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1.
J. Höpfner 《Journal of Geodesy》2000,74(3-4):335-358
Recently, effective atmospheric-angular-momentum (AAM) functions as calculated from National Centers for Environmental Prediction
(NCEP) (formerly National Meteorological Center, NMC) and National Center for Atmospheric Research (NCAR) Reanalyses have
become available for the years 1958 to 1998. Concerning the wind terms, the top level in the atmosphere used here is 10 hPa.
Compared with earlier NMC model versions, which incorporate wind fields up to 100 hPa since 1976 and up to 50 hPa since 1981,
the reanalyses have produced improved data series over a longer period than before. The axial AAM component χ3 is associated with changes in length of day (LOD). Motivated by better quality and continuity of the series AAM (NCEP) Reanalysis,
the problem of the seasonal imbalances in the solid Earth–atmosphere axial angular momentum budget is re-examined. To assess
better the estimates of the annual and semiannual oscillations in LOD and AAM and of the residual oscillations derived as
difference series between LOD and AAM, the series of LOD data from three analysis centers [International Earth Rotation Service
(IERS), GeoForschungZentrum Potsdam (GFZ) and Jet Propulsion Laboratory Pasadena (JPL)] and of AAM data in terms of χ3(W), χ3(P) and χ3(P+IB) from four meteorological centers [NCEP, Japan Meteorological Agency (JMA), European Centre for Medium-Range Weather
Forecasts (ECMWF) and the UK Meteorological Office (UKMO)] are used in this study. The main analysis steps were removing gaps,
filtering out the seasonal oscillations, calculating optimal estimates of the parameters of the oscillations and calculating
the difference series between the LOD and AAM systems as well as the residuals in the axial angular momentum budget in the
LOD–AAM systems. The results derived as difference series between the different LOD, AAM and LOD–AAM systems show to what
extent the variations reflect systematic differences and significant signals, respectively, which is important for future
activities in this field.
Received: 2 February 1999 / Accepted: 30 November 1999 相似文献
2.
The solutions of the CODE Analysis Center submitted to the IGS, the International Global Position System (GPS) Service for
Geodynamics, are based on three days of observation of about 80–100 stations of the IGS network. The Earth rotation parameters
(ERPs) are assumed to vary linearly over the three days with respect to an a priori model. Continuity at the day boundaries
as well as the continuity of the first derivatives are enforced by constraints. Since early April 1995 CODE has calculated
a new ERP series with an increased time resolution of 2 hours. Again continuity is enforced at the 2-hours-interval boundaries.
The analysis method is described, particularly how to deal with retrograde diurnal terms in the ERP series which may not be estimated with satellite geodetic methods. The results obtained from the first year of data covered by the time series
(time interval from 4 April 1995 to 30 June 1996) are also discussed. The series is relatively homogeneous in the sense of
the used orbit model and the a priori model for the ERPs. The largest source of excitation at daily and sub-daily periods
is likely to be the effect of the ocean tides. There is good agreement between the present results and Topex/Poseidon ocean
tide models, as well as with models based on Very Long Baseline Interferometry (VLBI) and Satellite Laser Ranging (SLR) data.
Non-oceanic periodic variations are also observed in the series. Their origin is most probably a consequence of the GPS solution
strategy; other possible sources are the atmospheric tides.
Received: 13 July 1999 / Accepted: 21 March 2000 相似文献
3.
The Cartesian moments of the mass density of a gravitating body and the spherical harmonic coefficients of its gravitational
field are related in a peculiar way. In particular, the products of inertia can be expressed by the spherical harmonic coefficients
of the gravitational potential as was derived by MacCullagh for a rigid body. Here the MacCullagh formulae are extended to
a deformable body which is restricted to radial symmetry in order to apply the Love–Shida hypothesis. The mass conservation
law allows a representation of the incremental mass density by the respective excitation function. A representation of an
arbitrary Cartesian monome is always possible by sums of solid spherical harmonics multiplied by powers of the radius. Introducing
these representations into the definition of the Cartesian moments, an extension of the MacCullagh formulae is obtained. In
particular, for excitation functions with a vanishing harmonic coefficient of degree zero, the (diagonal) incremental moments
of inertia also can be represented by the excitation coefficients. Four types of excitation functions are considered, namely:
(1) tidal excitation; (2) loading potential; (3) centrifugal potential; and (4) transverse surface stress. One application
of the results could be model computation of the length-of-day variations and polar motion, which depend on the moments of
inertia.
Received: 27 July 1999 / Accepted: 24 May 2000 相似文献
4.
5.
J. Höpfner 《Journal of Geodesy》2001,75(2-3):137-150
The annual and semiannual residuals derived in the axial angular momentum budget of the solid Earth–atmosphere system reflect
significant signals. They must be caused by further excitation sources. Since, in particular, the contribution for the wind
term from the atmospheric layer between the 10 and 0.3 hPa levels to the seasonal variations in length of day (LOD) is still
missing, it is necessary to extend the top level into the upper stratosphere up to 0.3 hPa. Under the conservation of the
total angular momentum of the entire Earth, variations in the oceanic angular momentum (OAM) and the hydrological angular
momentum (HAM) are further significant excitation sources at seasonal time scales. Focusing on other contributions to the
Earth's axial angular momentum budget, the following data are used in this study: axial atmospheric angular momentum (AAM)
data derived for the 10–0.3 hPa layer from 1991 to 1997 for computing the missing wind effects; axial OAM functions as generated
by oceanic general circulation models (GCMs), namely for the ECHAM3 and the MICOM models, available from 1975 to 1994 and
from 1992 to 1994, respectively, for computing the oceanic contributions to LOD changes, and, concerning the HAM variations,
the seasonal estimates of the hydrological contribution as derived by Chao and O'Connor [(1988) Geophys J 94: 263–270]. Using
vector representation, it is shown that the vectors achieve a close balance in the global axial angular momentum budget within
the estimated uncertainties of the momentum quantities on seasonal time scales.
Received: 6 April 2000 / Accepted: 13 December 2000 相似文献
6.
Journal of Geodesy - ?The application of Stokes' formula to create geoid undulations requires no masses outside the geoid. However, due to the existence of the topography, terrain... 相似文献
7.
Length-of-day (LOD) estimates from seven Global Positioning System (GPS) and three satellite laser ranging (SLR) analysis
centers were combined into an even-spaced time series for a 27-month period (1996–1998). This time series was compared to
the multi-technique Earth-orientation-parameter (EOP) combined solution (C04) derived at the Central Bureau of the International
Earth Rotation Service (IERS/CB). Due to inhomogeneities in the different series derived from the various techniques (time,
length, quality, and spatial resolution), the concept of a combined solution is justified. The noise behavior in LOD for different
techniques varies with frequency; the data series were divided into frequency windows after removing both biases and trends.
Different weight factors were assigned in each window, discriminating by technique, and produced one-technique combined solutions.
Finally, these one-technique combined solutions were combined to obtain the final multi-technique solution. The LOD combined
time series obtained by the present method based on the frequency windows combined series (FWCS) is very close to the IERS
C04 solution. It could be useful to generate a new LOD reference time series to be used in the study of high-frequency variations
of Earth rotation.
Received: 28 March 2000 / Accepted: 15 February 2001 相似文献
8.
Considering a GPS satellite and two terrestrial stations, two types of equations are derived relating the heights of the
two stations to the measured data (frequency ratio or clock rate differences) and the coordinates and velocity components
of all three participating objects. The potential possibilities of using such relations for the determination of heights (in
terms of geopotential numbers or orthometric heights) are discussed.
Received: 6 December 2000 / Accepted: 9 July 2001 相似文献
9.
L. E. Sjöberg 《Journal of Geodesy》2002,76(2):115-120
The problems of intersection on the sphere and ellipsoid are studied. On the sphere, the problem of intersection along great
circles is explicitly solved. On the ellipsoid, each of the problems of intersection along arcs of constant azimuth, normal
sections and geodesic lines is solved without any limitation on arc length. In the last case the solution is based on the
Newton–Raphson method of iteration including numerical integration.
Received: 11 April 2001 / Accepted: 3 September 2001 相似文献
10.
A solution to the downward continuation effect on the geoid determined by Stokes' formula 总被引:2,自引:1,他引:2
L.E. Sjöberg 《Journal of Geodesy》2003,77(1-2):94-100
The analytical continuation of the surface gravity anomaly to sea level is a necessary correction in the application of Stokes'
formula for geoid estimation. This process is frequently performed by the inversion of Poisson's integral formula for a sphere.
Unfortunately, this integral equation corresponds to an improperly posed problem, and the solution is both numerically unstable,
unless it is well smoothed, and tedious to compute. A solution that avoids the intermediate step of downward continuation
of the gravity anomaly is presented. Instead the effect on the geoid as provided by Stokes' formula is studied directly. The
practical solution is partly presented in terms of a truncated Taylor series and partly as a truncated series of spherical
harmonics. Some simple numerical estimates show that the solution mostly meets the requests of a 1-cm geoid model, but the
truncation error of the far zone must be studied more precisely for high altitudes of the computation point. In addition,
it should be emphasized that the derived solution is more computer efficient than the detour by Poisson's integral.
Received: 6 February 2002 / Accepted: 18 November 2002
Acknowledgements. Jonas ?gren carried out the numerical calculations and gave some critical and constructive remarks on a draft version of
the paper. This support is cordially acknowledged. Also, the thorough work performed by one unknown reviewer is very much
appreciated. 相似文献
11.
A global plate motion model is established based on the ITRF97 velocity fields and geological model NUVEL1. Sub-plate models
are estimated by using the velocity fields derived from 45 global positioning system (GPS) sites under the ITRF97 reference
frame in China. Comparisons between space geodesy and geological models are given. It is found that the Euler vector of the
AFRC–EURA pair has an obvious discrepancy between space geodetic and geological models. The motion patterns of tectonic blocks
in China predicted by GPS are consistent with those of geological data on the whole.
Received: 9 November 2000 / Accepted: 17 September 2001 相似文献
12.
A synthetic Earth for use in geodesy 总被引:1,自引:0,他引:1
R. Haagmans 《Journal of Geodesy》2000,74(7-8):503-511
A synthetic Earth and its gravity field that can be represented at different resolutions for testing and comparing existing
and new methods used for global gravity-field determination are created. Both the boundary and boundary values of the gravity
potential can be generated. The approach chosen also allows observables to be generated at aircraft flight height or at satellite
altitude. The generation of the synthetic Earth shape (SES) and gravity-field quantities is based upon spherical harmonic
expansions of the isostatically compensated equivalent rock topography and the EGM96 global geopotential model. Spherical
harmonic models are developed for both the synthetic Earth topography (SET) and the synthetic Earth potential (SEP) up to
degree and order 2160 corresponding to a 5′×5′ resolution. Various sets of SET, SES and SEP with boundary geometry and boundary
values at different resolutions can be generated using low-pass filters applied to the expansions. The representation is achieved
in point sets based upon refined triangulation of a octahedral geometry projected onto the chosen reference ellipsoid. The
filter cut-offs relate to the sampling pattern in order to avoid aliasing effects. Examples of the SET and its gravity field
are shown for a resolution with a Nyquist sampling rate of 8.27 degrees.
Received: 6 August 1999 / Accepted: 26 April 2000 相似文献
13.
This paper generalizes the Stokes formula from the spherical boundary surface to the ellipsoidal boundary surface. The resulting
solution (ellipsoidal geoidal height), consisting of two parts, i.e. the spherical geoidal height N
0 evaluated from Stokes's formula and the ellipsoidal correction N
1, makes the relative geoidal height error decrease from O(e
2) to O(e
4), which can be neglected for most practical purposes. The ellipsoidal correction N
1 is expressed as a sum of an integral about the spherical geoidal height N
0 and a simple analytical function of N
0 and the first three geopotential coefficients. The kernel function in the integral has the same degree of singularity at
the origin as the original Stokes function. A brief comparison among this and other solutions shows that this solution is
more effective than the solutions of Molodensky et al. and Moritz and, when the evaluation of the ellipsoidal correction N
1 is done in an area where the spherical geoidal height N
0 has already been evaluated, it is also more effective than the solution of Martinec and Grafarend.
Received: 27 January 1999 / Accepted: 4 October 1999 相似文献
14.
The identification of mean semi-major axes (suitably defined) for satellite orbits to satisfy a variety of requirements for
geodesy, geophysics and oceanography, in terms of repeat orbits (with orbital resonances), is investigated. Various options
for the definition of semi-major axis, from the viewpoint of satellite dynamics, are described. Simple simulations of the
expected resonant changes in inclination are presented, and tools for the analysis of orbit resonances to extract certain
lumped harmonic coefficients of the geopotential (e.g. from the very precise CHAMP orbit) are resurrected. Finally, a preliminary
example of the 46th-order resonance analysis possible for CHAMP, based on the mean orbital elements produced by GFZ (GeoForschungs
Zentrum) for ephemeris prediction, is presented.
Received: 10 July 2001 / Accepted: 17 July 2002
Correspondence to: J. Klokočník at Ondřejov Observatory
Acknowledgements. We thank Prof. Dr. Ch. Reigber, Dr. P. Schwintzer, Dr. T. Gruber and Dr. R. K?nig from GFZ Potsdam for various consultations
and discussions, and for the CHAMP two-line mean elements. This investigation was performed under the aegis of CEDR (Center
for Earth's Dynamics Research, Prague-Ondřejov); it has been supported by project LN00A005 (provided by the Ministry of Education
of the Czech Republic) and by grant A 3004 of the Grant Agency of the Academy of Sciences of the Czech Republic. 相似文献
15.
C. Vigny J. Chéry T. Duquesnoy F. Jouanne J. Ammann M. Anzidei J.-P. Avouac F. Barlier R. Bayer P. Briole E. Calais F. Cotton F. Duquenne K. L. Feigl G. Ferhat M. Flouzat J.-F. Gamond A. Geiger A. Harmel M. Kasser M. Laplanche M. Le Pape J. Martinod G. Ménard B. Meyer J.-C. Ruegg J.-M. Scheubel O. Scotti G. Vidal 《Journal of Geodesy》2002,76(2):63-76
The Western Alps are among the best studied collisional belts with both detailed structural mapping and also crustal geophysical
investigations such as the ECORS and EGT seismic profile. By contrast, the present-day kinematics of the belt is still largely
unknown due to small relative motions and the insufficient accuracy of the triangulation data. As a consequence, several tectonic
problems still remain to be solved, such as the amount of N–S convergence in the Occidental Alps, the repartition of the deformation
between the Alpine tectonic units, and the relation between deformation and rotation across the Alpine arc. In order to address
these problems, the GPS ALPES group, made up of French, Swiss and Italian research organizations, has achieved the first large-scale
GPS surveys of the Western Alps. More than 60 sites were surveyed in 1993 and 1998 with a minimum observation of 3 days at
each site. GPS data processing has been done by three independent teams using different software. The different solutions
have horizontal repeatabilities (N–E) of 4–7 mm in 1993 and 2–3 mm in 1998 and compare at the 3–5-mm level in position and
2-mm/yr level in velocity. A comparison of 1993 and 1998 coordinates shows that residual velocities of the GPS marks are generally
smaller than 2 mm/yr, precluding a detailed tectonic interpretation of the differential motions. However, these data seem
to suggest that the N–S compression of the Western Alps is quite mild (less than 2 mm/yr) compared to the global convergence
between the African and Eurasian plate (6 mm/yr). This implies that the shortening must be accomodated elsewhere by the deformation
of the Maghrebids and/or by rotations of Mediterranean microplates. Also, E–W velocity components analysis supports the idea
that E–W extension exists, as already suggested by recent structural and seismotectonic data interpretation.
Received: 27 November 2000 / Accepted: 17 September 2001 相似文献
16.
P. J. G. Teunissen 《Journal of Geodesy》2001,75(7-8):399-407
Carrier phase ambiguity resolution is the key to fast and high-precision GNSS (Global Navigation Satellite System) kinematic
positioning. Critical in the application of ambiguity resolution is the quality of the computed integer ambiguities. Unsuccessful
ambiguity resolution, when passed unnoticed, will too often lead to unacceptable errors in the positioning results. Very high
success rates are therefore required for ambiguity resolution to be reliable. Biases which are unaccounted for will lower
the success rate and thus increase the chance of unsuccessful ambiguity resolution. The performance of integer ambiguity estimation
in the presence of such biases is studied. Particular attention is given to integer rounding, integer bootstrapping and integer
least squares. Lower and upper bounds, as well as an exact and easy-to-compute formula for the bias-affected success rate,
are presented. These results will enable the evaluation of the bias robustness of ambiguity resolution.
Received: 28 September 2000 / Accepted: 29 March 2001 相似文献
17.
A potential-type Molodensky telluroid based upon a minimum-distance mapping is derived. With respect to a reference potential
of Somigliana–Pizzetti type which relates to the World Geodetic Datum 2000, it is shown that a point-wise minimum-distance
mapping of the topographical surface of the Earth onto the telluroid surface, constrained to the gauge W(P)=u(p), leads to a system of four nonlinear normal equations. These normal equations are solved by a fast Newton–Raphson iteration.
Received: 7 February 2000 / Accepted: 23 October 2001 相似文献
18.
L. E. Sjöberg 《Journal of Geodesy》2001,75(5-6):283-290
The topographic and atmospheric effects of gravimetric geoid determination by the modified Stokes formula, which combines
terrestrial gravity and a global geopotential model, are presented. Special emphasis is given to the zero- and first-degree
effects. The normal potential is defined in the traditional way, such that the disturbing potential in the exterior of the
masses contains no zero- and first-degree harmonics. In contrast, it is shown that, as a result of the topographic masses,
the gravimetric geoid includes such harmonics of the order of several centimetres. In addition, the atmosphere contributes
with a zero-degree harmonic of magnitude within 1 cm.
Received: 5 November 1999 / Accepted: 22 January 2001 相似文献
19.
Local geoid determination combining gravity disturbances and GPS/levelling: a case study in the Lake Nasser area, Aswan, Egypt 总被引:1,自引:0,他引:1
C. C. Tscherning Awar Radwan A. A. Tealeb S. M. Mahmoud M. Abd El-Monum Ramdan Hassan I. El-Syaed K. Saker 《Journal of Geodesy》2001,75(7-8):343-348
The use of GPS for height control in an area with existing levelling data requires the determination of a local geoid and
the bias between the local levelling datum and the one implicitly defined when computing the local geoid. If only scarse gravity
data are available, the heights of new data may be collected rapidly by determining the ellipsoidal height by GPS and not
using orthometric heights. Hence the geoid determination has to be based on gravity disturbances contingently combined with
gravity anomalies. Furthermore, existing GPS/levelling data may also be used in the geoid determination if a suitable general
gravity field modelling method (such as least-squares collocation, LSC) is applied. A comparison has been made in the Aswan
Dam area between geoids determined using fast Fourier transform (FFT) with gravity disturbances exclusively and LSC using
only the gravity disturbances and the disturbances combined with GPS/levelling data. The EGM96 spherical harmonic model was
in all cases used in a remove–restore mode. A total of 198 gravity disturbances spaced approximately 3 km apart were used,
as well as 35 GPS/levelling points in the vicinity and on the Aswan Dam. No data on the Nasser Lake were available. This gave
difficulties when using FFT, which requires the use of gridded data. When using exclusively the gravity disturbances, the
agreement between the GPS/levelling data were 0.71 ± 0.17 m for FFT and 0.63 ± 0.15 for LSC. When combining gravity disturbances
and GPS/levelling, the LSC error estimate was ±0.10 m. In the latter case two bias parameters had to be introduced to account
for a possible levelling datum difference between the levelling on the dam and that on the adjacent roads.
Received: 14 August 2000 / Accepted: 28 February 2001 相似文献
20.
Simplified formulae for the BIQUE estimation of variance components in disjunctive observation groups 总被引:7,自引:1,他引:6
General rigorous and simplified formulae are reported for the best invariant quadratic unbiased estimates of the variance–covariance
components, which can be applied to all least-squares adjustments with the general linear stochastic model. Simplified procedures
are given for two cases frequently recurring in geodetic applications: uncorrelated groups of correlated or uncorrelated observations,
with more than one variance component in each group.
Received: 19 November 1998 / Accepted: 21 March 2000 相似文献