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2.
G. Bourda 《Journal of Geodesy》2008,82(4-5):295-305
The temporal variations of the Earth’s gravity field, nowadays routinely determined from satellite laser ranging (SLR) and
GRACE (Gravity Recovery And Climate Experiment), are related to changes in the Earth’s rotation rate through the Earth’s inertia
tensor. We study this connection from actual data by comparing the traditional length-of-day (LOD) measurements provided by
the International Earth Rotation and Reference Systems Service (IERS) to the variations of the degree-2 and order-0 Stokes
coefficient of the gravity field determined from fitting the orbits of the LAGEOS-1 and −2 satellites since 1985. The two
series show a good correlation (0.62) and similar annual and semi-annual signals, indicating that the gravity-field-derived
LOD is valuable. Our analysis also provides evidence for additional signals common to both series, especially at a period
near 120 days, which could be due to hydrological effects. 相似文献
3.
P. Moore 《Journal of Geodesy》1987,61(3):223-234
Starlette was launched in 1975 in order to study temporal variations in the Earth’s gravity field; in particular, tidal and
Earth rotation effects. For the period April 1983 to April 1984 over12,700 normal points of laser ranging data to Starlette have been sub-divided into49 near consecutive 5–6 day arcs. Normal equations for each arc as obtained from a least-squares data reduction procedure, were
solved for ocean tidal parameters along with other geodetic and geodynamic parameters. The tidal parameters are defined relative
to Wahr’s body tides and Wahr’s nutation model and show fair agreement with other satellite derived results and those obtained
from spherical harmonic decomposition of global ocean tidal models. 相似文献
4.
K. Lambeck 《Journal of Geodesy》1971,45(3):263-281
The methods of using earth satellites for determining the motion of the earth’s axis of rotation and of the earth’s principal
axis of maximum inertia are discussed.
Some simple formulae are also presented for evaluating the influence of various error sources in the orbital calculations
on the pole coordinates and these offer some explanations of the frequencies found in the spectrum of the pole coordinates
obtained by Anderle and Beuglass (1970). Initial calculations with existing laser data were attempted but the results were
quite unsatisfactory due to the poor distribution of the data along the orbit. Some conclusions have however been drawn from
these calculations that may be useful for future studies when better distributed data becomes available. 相似文献
5.
Gravity-dependent signal path variation in a large VLBI telescope modelled with a combination of surveying methods 总被引:4,自引:3,他引:1
The very long baseline interferometry (VLBI) antenna in Medicina (Italy) is a 32-m AZ-EL mount that was surveyed several times,
adopting an indirect method, for the purpose of estimating the eccentricity vector between the co-located VLBI and Global
Positioning System instruments. In order to fulfill this task, targets were located in different parts of the telescope’s
structure. Triangulation and trilateration on the targets highlight a consistent amount of deformation that biases the estimate
of the instrument’s reference point up to 1 cm, depending on the targets’ locations. Therefore, whenever the estimation of
accurate local ties is needed, it is critical to take into consideration the action of gravity on the structure. Furthermore,
deformations induced by gravity on VLBI telescopes may modify the length of the path travelled by the incoming radio signal
to a non-negligible extent. As a consequence, differently from what it is usually assumed, the relative distance of the feed
horn’s phase centre with respect to the elevation axis may vary, depending on the telescope’s pointing elevation. The Medicina
telescope’s signal path variation ΔL increases by a magnitude of approximately 2 cm, as the pointing elevation changes from horizon to zenith; it is described
by an elevation-dependent second-order polynomial function computed as, according to Clark and Thomsen (Techical report, 100696,
NASA, Greenbelt, 1988), a linear combination of three terms: receiver displacement ΔR, primary reflector’s vertex displacement ΔV and focal length variations ΔF. ΔL was investigated with a combination of terrestrial triangulation and trilateration, laser scanning and a finite element model
of the antenna. The antenna gain (or auto-focus curve) ΔG is routinely determined through astronomical observations. A surprisingly accurate reproduction of ΔG can be obtained with a combination of ΔV, ΔF and ΔR. 相似文献
6.
M. S. Petrovskaya 《Journal of Geodesy》1979,53(1):37-51
Summary The possibility of improving the convergence of Molodensky’s series is considered. Then new formulas are derived for the solution
of the geodetic boundary value problem. One of them presents an expression for the boundary condition which involves a linear
combination of Stokes’ constants and surface gravity anomalies. This differs from the usually used relation by the appearance
of additional terms dependent on second order terns with respect to the elevations of the earth’s surface. The formulas are
derived for Stokes’ constants and the anomalous potential in terms of surface anomalies. As compared to the Taylor’s series
of Molodensky, they are presented in the form of surface harmonic series. Due regard is made to the earth’s oblateness, in
addition to the terrain topography. 相似文献
7.
移动激光扫描技术是从上世纪90年代初逐步发展起来的一门测绘技术,也是当今测绘界最为前沿的技术之一,可用于工程测量和制图等诸多领域。地面3D激光扫描仪具有测量速度快,精度高等优点。本文以奥地利RIEGL公司的地面三维激光扫描仪VZ400为例,研究将其作为移动测量系统的主要传感器所涉及的关键技术,包括联机控制、时间基准统一和空间基准统一三个方面:解析了激光扫描仪的接口定义,并结合联机控制的开发库——RiVLIB实现的仪器的联机控与数据通信;给出了基于GPS秒脉冲信号的时间同步原理,实现了系统时间基准的传递与统一;分析了移动测量系统中的坐标系,并根据地面三维激光扫描仪的实际情况,构建了单站的参数标定模型。通过本文的研究与实验,使测量系统实现常见移动测量的二维帧扫描模式以及针对重点区域的三维全景扫描模式,同时,当它闲置时还可将激光扫描仪拆卸进行静态的扫描,丰富了系统的测量方式,提高了系统的适应性与使用效率。 相似文献
8.
Ravindra Babu 《GPS Solutions》2005,9(3):240-242
This column provides the Web-based GPS resources and their technical background information. Its purpose is to inform the
reader about the data, software, electronic documents that are available online. This column is coordinated by Dr. Jinling
Wang, The University of New South Wales, Sydney. Comments and suggestions are appreciated (jinling.wang@unsw.edu.au). In this
issue’s column, Mr. Ravindra Babu introduces the online resources on software GPS receivers. 相似文献
9.
The Spaceborne Laser Ranging System is a proposed short pulse laser on board an orbiting spacecraft.1,2,3,4 It measures the distance between the spacecraft and many laser retroreflectors (targets) deployed on the Earth’s surface.
The precision of these range measurements is assumed to be about ±2 cm (M. W. Fitzmaurice, private communication). These measurements are then used together with the orbital dynamics of the spacecraft, to derive
the relative position of the laser ground targets. Assuming a six day observing period with 50% cloud cover, uncertainties
in the baseline for target separations of 50 km to 1200 km were estimated to be on the order of 1 to 3 cm and the corresponding
values in the vertical direction, ranged from 1 cm to 12 cm. By redetermining the measurements of the relative target positions,
the estimated precision in the baseline for a target separation of 50 km is less than 0.3 cm and for a separation of 1200
km is less than 1 cm. In the vertical direction, the estimated precision ranged from 0.4 cm to 4.0 cm respectively. As a result
of the repeated estimation of the relative laser target positions, most of the non-temporal effects of error sources as exemplified
by the errors in geopotential are reduced.
The Spaceborne Laser Ranging System’s capability of determining baselines to a high degree of precision provides a measure
of strain and strain rate as shown byCohen, 1979. These quantities are essential for crustal dynamic studies which include determination and monitoring of strain near
seismic zones, land subsidence, and edifice building preceding volcanic eruptions. It is evident that such a system can also
be used for geodetic surveys where such precisions are more than adquate. 相似文献
10.
FENG Wenhao LI Xin 《地球空间信息科学学报》2001,4(1):28-36
1 IntroductionInourcountry ,thesurveyingworkonindustrialobjectshave graduallyincreased .Thoseindustrialobjectsincluderailwayandhighwaytunnels,vari ousoilandgascans ,variousaircraft,shellofcars,largemilitaryantennausedforscoutingstealthplane ,ship ,internalst… 相似文献
11.
The problems of the earth’s gravity fields’ visualization are both focus and puzzle currently. Aiming at multiresolution rendering,
modeling of the Earth’s gravity fields’ data is discussed in the paper by using LOD algorithm based on Quad Tree. First, this
paper employed the method of LOD based on Quad Tree to divide up the regional gravity anomaly data, introduced the combined
node evaluation system that was composed of viewpoint related and roughness related systems, and then eliminated the T-cracks
that appeared among the gravity anomaly data grids with different resolutions. The test results demonstrated that the gravity
anomaly data grids’ rendering effects were living, and the computational power was low. Therefore, the proposed algorithm
was a suitable method for modeling the gravity anomaly data and has potential applications in visualization of the earth’s
gravity fields. 相似文献
12.
Dimitri G. Vlachos 《Journal of Geodesy》1970,44(3):213-223
Résumé Dans cette étude on expose une adaptation de la méthode des directions —pour la compensation d’un réseau de triangulation—aux
possibilités de l’ordinateur électronique. On présente les formules par lesquelles on calcule les coefficients des inconnues
dans les équations de condition (équations aux angles et équations aux c?tés) et on dresse leur matrice. Ensuite on traite
de la formation de la matrice des coefficients des équations normales et son inversion, qui fournit les quantités corrélatives
de Lagrange. Enfin, après avoir déterminé les corrections à apporter aux directions observées, on calcule l’erreur moyenne
quadratique d’une observation isolée et l’erreur moyenne de chacune des directions compensées.
Summary In this study, an adaptation to the computers’ possibilities, regarding the method of directions, is disclosed in order to realise the adjustment of triangulation nets. The computing formulae of the coefficients of the unknown quantities in the condition equations and the creation of their matrix are given herebelow. The treatment leading towards the construction of the matrix of normal equations and its inversion, that furnishes Lagrange’s quantities, follows. After the computation of the corrections applied on the observed directions, the mean error of a single observation and the mean error of every adjusted direction are determined. The study is executed in such a way that it can be included in only one programme for automatic computation.相似文献
13.
The consistency of the Chang’E-1 and SELENE reference frames as realized by the footprint positions of laser altimetry measurements
of the lunar surface during both missions was analyzed using a global 12-parameter model for small (with respect to unity)
deformations and rigid body motions. The rigid body motion and deformation parameters between the two reference frames estimated
from nearly-colocated without tie measurements are found to be consistent, i.e., nearly zero for the estimates of the translations,
rotations and shear parameters. However, the estimated three strain parameters, which are similar in magnitude and sign, reveal
a prominent scale difference, between the Chang’E-1 and SELENE reference frames, of about 0.9 × 10−5. The scale difference can be attributed to calibration of the data sets using the known coordinates of the lunar laser ranging
stations all located on the near side of the Moon. 相似文献
14.
We present an alternate mathematical technique than contemporary spherical harmonics to approximate the geopotential based
on triangulated spherical spline functions, which are smooth piecewise spherical harmonic polynomials over spherical triangulations.
The new method is capable of multi-spatial resolution modeling and could thus enhance spatial resolutions for regional gravity
field inversion using data from space gravimetry missions such as CHAMP, GRACE or GOCE. First, we propose to use the minimal
energy spherical spline interpolation to find a good approximation of the geopotential at the orbital altitude of the satellite.
Then we explain how to solve Laplace’s equation on the Earth’s exterior to compute a spherical spline to approximate the geopotential
at the Earth’s surface. We propose a domain decomposition technique, which can compute an approximation of the minimal energy
spherical spline interpolation on the orbital altitude and a multiple star technique to compute the spherical spline approximation
by the collocation method. We prove that the spherical spline constructed by means of the domain decomposition technique converges
to the minimal energy spline interpolation. We also prove that the modeled spline geopotential is continuous from the satellite
altitude down to the Earth’s surface. We have implemented the two computational algorithms and applied them in a numerical
experiment using simulated CHAMP geopotential observations computed at satellite altitude (450 km) assuming EGM96 (n
max = 90) is the truth model. We then validate our approach by comparing the computed geopotential values using the resulting
spherical spline model down to the Earth’s surface, with the truth EGM96 values over several study regions. Our numerical
evidence demonstrates that the algorithms produce a viable alternative of regional gravity field solution potentially exploiting
the full accuracy of data from space gravimetry missions. The major advantage of our method is that it allows us to compute
the geopotential over the regions of interest as well as enhancing the spatial resolution commensurable with the characteristics
of satellite coverage, which could not be done using a global spherical harmonic representation.
The results in this paper are based on the research supported by the National Science Foundation under the grant no. 0327577. 相似文献
15.
M. S. Petrovskaya 《Journal of Geodesy》1979,53(3):259-271
Summary The geopotential on and outside the earth is represented as a series in surface harmonics. The principal terms in it correspond
to the solid harmonics of the external potential expansion with the coefficients being Stokes’ constantsC
nm
andS
nm
. The additional terms which occur near the earth’s surface due to its non-sphericity and topography are expressed in terms
of Stokes’ constants too. This allows performing downward continuation of the potential derived from satellite observations.
In the boundary condition which correlates Stokes’ constants and the surface gravity anomalies there occur additional terms
due to the earth’s non-sphericity and topography. They are expressed in terms of Stokes’ constants as well. This improved
boundary condition can be used for upward and downward continuations of the gravity field. Simple expressions are found representingC
nm
andS
nm
as explicit functions of the surface anomalies and its derivatives. The formula for the disturbing potential on the surface
is derived in terms of the surface anomalies. All the formulas do not involve the earth’s surface in clinations. 相似文献
16.
The robustness of an outlier detection method strongly depends on the weights of observations, i.e., the type of the stochastic
model applied (homoscedasticity, heteroscedasticity and heterogeneousness). In this paper, we have investigated how the reliability
of the robust methods and tests for outliers changes depending on the weights of the observations in geodetic networks. Furthermore,
the contribution of the directions and distances to horizontal control network with regard to reliability are investigated
separately. The concept of a breakdown point is used as a global measure of robustness against outliers. The mean success
rate (MSR) is found to be a practical tool for confirming the breakdown point. Many different “good” data samples are generated
for each network and then deliberately contaminated using a Monte-Carlo simulation. Six robust methods and Baarda’s test are
applied to the corrupted samples and the degree of corruption is varied. The performance of each method is measured using
both local and global MSRs. Our research shows: (1) The MSRs of Baarda’s test change depending on the strength of the heteroscedasticity,
but do not change for trilateration and leveling networks, (2) the global MSRs of robust methods do not differ considerably
from the local ones 相似文献
17.
Studies on small-world networks have received intensive interdisciplinary attention during the past several years. It is well-known
among researchers that a small-world network is often characterized by high connectivity and clustering, but so far there
exist few effective approaches to evaluate small-world properties, especially for spatial networks. This paper proposes a
method to examine the small-world properties of spatial networks from the perspective of network autocorrelation. Two network
autocorrelation statistics, Moran’s I and Getis–Ord’s G, are used to monitor the structural properties of networks in a process of “rewiring” networks from a regular to a random
network. We discovered that Moran’s I and Getis–Ord’s G tend to converge and have relatively low values when properties of small-world networks emerge. Three transportation networks
at the national, metropolitan, and intra-city levels are analyzed using this approach. It is found that spatial networks at
these three scales possess small-world properties when the correlation lag distances reach certain thresholds, implying that
the manifestation of small-world phenomena result from the interplay between the network structure and the dynamics taking
place on the network.
相似文献
18.
A simulation study of multi-beam altimetry for lunar reconnaissance orbiter and other planetary missions 总被引:4,自引:4,他引:0
The combined use of altimetry, Earth-based Doppler and Earth-based range measurements in the lunar reconnaissance orbiter
(LRO) mission (Chin et al. in Space Sci Rev 129:391–419, 2007) has been examined in a simulation study. It is found that in
the initial phases of the mission orbit and altimeter geolocation accuracies should be better than 10 m in the radial component
and 60 m overall. It is demonstrated that LRO’s precise 1-way laser range measurement from Earth-based stations (Smith et
al. in Proceedings of the 15th International Laser Ranging Workshop, Canberra, Australia, October 15–20, 2006) will be useful
for gravity recovery. The advantages of multiple laser beams are demonstrated for altimeter calibration, orbit determination
and gravity recovery in general planetary settings as well as for LRO. 相似文献
19.
R. H. Rapp 《Journal of Geodesy》1971,45(3):283-297
The undulations of the geoid may be computed from spherical harmonic potential coefficients of the earth’s gravitational field.
This paper examines three procedures that reflect various points of view on how this computation should be carried out. One
method requires only the flattening of a reference ellipsoid to be defined while the other two methods require a complete
definition of the parameters of the ellipsoid. It was found that the various methods give essentially the same undulations
provided that correct parameters are chosen for the reference ellipsoid. A discussion is given on how these parameters are
chosen and numerical results are reported using recent potential coefficient determinations. 相似文献
20.
Far-zone effects for different topographic-compensation models based on a spherical harmonic expansion of the topography 总被引:1,自引:1,他引:0
The determination of the gravimetric geoid is based on the magnitude of gravity observed at the surface of the Earth or at
airborne altitude. To apply the Stokes’s or Hotine’s formulae at the geoid, the potential outside the geoid must be harmonic
and the observed gravity must be reduced to the geoid. For this reason, the topographic (and atmospheric) masses outside the
geoid must be “condensed” or “shifted” inside the geoid so that the disturbing gravity potential T fulfills Laplace’s equation everywhere outside the geoid. The gravitational effects of the topographic-compensation masses
can also be used to subtract these high-frequent gravity signals from the airborne observations and to simplify the downward
continuation procedures. The effects of the topographic-compensation masses can be calculated by numerical integration based
on a digital terrain model or by representing the topographic masses by a spherical harmonic expansion. To reduce the computation
time in the former case, the integration over the Earth can be divided into two parts: a spherical cap around the computation
point, called the near zone, and the rest of the world, called the far zone. The latter one can be also represented by a global
spherical harmonic expansion. This can be performed by a Molodenskii-type spectral approach. This article extends the original
approach derived in Novák et al. (J Geod 75(9–10):491–504, 2001), which is restricted to determine the far-zone effects for
Helmert’s second method of condensation for ground gravimetry. Here formulae for the far-zone effects of the global topography
on gravity and geoidal heights for Helmert’s first method of condensation as well as for the Airy-Heiskanen model are presented
and some improvements given. Furthermore, this approach is generalized for determining the far-zone effects at aeroplane altitudes.
Numerical results for a part of the Canadian Rocky Mountains are presented to illustrate the size and distributions of these
effects. 相似文献