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1.
Following a detailed analysis of the weak solution of Neumann and oblique derivative problems [Rozanov and Sansò (1999).
The analysis of the Neumann and the oblique derivative problem. Weak theory], here the so-called regularization theory is
presented. The result, which is already known in mathematical literature, is obtained via a so-called Ladyzenskaya identity,
which is a very interesting tool in itself. The analysis of the stochastic versions of the same problems is tackled and solved.
In so doing, the question of the equivalence between different definitions of generalized random fields is also analyzed.
Received: 1 February 2000 / Accepted: 26 February 2001 相似文献
2.
A new approach for airborne vector gravimetry using GPS/INS 总被引：2，自引：2，他引：2
A new method for airborne vector gravimetry using GPS/INS has been developed and the results are presented. The new algorithm
uses kinematic accelerations as updates instead of positions or velocities, and all calculations are performed in the inertial
frame. Therefore, it is conceptually simpler, easier, more straightforward and computationally less expensive compared to
the traditional approach in which the complex navigation equations should be integrated. Moreover, it is a unified approach
for determining all three vector components, and no stochastic gravity modeling is required. This approach is based on analyzing
the residuals from the Kalman filter of sensor errors, and further processing with wavenumber coefficient filterings is applied
in case closely parallel tracks of data are available. An application to actual test-flight data is performed to test the
validity of the new algorithm. The results yield an accuracy in the down component of about 3–4 mGal. Also, comparable results
are obtained for the horizontal components with accuracies of about 6 mGal. The gravity modeling issue is discussed and alternative
methods are presented, none of which improves on the original approach.
Received: 18 April 2000 / Accepted: 14 August 2000 相似文献
3.
Spatially restricted data distributions on the sphere: the method of orthonormalized functions and applications 总被引：1，自引：0，他引：1
In many geoscientific applications data are irregularly distributed and not globally available, e.g. caps around the poles
which are uncovered due to non-polar satellite orbits, or signals being defined solely on bounded regions on the globe. Starting
from a sequence of base functions with global support, which in the present case is composed of spherical harmonics being
initially non-orthogonal on a bounded subdomain, a set of functions is generated that constitutes an orthonormal basis. Different
approaches to realize this transformation are studied and compared with respect to numerical stability and computational effort,
and the corresponding effects on the coefficient recovery are investigated. A number of synthetic tests demonstrate the applicability,
the benefit, but also the limitations, of this method.
Received: 24 March 2000 / Accepted: 9 October 2000 相似文献
4.
In the framework of a boundary value problem (BVP), when areas on the boundary are void of data the solution of the problem
becomes undetermined and clearly more difficult. Physically, this could be the situation in which a gradiometer on a satellite
on a perfectly circular orbit covers a sphere with measured second radial derivatives: if the satellite orbit is not polar,
there are caps at satellite altitude which are not covered by data. A solution is presented based on an iterative algorithm,
under the hypothesis of using a finite-dimensional model as is usually done in the time-wise approach. The convergence of
the iterative solution is proved and a numerical example is shown to confirm the theoretical result.
Received: 14 August 2000 / Accepted: 12 April 2001 相似文献
5.
We present a spatial decision support system for the non-profit sector, designed to assist planning in the area of home-delivered
services such as meals on wheels. Using data collected from existing programs, current and forecasted demographic data, and
a set of algorithmic tools, we provide a system for evaluating current meals on wheels facilities, and for making incremental
facility location decisions that satisfy coverage and equity requirements.
Received: 27 September 2000 / Accepted: 22 March 2001 相似文献
6.
Gravity recovery using COSMIC GPS data: application of orbital perturbation theory 总被引：14，自引：0，他引：14
C. Hwang 《Journal of Geodesy》2001,75(2-3):117-136
COSMIC is a joint Taiwan–US mission to study the atmosphere using the Global Positioning System (GPS) occultation technique.
Improved formulas are developed for the radial, along-track, and cross-track perturbations, which are more accurate than the
commonly used order-zero formulas. The formulas are used to simulate gravity recovery using the geodetic GPS data of COSMIC
in the operational phase. Results show that the EGM96 model can be improved up to degree 26 using 1 year of COSMIC data. TOPEX/POSEIDON
altimeter data are used to derive a temporal gravity variation. COSMIC cannot reproduce this gravity variation perfectly because
of data noise and orbital configuration, but the recovered field clearly shows the gravity signature due to mass movement
in an El Ni?o.
Received: 3 March 2000 / Accepted: 10 November 2000 相似文献
7.
Multiple Parameter Regularization: Numerical Solutions and Applications to the Determination of Geopotential from Precise Satellite Orbits 总被引：1，自引：0，他引：1
Kaula’s rule of thumb has been used in producing geopotential models from space geodetic measurements, including the most recent models from satellite gravity missions CHAMP. Although Xu and Rummel (Manuscr Geod 20 8–20, 1994b) suggested an alternative regularization method by introducing a number of regularization parameters, no numerical tests have ever been conducted. We have compared four methods of regularization for the determination of geopotential from precise orbits of COSMIC satellites through simulations, which include Kaula’s rule of thumb, one parameter regularization and its iterative version, and multiple parameter regularization. The simulation results show that the four methods can indeed produce good gravitational models from the precise orbits of centimetre level. The three regularization methods perform much better than Kaula’s rule of thumb by a factor of 6.4 on average beyond spherical harmonic degree 5 and by a factor of 10.2 for the spherical harmonic degrees from 8 to 14 in terms of degree variations of root mean squared errors. The maximum componentwise improvement in the root mean squared error can be up to a factor of 60. The simplest version of regularization by multiplying a positive scalar with a unit matrix is sufficient to better determine the geopotential model. Although multiple parameter regularization is theoretically attractive and can indeed eliminate unnecessary regularization for some of the harmonic coefficients, we found that it only improved its one parameter version marginally in this COSMIC example in terms of the mean squared error. 相似文献
8.
Wolf-Dieter Rase 《Journal of Geographical Systems》2001,3(2):199-213
The interpolation of continuous surfaces from discrete points is supported by most GIS software packages. Some packages provide
additional options for the interpolation from 3D line objects, for example surface-specific lines, or contour lines digitized
from topographic maps. Demographic, social and economic data can also be used to construct and display smooth surfaces. The
variables are usually published as sums for polygonal units, such as the number of inhabitants in communities or counties.
In the case of point and line objects the geometric properties have to be maintained in the interpolated surface. For polygon-based
data the geometric properties of the polygon boundary and the volume should be preserved, avoiding redistribution of parts
of the volume to neighboring units during interpolation. The pycnophylactic interpolation method computes a continuous surface
from polygon-based data and simultaneously enforces volume preservation in the polygons. The original procedure using a regular
grid is extended to surface representations based on an irregular triangular network (TIN).
Received: 5 October 2000 / Accepted: 20 December 2000 相似文献
9.
J. Grodecki 《Journal of Geodesy》2001,75(2-3):157-163
A new estimator of variance–covariance components is presented. The proposed estimator is derived by applying the principle
of maximum-likelihood estimation to the posterior probability density function for the case when no prior information is available.
Received: 9 August 1999 / Accepted: 10 November 2000 相似文献
10.
In October 1998 the IGEX field campaign, the first coordinated international effort to monitor GLONASS satellites on global
basis, was started. Currently about 40 institutions worldwide support this effort either by providing GLONASS tracking data
or in operating related data and analysis centers. The increasing quality and consistency of the calculated GLONASS orbits
(about 25 cm early in 2000), even after the end of the official IGEX field campaign, are shown. Particular attention is drawn
to the combination of precise ephemerides in order to generate a robust, reliable and complete IGEX orbits product. Some problems
in modeling the effect of solar radiation pressure on GLONASS satellites are demonstrated. Finally, the expected benefits
and prospects of the upcoming International GLOnass Service-Pilot Project (IGLOS-PP) of the International GPS Service (IGS)
are discussed in more detail.
Received: 17 August 2000 / Accepted: 12 April 2001 相似文献
11.
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
12.
On the basis of the data series of the length of day (LOD), the atmospheric angular momentum (AAM) and the Southern Oscillation
Index (SOI) for January 1970–June 1999, the relationship among Interannual LOD, AAM, and the EL Ni?o/Southern Oscillation
(ENSO) is analyzed by the wavelet transform method. The results suggest that they have similar time-varying spectral structures.
The signals of 1997–98 El Ni?o and 1998–99 La Ni?a events can be detected from the LOD or AAM data.
Received: 25 January 2000 / Accepted: 9 January 2001 相似文献
13.
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
14.
GPS-assisted GLONASS orbit determination 总被引：1，自引：0，他引：1
D. Kuang Y. E. Bar-Sever W. I. Bertiger K. J. Hurst J. F. Zumberge 《Journal of Geodesy》2001,75(11):569-574
Using 1 week of data from a network of GPS/GLONASS dual-tracking receivers, 15-cm accurate GLONASS orbit determination is
demonstrated with an approach that combines GPS and GLONASS data. GPS data are used to define the reference frame, synchronize
receiver clocks and determine troposphere delay for the GLONASS tracking network. GLONASS tracking data are then processed
separately, with the GPS-defined parameters held fixed, to determine the GLONASS orbit. The quality of the GLONASS orbit determination
is currently limited by the size and distribution of the tracking network, and by the unavailability of a sufficiently refined
solar pressure model. Temporal variations in the differential clock bias of the dual-tracking receivers are found to have
secondary impact on the orbit determination accuracy.
Received: 5 January 2000 / Accepted: 15 February 2001 相似文献
15.
Giles M. Foody 《Journal of Geographical Systems》2001,3(3):217-232
Neural networks are attractive tools for the derivation of thematic maps from remotely sensed data. Most attention has focused
on the multilayer perceptron (MLP) network but other network types are available and have different properties that may sometimes
be more appropriate for some applications. Here a MLP, radial basis function (RBF) and probabilistic neural network (PNN)
were used to classify remotely sensed data of an agricultural site. The accuracy of these classifications ranged from 86.25–91.25%.
The accuracy of the PNN classification could be increased through the incorporation of prior probabilities of class membership
but the accuracy of each classification could also be degraded by the presence of an untrained class. Post-classification
analyses, however, could be used to identify potentially misclassified cases, including those belonging to an untrained class,
to increase accuracy. The effect of the post-classification analysis on the accuracy of the classification derived from each
of the three network types investigated differed and it is suggested that network type be selected carefully to meet the requirements
of the application in-hand.
Received: 23 March 2000 / Accepted: 9 July 2000 相似文献
16.
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
17.
Exploring gravity field determination from orbit perturbations of the European Gravity Mission GOCE 总被引：5，自引：0，他引：5
A comparison was made between two methods for gravity field recovery from orbit perturbations that can be derived from global
positioning system satellite-to-satellite tracking observations of the future European gravity field mission GOCE (Gravity
Field and Steady-State Ocean Circulation Explorer). The first method is based on the analytical linear orbit perturbation
theory that leads under certain conditions to a block-diagonal normal matrix for the gravity unknowns, significantly reducing
the required computation time. The second method makes use of numerical integration to derive the observation equations, leading
to a full set of normal equations requiring powerful computer facilities. Simulations were carried out for gravity field recovery
experiments up to spherical harmonic degree and order 80 from 10 days of observation. It was found that the first method leads
to large approximation errors as soon as the maximum degree surpasses the first resonance orders and great care has to be
taken with modeling resonance orbit perturbations, thereby loosing the block-diagonal structure. The second method proved
to be successful, provided a proper division of the data period into orbital arcs that are not too long.
Received: 28 April 2000 / Accepted: 6 November 2000 相似文献
18.
One of the most basic and important tools in optimal spectral gravity field modelling is the method of Wiener filtering.
Originally developed for applications in analogue signal analysis and communication engineering, Wiener filtering has become
a standard linear estimation technique of modern operational geodesy, either as an independent practical tool for data de-noising
in the frequency domain or as an integral component of a more general signal estimation methodology (input–output systems
theory). Its theoretical framework is based on the Wiener–Kolmogorov linear prediction theory for stationary random fields
in the presence of additive external noise, and thus it is closely related to the (more familiar to geodesists) method of
least-squares collocation with random observation errors. The main drawback of Wiener filtering that makes its use in many
geodetic applications problematic stems from the stationarity assumption for both the signal and the noise involved in the
approximation problem. A modified Wiener-type linear estimation filter is introduced that can be used with noisy data obtained
from an arbitrary deterministic field under the masking of non-stationary random observation errors. In addition, the sampling
resolution of the input data is explicitly taken into account within the estimation algorithm, resulting in a resolution-dependent
optimal noise filter. This provides a more insightful approach to spectral filtering techniques for noise reduction, since
the data resolution parameter has not been directly incorporated in previous formulations of frequency-domain estimation problems
for gravity field signals with discrete noisy data.
Received: 1 November 2000 / Accepted: 19 June 2001 相似文献
19.
P. Moore 《Journal of Geodesy》2001,75(5-6):241-254
Dual satellite crossovers (DXO) between the two European Remote Sensing satellites ERS-1 and ERS-2 and TOPEX/Poseidon are
used to (1) refine the Earth's gravity field and (2) extend the study of the ERS-2 altimetric range stability to cover the
first four years of its operation. The enhanced gravity field model, AGM-98, is validated by several methodologies and will
be shown to provide, in particular, low geographically correlated orbital error for ERS-2. For the ERS-2 altimetric range
study, TOPEX/Poseidon is first calibrated through comparison against in situ tide gauge data. A time series of the ERS-2 altimeter
bias has been recovered along with other geophysical correction terms using tables for bias jumps in the range measurements
at the single point target response (SPTR) events. On utilising the original version of the SPTR tables the overall bias drift
is seen to be 2.6±1.0 mm/yr with an RMS of fit of 12.2 mm but with discontinuities at the centimetre level at the SPTR events.
On utilising the recently released revised tables, SPTR2000, the drift is better defined at 2.4±0.6 mm/yr with the RMS of
fit reduced to 3.7 mm. Investigations identify the sea-state bias as a source of error with corrections affecting the overall
drift by close to 1.2 mm/yr.
Received: 25 May 2000 / Accepted: 24 January 2001 相似文献
20.
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