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81.
Jean-François Crétaux Stephane Calmant Vladimir Romanovski Anton Shabunin Florent Lyard Muriel Bergé-Nguyen Anny Cazenave Fabrice Hernandez Felix Perosanz 《Journal of Geodesy》2009,83(8):723-735
Altimetry missions such as Topex/Poseidon, Jason-1, GFO and ENVISAT have been widely used in the continental domain over lakes,
rivers and wetland although they were mostly dedicated to oceanic studies. Knowledge of the instrumental biases is a key issue.
Numerous sites have been dedicated to calibration purposes, either in the oceanic domain (Harvest offshore platform in California,
Corsica, Bass Strait in Australia) or over lakes (Lake Erie in United States). A new site (Lake Issykkul in Kirghizstan) is
proposed for calibration in the continental domain. This lake is covered by past (T/P) and current radar altimetry satellites
(Jason-1, T/P, GFO, and ENVISAT). Several in situ water levels and local meteorological variables are available at the site.
Located in a mountainous area, it offers an opportunity for calibration far away from all other existing sites and very different
environment contexts. Two GPS campaigns have been conducted on the lake in 2004 and in 2005. They consisted of cruises with
stations installed onboard a boat following the satellite ground tracks, and onshore settings. This enabled estimating a bias
for each altimeter and each tracking algorithm available. Biases obtained for Envisat, GFO, T/P and Jason-1 using the default
ocean tracker (respectively, 48.1 ± 6.6, 7.5 ± 4.0, 0 ± 4.3 and 7.0 ± 5.5 cm) agree with biases published at the other calibration
sites. For Jason-1, there is a significant disagreement with results obtained in the ocean field (7 cm instead of 13 cm) but
is coherent with bias obtained on the Lake Erie site. Erroneous estimates of the sea state bias correction from non-oceanic-like
waveforms is discussed as a possible explanation. Errors in the ionospheric, wet and dry tropospheric corrections for the
continental domain are also highlighted and quantified. 相似文献
82.
83.
Christian M. Boily Jean-Julien Fleck Ariane Lançon Florent Renaud 《Astrophysics and Space Science》2009,324(2-4):265-269
We point out a strong time evolution of the mass-to-light conversion factor, η, commonly used to estimate masses of unresolved star clusters from observed cluster spectrophotometric measures. We present a series of gas-dynamical models, coupled with the Cambridge stellar evolution tracks, to compute line-of-sight velocity dispersions and half-light radii weighted by the luminosity. We explore a range of initial conditions, varying in turn the cluster mass and/or density, and the stellar population’s initial mass function. We find that η, and hence the estimated cluster mass, may increase by as much as a factor of three over time-scales of 50 million yr. We apply these results to an hypothetic cluster mass distribution function (d.f.), and show that the d.f. shape may be strongly affected at the low-mass end by this effect. Fitting truncated isothermal (Michie–King) models to the projected light profile leads to over-estimates of the concentration parameter, c, of δ c≈0.3 compared to the same functional fit applied to the projected mass density. 相似文献
84.
85.
86.
87.
Florent Brenguier Daniel Clarke Yosuke Aoki Nikolai M. Shapiro Michel Campillo Valérie Ferrazzini 《Comptes Rendus Geoscience》2011,343(8-9):633-638
In this article, we summarize some recent results of measurements of temporal changes of active volcanoes using seismic noise cross-correlations. We first present a novel approach to estimate volcano interior temporal seismic velocity changes. The proposed method allows to measure very small velocity changes (≈ 0.1%) with a time resolution as small as one day. The application of that method to Piton de la Fournaise Volcano (La Réunion Island) shows velocity decreases preceding eruptions. Moreover, velocity changes from noise cross-correlations over 10 years allow to detect transient velocity changes that could be due to long-lasting intrusions of magma without eruptive activity or to pressure buildup associated to the replenishing of the magma reservoir. We also present preliminary results of noise cross-correlation waveform perturbation associated with the occurrence of dike injection and volcanic eruption. We show that such an analysis leads us to locate the areas of dike injection and eruptive fissures at Piton de la Fournaise Volcano. These recent results suggest that monitoring volcanoes using seismic noise correlations should improve our ability to forecast eruptions, their intensity and thus potential environmental impact. 相似文献
88.
89.
Florent Deleflie Gilles Métris Pierre Exertier 《Celestial Mechanics and Dynamical Astronomy》2006,94(1):105-134
This paper presents an analytic solution of the equations of motion of an artificial satellite, obtained using non singular
elements for eccentricity. The satellite is under the influence of the gravity field of a central body, expanded in spherical
harmonics up to an arbitrary degree and order. We discuss in details the solution we give for the components of the eccentricity
vector. For each element, we have divided the Lagrange equations into two parts: the first part is integrated exactly, and
the second part is integrated with a perturbation method. The complete solution is the sum of the so-called “main” solution
and of the so-called “complementary” solution. To test the accuracy of our method, we compare it to numerical integration
and to the method developed in Kaula (Theory of Satellite Geodesy, Blaisdell publ. Co., New York. 1966), expressed in classical
orbital elements. For eccentricities which are not very small, the two analytical methods are almost equivalent. For low eccentricities,
our method is much more accurate. 相似文献
90.
B. V. Jackson J. A. Boyer P. P. Hick A. Buffington M. M. Bisi D. H. Crider 《Solar physics》2007,241(2):385-396
Interplanetary Scintillation (IPS) allows observation of the inner heliospheric response to corotating solar structures and
coronal mass ejections (CMEs) in scintillation level and velocity. With colleagues at STELab, Nagoya University, Japan, we
have developed near-real-time access of STELab IPS data for use in space-weather forecasting. We use a 3D reconstruction technique
that produces perspective views from solar corotating plasma and outward-flowing solar wind as observed from Earth by iteratively
fitting a kinematic solar wind model to IPS observations. This 3D modeling technique permits reconstruction of the density
and velocity structure of CMEs and other interplanetary transients at a relatively coarse resolution: a solar rotational cadence
and 10° latitudinal and longitudinal resolution for the corotational model and a one-day cadence and 20° latitudinal and longitudinal
heliographic resolution for the time-dependent model. This technique is used to determine solar-wind pressure (“ram” pressure)
at Mars. Results are compared with ram-pressure observations derived from Mars Global Surveyor magnetometer data (Crider et al.
2003, J. Geophys. Res.
108(A12), 1461) for the years 1999 through 2004. We identified 47 independent in situ pressure-pulse events above 3.5 nPa in the Mars Global Surveyor data in this time period where sufficient IPS data were available. We detail the large pressure pulse observed at Mars in
association with a CME that erupted from the Sun on 27 May 2003, which was a halo CME as viewed from Earth. We also detail
the response of a series of West-limb CME events and compare their response observed at Mars about 160° west of the Sun – Earth
line by the Mars Global Surveyor with the response derived from the IPS 3D reconstructions. 相似文献