排序方式： 共有53条查询结果，搜索用时 15 毫秒
1.
A data-driven approach to local gravity field modelling using spherical radial basis functions 总被引：3，自引：0，他引：3
We propose a methodology for local gravity field modelling from gravity data using spherical radial basis functions. The methodology
comprises two steps: in step 1, gravity data (gravity anomalies and/or gravity disturbances) are used to estimate the disturbing
potential using least-squares techniques. The latter is represented as a linear combination of spherical radial basis functions
(SRBFs). A data-adaptive strategy is used to select the optimal number, location, and depths of the SRBFs using generalized
cross validation. Variance component estimation is used to determine the optimal regularization parameter and to properly
weight the different data sets. In the second step, the gravimetric height anomalies are combined with observed differences
between global positioning system (GPS) ellipsoidal heights and normal heights. The data combination is written as the solution
of a Cauchy boundary-value problem for the Laplace equation. This allows removal of the non-uniqueness of the problem of local
gravity field modelling from terrestrial gravity data. At the same time, existing systematic distortions in the gravimetric
and geometric height anomalies are also absorbed into the combination. The approach is used to compute a height reference
surface for the Netherlands. The solution is compared with NLGEO2004, the official Dutch height reference surface, which has
been computed using the same data but a Stokes-based approach with kernel modification and a geometric six-parameter “corrector
surface” to fit the gravimetric solution to the GPS-levelling points. A direct comparison of both height reference surfaces
shows an RMS difference of 0.6 cm; the maximum difference is 2.1 cm. A test at independent GPS-levelling control points, confirms
that our solution is in no way inferior to NLGEO2004. 相似文献
2.
M. C. Santos P. Vaníček W. E. Featherstone R. Kingdon A. Ellmann B. -A. Martin M. Kuhn R. Tenzer 《Journal of Geodesy》2006,80(12):691-704
Following our earlier definition of the rigorous orthometric height [J Geod 79(1-3):82–92 (2005)] we present the derivation and calculation of the differences between this and the Helmert orthometric height, which is embedded in the vertical datums used in numerous countries. By way of comparison, we also consider Mader and Niethammer’s refinements to the Helmert orthometric height. For a profile across the Canadian Rocky Mountains (maximum height of ~2,800 m), the rigorous correction to Helmert’s height reaches ~13 cm, whereas the Mader and Niethammer corrections only reach ~3 cm. The discrepancy is due mostly to the rigorous correction’s consideration of the geoid-generated gravity disturbance. We also point out that several of the terms derived here are the same as those used in regional gravimetric geoid models, thus simplifying their implementation. This will enable those who currently use Helmert orthometric heights to upgrade them to a more rigorous height system based on the Earth’s gravity field and one that is more compatible with a regional geoid model. 相似文献
3.
Explicit formula for the geoid-quasigeoid separation 总被引：1，自引：0，他引：1
The explicit formula for the geoid-to-quasigeoid correction is derived in this paper. On comparing the geoidal height and
height anomaly, this correction is found to be a function of the mean value of gravity disturbance along the plumbline within
the topography. To evaluate the mean gravity disturbance, the gravity field of the Earth is decomposed into components generated
by masses within the geoid, topography and atmosphere. Newton’s integration is then used for the computation of topography-and
atmosphere-generated components of the mean gravity, while the combined solution for the downward continuation of gravity
anomalies and Stokes’ boundary-value problem is utilized in computing the component of mean gravity disturbance generated
by mass irregularities within the geoid. On application of this explicit formulism a theoretical accuracy of a few millimetres
can be achieved in evaluation of the geoid-to-quasigeoid correction. However, the real accuracy could be lower due to deficiencies
within the numerical methods and to errors within the input data (digital terrain and density models and gravity observations). 相似文献
4.
Emanuele Perinati Marco Barbera Sebastian Diebold Alejandro Guzman Andrea Santangelo Chris Tenzer 《Experimental Astronomy》2017,44(3):387-399
We present a preliminary assessment of the non-X-ray background for the WFI on board ATHENA conducted at IAAT in the context of the collaborative background and radiation damage working group activities. Our main result is that in the baseline configuration originally assumed for the camera the requirement on the level of non-X-ray background could not be met. In light of the results of Geant4 simulations we propose and discuss a possible optimization of the camera design and pinpoint some open issues to be addressed in the next phase of investigation. One of these concerns the possible contribution to the non-X-ray background from soft protons and ions funneled to the focal plane through the optics. This is not quantified at this stage, here we just briefly report on our ongoing activities aimed at validating the mechanisms of proton scattering at grazing incidence. 相似文献
5.
6.
In global studies investigating the Earth’s lithospheric structure, the spectral expressions for the gravimetric forward and inverse modeling of the global gravitational and crustal structure models are preferably used, because of their numerical efficiency. In regional studies, the applied numerical schemes typically utilize the expressions in spatial form. Since the gravity-gradient observations have a more localized support than the gravity measurements, the gravity-gradient data (such as products from the Gravity field and steady-state Ocean Circulation Explorer - GOCE - gravity-gradiometry satellite mission) could preferably be used in regional studies, because of reducing significantly the spatial data-coverage required for a regional inversion or interpretation. In this study, we investigate this aspect in context of a regional Moho recovery. In particular, we compare the numerical performance of solving the Vening Meinesz-Moritz’s (VMM) inverse problem of isostasy in spectral and spatial domains from the gravity and (vertical) gravity-gradient data. We demonstrate that the VMM spectral solutions from the gravity and gravity-gradient data are (almost) the same, while the VMM spatial solutions differ from the corresponding spectral solutions, especially when using the gravity-gradient data. The validation of the VMM solutions, however, reveals that the VMM spatial solution from the gravity-gradient data has a slightly better agreement with seismic models. A more detailed numerical analysis shows that the VMM spatial solution formulated for the gravity gradient is very sensitive to horizontal spatial variations of the vertical gravity gradient, especially in vicinity of the computation point. Consequently, this solution provides better results in regions with a relatively well-known crustal structure, while suppressing errors caused by crustal model uncertainties from distant zones. Based on these findings we argue that the gravity-gradient data are more suitable than the gravity data for a regional Moho recovery. 相似文献
7.
8.
We derive expressions for computing the gravitational field (potential and its radial derivative) generated by an arbitrary
homogeneous or laterally varying density contrast layer with a variable depth and thickness based on methods for a spherical
harmonic analysis and synthesis of gravity field. The newly derived expressions are utilised in the gravimetric forward modelling
of major known density structures within the Earth’s crust (excluding the ocean density contrast) beneath the geoid surface.
The gravitational field quantities due to the sediments and crust components density contrasts, shown in numerical examples,
are computed using the 2 × 2 arc-deg discrete data from the global crustal model CRUST2.0. These density contrasts are defined
relative to the adopted value of the reference crustal density of 2670 kgm−3. All computations are realised globally on a 1 × 1 arc-deg geographical grid at the Earth’s surface. The maxima of the gravitational
signal due to the sediments density contrast are mainly along continental shelf regions with the largest sedimentary deposits.
The corresponding maxima due to the consolidated crust components density contrast are over areas of the largest continental
crustal thickness with variable geological structure. 相似文献
9.
The gravitational signal of the upper mantle density structures is investigated in the refined gravity data which are corrected for the gravitational contributions of the crust density structures and the Moho geometry. The gravimetric forward modeling is applied to compute these refined gravity data globally on a 1 × 1 arcdeg grid using the global geopotential model (EGM2008), the global topographic/bathymetric model (DTM2006.0) including the ice-thickness data, and the global crustal model (CRUST2.0). The characteristics of the upper mantle density structures are further analyzed in association with the Moho parameters (i.e., Moho depths and density contrast). The 1 × 1 arcdeg global data of the Moho parameters are estimated by applying the combined least-squares approach based on solving Moritz’s generalization of the Vening–Meinesz inverse problem of isostasy. The refined gravity data exhibit mainly the mantle lithosphere structures attributed to the global mantle convection. A significant correlation found over oceans between the refined gravity data and the Moho density contrast is explained by the increasing density of the oceanic lithosphere with age. Despite the lithosphere structures attributed to the global mantle convection are confirmed also in the refined gravity data over continents, the significant correlation between the refined gravity data and the Moho parameters is in this case absent. Instead, the significant proportion of lateral variations of the Moho density contrast within the continental lithosphere is attributed to the depth-dependant density changes due to pressure and thermal gradient. 相似文献
10.
On the accuracy of the bathymetry-generated gravitational field quantities for a depth-dependent seawater density distribution 总被引：1，自引：0，他引：1
In geophysical studies investigating the lithosphere structure, the gravitational field generated by the ocean density contrast
(i.e., bathymetry-generated gravitational field) represents a significant amount of the signal to be modelled and subsequently
removed from the Earth’s gravity field. The ocean density contrast is typically calculated as the difference between the mean
density values of the Earth’s crust and seawater. The approximation of the actual seawater density distribution by its mean
value yields relative errors up to about 2% in computed quantities of the gravitational field. To reduce these errors, a more
realistic model of the seawater density distribution is utilized based on the analysis of existing oceanographic data of salinity,
temperature, and pressure (depth). We study the accuracy of the bathymetry-generated gravitational field quantities formulated
for a depth-dependent model of the seawater density distribution. This density distribution approximates the seawater density
variations due to an increasing pressure with depth, whereas smaller lateral density variations caused by salinity, temperature,
and other oceanographic factors are not taken into consideration. The error analysis reveals that the approximation of the
seawater density by the depth-dependent density model reduces the maximum errors to less than 0.6%. The corresponding depth-averaged
errors are below 0.1%. The depth-dependent seawater density model is further facilitated in expressions for computing the
bathymetry-generated gravitational field quantities by means of the spherical bathymetric (ocean bottom depth) functions.
The numerical realization reveals large differences in the results obtained with and without consideration of the depth-dependent
seawater density distribution. The maxima of absolute differences reach 201 m2/s2 and 16.5 mGal in computed values of the potential and attraction, respectively. The application of the depth-dependent seawater
density model thus significantly improves the accuracy in the forward modelling of the bathymetric gravitational field quantities. 相似文献