels used in statistical analysis (like nσ, where σ is the standard deviation of the temporal noise distribution and n is an integer with typical values equal to 2 or 3). A specific application to real data is investigating the gravity spectrum derived from a 5 year record of the French superconducting gravimeter and we show that the predicted statistics are indeed in agreement with the observations. We also show the statistical consequence of using longer observing periods to obtain the spectral estimations. The problem of detecting translational motion of the Earth's solid inner core (Slichter modes) in a gravity spectrum is analyzed and the probabilities of having a triplet of random peaks thresholding specific levels in a given frequency window are computed. We show that, in the case of a typical gravity spectrum (1 year of hourly data and a frequency window of 0.03 cycle h⁻¹), the probability of having a random set of three peaks exceeding a level of 3 σ, is very high. This emphasizes the need for a very careful analysis of spectral lines before inferring the existence of a true physical signal.  相似文献   

Core-mantle interactions     

K. D. Aldridge  J. Bloxham  V. Dehant  D. Gubbins  R. Hide  J. Hinderer  K. A. Hutcheson  D. Jault  C. A. Jones  H. Legros  J. -L. Le Mouël  D. Lloyd  J. M. Wahr  K. A. Whaler  K. Zhang 《Surveys in Geophysics》1990,11(4):329-353

Several aspects of core-mantle interactions were considered during a Royal Astronomical Society Discussion Meeting on 12th May 1989, including modelling the geomagnetic field at the core surface, the morphology of the field between 1600 and 1820 AD, dynamo theory, Taylor's constraint, fluid motions at the top of the core that reproduce the observed secular variation, pressure coupling between the core and mantle and its geophysical consequences, topographic core-mantle coupling, angular momentum transfer at the core-mantle interface, the detection and implications of core oscillations, particularly those with associated fluctuations in the Earth's rotation rate, and the seismological determination of the core-mantle boundary topography from lateral inhomogeneities in the mantle.  相似文献   

A simple method to retrieve the complex eigenfrequency of the Earth's nearly diurnal-free wobble; application to the Strasbourg superconducting gravimeter data     

Nicolas Florsch  Fréderic Chambat  Jacques Hinderer  Hilaire Legros 《Geophysical Journal International》1994,116(1):53-63

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Static displacement fields due to a seismic source in a nonhomogeneous (dimorphic) medium. Geophysical applications     

Martine Amalvict  Hilaire Legros 《Pure and Applied Geophysics》1983,121(5-6):817-834

A new method for finding static displacement fields due to seismic sources (forces or dislocations) in a nonhomogeneous medium (called “dimorphic”) is presented. Previously known results can be easily calculated, as well as new results for sources located at the interface between two media with different elastic properties. The ratio of displacement magnitudes in homogeneous and dimorphic media, which can be as great as 15%, is calculated. Consequences for the seismic moment and some other geophysical applications are discussed.  相似文献   

Using importers’ windfall savings from oil subsidy reform to enhance international cooperation on climate policies     

Michael Jakob  Jérôme Hilaire 《Climatic change》2015,131(4):465-472

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Modeling tropospheric wet delays with dense and sparse network configurations for PPP-RTK     

de Oliveira  P. S.  Morel  L.  Fund  F.  Legros  R.  Monico  J. F. G.  Durand  S.  Durand  F. 《GPS Solutions》2017,21(1):237-250

GPS Solutions - Precise Point Positioning (PPP) is a well-known technique of positioning by Global Navigation Satellite Systems (GNSS) that provides accurate solutions. With the availability of...  相似文献   

Correlation between some major geological events and resonances between the free core nutation and luni-solar tidal waves     

Marianne Greff-Lefftz  & Hilaire Legros 《Geophysical Journal International》1999,139(1):131-151

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On the calibration of a superconducting gravimeter using absolute gravity measurements   总被引：4，自引：0，他引：4  

J. Hinderer  N. Florsch  J. Mäkinen  H. Legros  J. E. Faller 《Geophysical Journal International》1991,106(2):491-497

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Non-linear equations for the rotation of a viscoelastic planet taking into account the influence of a liquid core     

M. Lefftz  H. Legros  J. Hinderer 《Celestial Mechanics and Dynamical Astronomy》1991,52(1):13-43

Non-linear equations governing the temporal evolution of the vector of instantaneous rotation are developed for an Earth with a homogeneous mantle having a viscoelastic Maxwell rheology and with a homogeneous inviscid fluid core.This general theory is investigated using the angular momentum theorem applied to the coupled core-mantle system. It allows to study the influence upon the planetary rotation of a quasi-rigid rotational motion in the liquid core. It also enables to investigate the consequences of excitation sources (e.g. pressure), located at the core-mantle interface. Especially, the influence of viscoelastic variations in the inertia tensors resulting from the rotation itself or from various excitation sources are detailed with the help of a Love number formalism. The equations of the linear theory for an elastic Earth with a liquid core, and the non-linear theory for a viscous planet with a quasi-fluid behavior are shown to be particular cases of our generalized system of equations. Some planetological applications may be derived from the quasi-fluid approximation.  相似文献   

Seasonal and monthly hydrological budgets of a fen‐dominated forested watershed,James Bay region,Quebec     

Sandra Proulx‐McInnis  André St‐Hilaire  Alain N. Rousseau  Sylvain Jutras  Gwenael Carrer  Grégor Levrel 《水文研究》2013,27(10):1365-1378

The hydrology of Quebec, Canada, boreal fens is poorly documented. Many peatlands are located in watersheds with impounded rivers. In such cases, their presence influences reservoir inflows. In recent years, some fens have been subjected to an increase of their wet area, a sign that they may be evolving towards an aquatic ecosystem. This dynamic process is called aqualysis. This article presents the seasonal and monthly hydrological budgets of a small watershed including a highly aqualysed fen (James Bay region). The monitoring of precipitation (P), runoff (Q) and groundwater levels (WL) was conducted during the ice‐free season. Three semiempirical equations (Thornthwaite, Priestley–Taylor and Penman–Monteith) were used and compared to calculate potential evapotranspiration. The first two equations, having fewer parameters, estimate higher potential evapotranspiration values than the third equation. The use of pressure‐level gauges installed in wells, for the calculation of peatland water storage, is inconclusive. Swelling of peat, peat decomposition and plant composition could be responsible for nonnegligible amounts of absorbed water, which are not entirely accounted for by well levels. The estimation of peat matrix water storage is potentially the largest source of error and the limiting factor to calculate water balances in this environment. The results show that the groundwater level and the water storage vary depending on the season and especially after a heavy rainfall. Finally, the results illustrate the complexity of water routing through the site and thus raise several questions to be resolved in the future. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献