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1.
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
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.
Five separate polar motion series are examined in order to understand what portion of their variations at periods exceeding
several years represents true polar motion. The data since the development of space-geodetic techniques (by themselves insufficient
for study of long-period motion), and a variety of historical astrometric data sets, allow the following tentative conclusions:
retrograde long-period polar motion below about −0.2 cpy (cycles per year) in pre-space-geodetic data (pre-1976) is dominantly
noise. For 1976–1992, there is poor agreement between space-geodetic and astrometric series over the range −0.2 to +0.2 cpy,
demonstrating that classical astrometry lacked the precision to monitor polar motion in this frequency range. It is concluded
that all the pre-1976 astrometric polar motion data are likely to be dominated by noise at periods exceeding about 10 years.
The exception to this is possibly a linear trend found in some astrometric and space geodetic series. At frequencies above
prograde +0.2 cpy (periods shorter than about 5 years), historical astrometric data may be of sufficient quality for comparisons
with geophysical excitation time series. Even in the era of space geodesy, significant differences are found in long-period
variations in published polar motion time series.
Received: 27 March 2001 / Accepted: 15 October 2001 相似文献
4.
The short-term prediction of Earth rotation parameters (ERP) (length-of-day and polar motion) is studied up to 10 days by means of ANFIS (adaptive network based fuzzy inference system). The prediction is then extended to 40 days into the future by using the formerly predicted values as input data. The ERP C04 time series with daily values from the International Earth Rotation Service (IERS) serve as the data base. Well-known effects in the ERP series, such as the impact of the tides of the solid Earth and the oceans or seasonal variations of the atmosphere, were removed a priori from the C04 series. The residual series were used for both training and validation of the network. Different network architectures are discussed and compared in order to optimize the network solution. The results of the prediction are analyzed and compared with those of other methods. Short-term ERP values predicted by ANFIS show root-mean-square errors which are equal to or even lower than those from the other considered methods. The presented method is easy to use.Acknowledgments. The presented study was undertaken during a six-month stay of the first author at the DGFI (Deutsches Geodätisches Forschungsinstitut) in Munich. The authors wish to thank the DAAD (German Academic Exchange Service) for its support of this project. The first author would like to express many thanks to Prof. Dr.-Ing. Hermann Drewes and all other administrative and academic staff at the DGFI for providing a very warm welcome which motivated and encouraged him during his study on this project. The cooperation of Dr.-Ing. Katja Heine (TU Cottbus, Germany) is gratefully acknowledged, in particular her hospitality during the two stays of the first author in Cottbus. 相似文献
5.
P. H. Andersen 《Journal of Geodesy》2000,74(7-8):531-551
The method of square root information filtering and smoothing (SRIF/S) is reviewed and has been implemented in the combined
square root information filter and smoother (CSRIFS) program. CSRIFS is a part of the GEOSAT space geodesy software developed
at Forsvarets forskningsinstitutt (FFI, The Norwegian Defence Research Establishment). The state vectors and complete variance–covariance
matrices from the analyses of a number of independent arcs of space geodesy data can be combined using CSRIFS. Four parameter
levels are available and any parameter can, at each level, be represented as either a constant or a stochastic parameter (white
noise, colored noise, or random walk). The batch length (i.e. the time interval between the addition of noise to the SRIF
array) can be made time and parameter dependent. CSRIFS was applied in the combination of 623 very long baseline interferometry
(VLBI) observing sessions. The purpose of this test was to validate the computer implementation of the SRIF/S method and to
give an example of how this method can be used in the analysis of a large number of space geodetic observations. The results
show that the implementation is very satisfactory.
Received: 28 May 1999 / Accepted: 15 June 2000 相似文献
6.
G. Even-Tzur 《Journal of Geodesy》2002,76(8):455-461
The performance of geodetic monitoring networks is heavily influenced by the configuration of the measured GPS vectors. As
an effective design of the GPS measurements will decrease GPS campaign costs and increase the accuracy and reliability of
the entire network, the identification of the preferred GPS vectors for measurement has been highlighted as a core problem
in the process of deformation monitoring. An algorithm based on a sensitivity analysis of the network, as dependent upon a
postulated velocity field, is suggested for the selection of the optimal GPS vectors. Relevant mathematical and statistical
concepts are presented as the basis for an improved method of vector configuration design. A sensitivity analysis of the geodetic
geodynamic network in the north of Israel is presented, where the method is examined against two deformation models, the Simple
Transform Fault and the Locked Fault. The proposed method is suggested as a means for the improvement of the design of monitoring
networks, a common practice worldwide.
Received: 30 July 2001 / Accepted: 3 June 2002
Acknowledgments. It is my pleasant duty to thank the Survey of Israel and Dr. E. Ostrovsky for providing the variance–covariance matrix of
the G1 network in northern Israel. I would like to thank the reviewers of this paper for their constructive and helpful remarks. 相似文献
7.
J. Marshall 《Journal of Geodesy》2002,76(6-7):334-344
Several pre-analysis measures which help to expose the behavior of L
1 -norm minimization solutions are described. The pre-analysis measures are primarily based on familiar elements of the linear
programming solution to L
1-norm minimization, such as slack variables and the reduced-cost vector. By examining certain elements of the linear programming
solution in a probabilistic light, it is possible to derive the cumulative distribution function (CDF) associated with univariate
L
1-norm residuals. Unlike traditional least squares (LS) residual CDFs, it is found that L
1-norm residual CDFs fail to follow the normal distribution in general, and instead are characterized by both discrete and
continuous (i.e. piecewise) segments. It is also found that an L
1 equivalent to LS redundancy numbers exists and that these L
1 equivalents are a byproduct of the univariate L
1 univariate residual CDF. Probing deeper into the linear programming solution, it is found that certain combinations of observations
which are capable of tolerating large-magnitude gross errors can be predicted by comprehensively tabulating the signs of slack
variables associated with the L
1 residuals. The developed techniques are illustrated on a two-dimensional trilateration network.
Received: 6 July 2001 / Accepted: 21 February 2002 相似文献
8.
Prediction of surface horizontal displacements, and gravity and tilt changes caused by filling the Three Gorges Reservoir 总被引:11,自引:0,他引:11
Horizontal displacements, and gravity and tilt changes induced by filling the Three Gorges Reservoir are modeled using elastic
loading Green functions. When the water surface reaches its highest level, the effects become maximum on the reservoir banks.
The longitudinal and latitudinal components of the horizontal displacements reach −8.2 and 7.7 mm respectively, gravity is
increased by up to 3.4 mGal, and the prime vertical and meridian components of the tilt changes are −7.8 and −17.5 arcseconds
respectively. Accordingly, the filling of the reservoir will influence values observed from global positioning system (GPS),
gravimetry and tilt measurements in the area. The results given can be used to provide important corrections for extracting
earthquake-related signals from observed data.
Received: 19 January 2001 / Accepted: 3 September 2001 相似文献
9.
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
10.
Possible improvement of Earth orientation forecast using autocovariance prediction procedures 总被引:1,自引:2,他引:1
Autocovariance prediction has been applied to attempt to improve polar motion and UT1-UTC predictions. The predicted polar
motion is the sum of the least-squares extrapolation model based on the Chandler circle, annual and semiannual ellipses, and
a bias fit to the past 3 years of observations and the autocovariance prediction of these extrapolation residuals computed
after subtraction of this model from pole coordinate data. This prediction method has been applied also to the UT1-UTC data,
from which all known predictable effects were removed, but the prediction error has not been reduced with respect to the error
of the current prediction model. However, the results show the possibility of decreasing polar motion prediction errors by
about 50 for different prediction lengths from 50 to 200 days with respect to the errors of the current prediction model.
Because of irregular variations in polar motion and UT1-UTC, the accuracy of the autocovariance prediction does depend on
the epoch of the prediction. To explain irregular variations in x, y pole coordinate data, time-variable spectra of the equatorial components of the effective atmospheric angular momentum, determined
by the National Center for Environmental Prediction, were computed. These time-variable spectra maxima for oscillations with
periods of 100–140 days, which occurred in 1985, 1988, and 1990 could be responsible for excitation of the irregular short-period
variations in pole coordinate data. Additionally, time-variable coherence between geodetic and atmospheric excitation function
was computed, and the coherence maxima coincide also with the greatest irregular variations in polar motion extrapolation
residuals.
Received: 22 October 1996 / Accepted: 16 September 1997 相似文献
11.
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
12.
Eduardo Eiji Maeda Antonio Roberto Formaggio Yosio Edemir Shimabukuro Gustavo Felipe Balué Arcoverde Matthew C. Hansen 《International Journal of Applied Earth Observation and Geoinformation》2009
The presented work describes a methodology that employs artificial neural networks (ANN) and multi-temporal imagery from the MODIS/Terra-Aqua sensors to detect areas of high risk of forest fire in the Brazilian Amazon. The hypothesis of this work is that due to characteristic land use and land cover change dynamics in the Amazon forest, forest areas likely to be burned can be separated from other land targets. A study case was carried out in three municipalities located in northern Mato Grosso State, Brazilian Amazon. Feedforward ANNs, with different architectures, were trained with a backpropagation algorithm, taking as inputs the NDVI values calculated from MODIS imagery acquired during five different periods preceding the 2005 fire season. Selected samples were extracted from areas where forest fires were detected in 2005 and from other non-burned forest and agricultural areas. These samples were used to train, validate and test the ANN. The results achieved a mean squared error of 0.07. In addition, the model was simulated for an entire municipality and its results were compared with hotspots detected by the MODIS sensor during the year. A histogram analysis showed that the spatial distribution of the areas with fire risk were consistent with the fire events observed from June to December 2005. The ANN model allowed a fast and relatively precise method to predict forest fire events in the studied area. Hence, it offers an excellent alternative for supporting forest fire prevention policies, and in assisting the assessment of burned areas, reducing the uncertainty involved in currently used methods. 相似文献
13.
ITRS, PZ-90 and WGS 84: current realizations and the related transformation parameters 总被引:4,自引:0,他引:4
The first results of the International GLONASS Experiment 1998 (IGEX-98) campaign have provided significant material to illustrate
the mutual benefits of the GLONASS system and the realization of the International Terrestrial Reference System (ITRS). A
specific aspect, namely the relationship between the World Geodetic System 1984 (WGS 84) and the PZ-90 system using ITRS as
a primary standard, is investigated. A review of current works is carried out. A transformation strategy is proposed for the
three systems based on recent results from IGEX-98 and an independent set of transformation parameters derived by the Jet
Propulsion Laboratory from ITRF97 and PZ-90 coordinates for 16 global stations.
Received: 9 June 2000 / Accepted: 12 June 2001 相似文献
14.
Laser-based validation of GLONASS orbits by short-arc technique 总被引:1,自引:0,他引:1
F. Barlier C. Berger P. Bonnefond P. Exertier O. Laurain J. F. Mangin J. M. Torre 《Journal of Geodesy》2001,75(11):600-612
The International GLONASS Experiment (IGEX-98) was carried out between 19 October 1998 and 19 April 1999. Among several objectives
was the precise orbit determination of GPS and GLONASS satellites and its validation by laser ranging observations. Local
laser-based orbit corrections (radial, tangential and normal components in a rotating orbital local reference frame) are computed
using a geometrical short-arc technique. The order of magnitude of these corrections is at the level of few decimeters, depending
on the considered components. The orbit corrections are analyzed as a function of several parameters (date, orbital plane,
geographical area). The mean corrections are at the level of several centimeters. However, when averaging over the entire
campaign and for all the satellites, no mean radial, tangential and normal orbit corrections are found. The origin of the
observed corrections is considered (errors due to the geocentric gravitational constant, the non-gravitational forces, the
thermal equilibrium of on-board equipment, the reference systems, the location and the signature of the retroreflector array,
and the precision of the satellite laser ranges). Some features are also due to errors in the radio-tracking GLONASS orbits.
Further investigations will be needed to better understand the origin of various biases.
Received: 17 February 2000 / Accepted: 31 January 2001 相似文献
15.
R. S. Gross 《Journal of Geodesy》2000,73(12):627-637
Independent Earth-orientation measurements taken by the space-geodetic techniques of lunar and satellite laser ranging, very-long-baseline
interferometry, and the global positioning system have been combined using a Kalman filter. The resulting combined Earth-orientation
series, SPACE97, consists of values and uncertainties for universal time, polar motion, and their rates spanning the period
28 September 1976 to 3 January 1998 at daily intervals. The space-geodetic measurements used to generate SPACE97 have then
been combined with optical astrometric measurements to form two additional combined Earth-orientation series: (1) COMB97,
consisting of values and uncertainties for universal time, polar motion, and their rates spanning the period 20 January 1962
to 1 January 1998 at 5-day intervals, and (2) POLE97, consisting of values and uncertainties for polar motion and its rate
spanning the period 20 January 1900 to 21 December 1997 at monthly intervals.
Received: 10 August 1998 / Accepted: 31 May 1999 相似文献
16.
The New Hebrides experiment consisted of setting up a pair of DORIS beacons in remote tropical islands in the southwestern
Pacific, between 1993 and 1997. Because of orbitography requirements on TOPEX/Poséidon, the beacons were only transmitting
to SPOT satellites. Root-mean-square (RMS) scatters at the centimeter level on the latitude and vertical components were achieved,
but 2-cm RMS scatters affected the longitude component. Nevertheless, results of relative velocity (123 mm/year N250°) are
very consistent with those obtained using the global positioning system (GPS) (126 mm/yr N246°). The co-seismic step (12 mm
N60°) related to the Walpole event (M
W = 7.7) is consistent with that derived from GPS (10 mm N30°) or from the centroid moment tensor (CMT) of the quake (12 mm
N000°).
Received: 19 November 1999 / Accepted: 17 May 2000 相似文献
17.
Regularization of geopotential determination from satellite data by variance components 总被引:11,自引:18,他引:11
Different types of present or future satellite data have to be combined by applying appropriate weighting for the determination
of the gravity field of the Earth, for instance GPS observations for CHAMP with satellite to satellite tracking for the coming
mission GRACE as well as gradiometer measurements for GOCE. In addition, the estimate of the geopotential has to be smoothed
or regularized because of the inversion problem. It is proposed to solve these two tasks by Bayesian inference on variance
components. The estimates of the variance components are computed by a stochastic estimator of the traces of matrices connected
with the inverse of the matrix of normal equations, thus leading to a new method for determining variance components for large
linear systems. The posterior density function for the variance components, weighting factors and regularization parameters
are given in order to compute the confidence intervals for these quantities. Test computations with simulated gradiometer
observations for GOCE and satellite to satellite tracking for GRACE show the validity of the approach.
Received: 5 June 2001 / Accepted: 28 November 2001 相似文献
18.
Z. Malkin 《Journal of Geodesy》2009,83(6):547-556
In this paper, a new geometry index of very long baseline interferometry (VLBI) observing networks, the volume of network
V, is examined as an indicator of the errors in the Earth orientation parameters (EOP) obtained from VLBI observations. It
has been shown that both EOP precision and accuracy can be well described by the power law σ = aV
c
in a wide range of the network size from domestic to global VLBI networks. In other words, as the network volume grows, the
EOP errors become smaller following a power law. This should be taken into account for a proper comparison of EOP estimates
obtained from different VLBI networks. Thus, performing correct EOP comparison allows us to investigate accurately finer factors
affecting the EOP errors. In particular, it was found that the dependence of the EOP precision and accuracy on the recording
data rate can also be described by a power law. One important conclusion is that the EOP accuracy depends primarily on the
network geometry and to lesser extent on other factors, such as recording mode and data rate and scheduling parameters, whereas
these factors have a stronger impact on the EOP precision. 相似文献
19.
The single- and dual-satellite crossover (SSC and DSC) residuals between and among Geosat, TOPEX/Poseidon (T/P), and ERS
1 or 2 have been used for various purposes, applied in geodesy for gravity field accuracy assessments and determination as
well as in oceanography. The theory is presented and various examples are given of certain combinations of SSC and DSC that test for residual altimetry data errors, mostly of non-gravitational origin, of the order of a few centimeters.
There are four types of basic DSCs and 12 independent combinations of them in pairs which have been found useful in the present
work. These are defined in terms of the `mean' and `variable' components of a satellite's geopotential orbit error from Rosborough's
1st-order analytical theory. The remaining small errors, after all altimeter data corrections are applied and the relative
offset of coordinate frames between altimetry missions removed, are statistically evaluated by means of the Student distribution.
The remaining signal of `non-gravitational' origin can in some cases be attributed to the main ocean currents which were not
accounted for among the media or sea-surface corrections. In future, they may be resolved by a long-term global circulation
model. Experience with two current models, neither of which are found either to cover the most critical missions (Geosat &
TOPEX/Poseidon) or to have the accuracy and resolution necessary to account for the strongest anomalies found across them,
is described. In other cases, the residual signal is due to errors in tides, altimeter delay corrections or El Ni?o. (Various
examples of these are also presented.) Tests of the combinations of the JGM 3-based DSC residuals show that overall the long-term
data now available are well suited for a gravity field inversion refining JGM 3 for low- and resonant-order geopotential harmonics
whose signatures are clearly seen in the basic DSC and SSC sets.
Received: 15 January 1999 / Accepted: 9 September 1999 相似文献
20.
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