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1.
An adaptive finite-duration impulse response filter, based on a least-mean-square algorithm, has been used to mitigate multipath
effects, and to derive tectonic and fault movement signals from continuous global positioning system (CGPS) data. By applying
the filter on both pseudo-range and carrier-phase multipath sequences from CGPS observations on consecutive days, multipath
models have been reliably derived. The standard deviations of residual time series are reduced to about one-quarter on pseudo-range
and to about one-half on carrier phase. The adaptive filter is then used to process baseline solutions from a five-station
array. Tectonic and fault movements have been resolved, which are in good agreement with previous studies involving many more
CGPS stations.
Received: 11 February 2000 / Accepted: 28 June 2000 相似文献
2.
The method of Bjerhammar is studied in the continuous case for a sphere. By varying the kernel function, different types of
unknowns (u *) are obtained at the internal sphere (the Bjerhammar sphere). It is shown that a necessary condition for the existence of
u * is that the degree variances (σ
n
2
) of the observations are of an order less than n −2. According to Kaula’s rule this condition is not satisfied for the earth’s gravity anomaly field (σ
n
2
=n −1) but well for the geopotential (σ
n
2
=n −3). 相似文献
3.
We propose a spatial error model with continuous random effects based on Matérn covariance functions and apply this model for the analysis of income convergence processes ( \(\beta \)-convergence). The use of a model with continuous random effects permits a clearer visualization and interpretation of the spatial dependency patterns, avoids the problems of defining neighborhoods in spatial econometrics models, and allows projecting the spatial effects for every possible location in the continuous space, circumventing the existing aggregations in discrete lattice representations. We apply this model approach to analyze the economic growth of Brazilian municipalities between 1991 and 2010 using unconditional and conditional formulations and a spatiotemporal model of convergence. The results indicate that the estimated spatial random effects are consistent with the existence of income convergence clubs for Brazilian municipalities in this period. 相似文献
4.
The standard analytical approach which is applied for constructing geopotential models OSU86 and earlier ones, is based on
reducing the boundary value equation to a sphere enveloping the Earth and then solving it directly with respect to the potential
coefficients
n,m
. In an alternative procedure, developed by Jekeli and used for constructing the models OSU91 and EGM96, at first an ellipsoidal
harmonic series is developed for the geopotential and then its coefficients
n,m
e
are transformed to the unknown
n,m
. The second solution is more exact, but much more complicated. The standard procedure is modified and a new simple integral
formula is derived for evaluating the potential coefficients. The efficiency of the standard and new procedures is studied
numerically. In these solutions the same input data are used as for constructing high-degree parts of the EGM96 models. From
two sets of
n,m
( n≤360,| m|≤ n), derived by the standard and new approaches, different spectral characteristics of the gravity anomaly and the geoid undulation
are estimated and then compared with similar characteristics evaluated by Jekeli's approach (`etalon' solution). The new solution
appears to be very close to Jekeli's, as opposed to the standard solution. The discrepancies between all the characteristics
of the new and `etalon' solutions are smaller than the corresponding discrepancies between two versions of the final geopotential
model EGM96, one of them (HDM190) constructed by the block-diagonal least squares (LS) adjustment and the other one (V068)
by using Jekeli's approach. On the basis of the derived analytical solution a new simple mathematical model is developed to
apply the LS technique for evaluating geopotential coefficients.
Received: 12 December 2000 / Accepted: 21 June 2001 相似文献
5.
The study compared forest cover maps derived using coarse resolution vegetation continuous fields (MODIS VCF; 500m resolution)
with the maps derived from medium resolution (24m; IRS LISS-III) data. The comparison of VCF, per cent tree cover product,
for the years 2000 to 2004 with LISS III forest density class maps of 2001 and 2003 was carried out for two sites representing
hilly (Uttarakhand) and undulating terrains (Madhya Pradesh). Slicing VCF to corresponding forest crown cover, i.e., 0–10%,
10–40%, 40–70% and >70% produced considerable difference in forest area estimates when compared to original LISS III derived
crown cover area. The corresponding value range in VCF for 0–10% of actual forest cover were 0–31% and 0–25% in 2 sites respectively,
and the respective limit was consistent at 1–20% when VCF range were sliced with respect to upscaled LISS III at 500m resolution.
Similarly, all other class limits were also found through iterative process. These limits were similar, within a site, across
five years. Spatial Kappa match between these two data indicated higher match in 40–70% class, and also in undulating site.
When compared at same resolution, similar forest area cover estimated with weighted area upscaling gave closest match. The
study is useful in knowing the usability and limits of VCF product, and utility of spatial Kappa. 相似文献
6.
In this paper we propose a continuous spatio-temporal model that describes population change in a region in terms of population growth, migration drift towards regions with better economic or climate conditions, and population diffusion from more populated to less populated areas. Finite-differences are used to approximate the space and time derivatives. The model is estimated by using population data from the US census corresponding to the period 1790–1910. People tend to migrate from east to west, and to relocate towards regions with lower precipitation levels and more abundant coal and iron resources. Also population growth tends to be larger in zones with higher precipitation levels and higher temperatures. 相似文献
7.
Three-dimensional ocean tide loading (OTL) displacements of eight diurnal and semidiurnal constituents at 12 sites in Hong
Kong were estimated using 3–7 years of continuous global positioning system (GPS) observations. OTL displacements were estimated
using the precise point positioning (PPP) technique on a daily basis and then combined. The OTL displacements obtained by
GPS were compared with predictions using seven recent global ocean tide models. The effect of OTL displacements on GPS position
time series was also investigated. The study shows that the GPS-derived OTL displacements (excluding K1 and K2 constituents)
agree best with those predicted by the GOT4.7 and NAO99b models. The GPS/model agreement is generally at the sub-millimeter
level, except for S2, K1, and K2 constituents with relatively large errors. After systematic biases between the GPS and model
values are removed, the misfits of all sites for M2, S2, N2, O1, P1, and Q1 are less than 0.5 and 1.0 mm in the horizontal
and vertical components, respectively, while larger misfits (within 2.5 mm) are observed for K1 and K2. Integer ambiguity
fixing slightly improves the east component of OTL displacement estimates. The study also finds that GPS-derived OTL corrections,
instead of model predicts, can be used in daily data processing with the exception of K1 and K2. Including K2 corrections,
a secular vertical rate of up to 1 mm/year in position time series can be induced, which needs to be confirmed by further
studies. 相似文献
8.
In this paper, we extend the Bayesian methodology introduced by Beamonte et al. (Stat Modelling 8:285–311, 2008) for the estimation and comparison of spatio-temporal autoregressive models (STAR) with neighbourhood effects, providing
a more general treatment that uses larger and denser nets for the number of spatial and temporal influential neighbours and
continuous distributions for their smoothing weights. This new treatment also reduces the computational time and the RAM necessities
of the estimation algorithm in Beamonte et al. (Stat Modelling 8:285–311, 2008). The procedure is illustrated by an application to the Zaragoza (Spain) real estate market, improving the goodness of fit
and the outsampling behaviour of the model thanks to a more flexible estimation of the neighbourhood parameters. 相似文献
9.
None of the currently developed activity-based models of transport demand explicitly models task allocation among household
members. To fill this gap, the present paper suggests to complement activity-based models of activity scheduling with a context-dependent
model of task allocation. That is, it is assumed that the allocation of tasks within households is partly based on such contextual
variables as the amount of time a member has to spend on mandatory activities and car availability. In particular, the paper
advocates a conjoint-based approach, based on an assignment task as opposed to the traditional ranking, rating or choice response
formats. By definition, an assignment task involves a combinatorial explosion of choice alternatives, implying that additional
operational decisions to estimate the context-dependent model are required. This study presents the results of various numerical
experiments, conducted to better understand the impacts of those decisions on the degree of bias in the parameter estimates
of the choice model. The results of these simulations indicate that under particular assumptions, the development and estimation
of a conjoint-based, context-dependent model of task allocation within households is feasible.
Received: March 1999 / Accepted: June 2001 相似文献
11.
The second Baltic Sea Level (BSL) GPS campaign was run for one week in June 1993. Data from 35 tide gauge sites and five
fiducial stations were analysed, for three fiducial stations (Onsala, Mets?hovi and Wettzell) fixed at the ITRF93 system.
On a time-scale of 5 days, precision was several parts in 10 9 for the horizontal and vertical components. Accuracies were about 1 cm in comparison with the International GPS Geodynamical
Service (IGS) coordinates in three directions. To connect the Swedish and the Finnish height systems, our numerical application
utilises three approaches: a rigorous approach, a bias fit and a three-parameter fit. The results between the Swedish RH70
and the Finnish N 60 systems are estimated to −19.3 ± 6.5, −17 ± 6 and −15 ± 6 cm, respectively, by the three approaches.
The results of the three indirect methods are in an agreement with those of a direct approach from levelling and gravity measurements.
Received: 3 April 1996 / Accepted: 4 August 1997 相似文献
12.
A new method for calculating analytical solar radiation pressure models for GNSS spacecraft has been developed. The method
simulates the flux of light from the Sun using a pixel array. The method can cope with a high level of complexity in the spacecraft
structure and models effects due to reflected light. Models have been calculated and tested for the Russhar global navigation
satellite system GLONASS IIv spacecraft. Results are presented using numerical integration of the force model and long-arc
satellite laser ranging (SLR) analysis. The integrated trajectory differs from a precise orbit calculated using a network
of global tracking stations by circa 2 m root mean square over a 160 000-km arc. The observed − computed residuals for the
400-day SLR arc are circa 28 mm.
Received: 23 December 1999 / Accepted: 28 August 2000 相似文献
13.
Three long series of tidal gravity observations, totalizing approximately 24 years and recorded with three superconducting
gravimeters, T004, T008, and T009, at stations Wuhan (China) and Kyoto (Japan), are studied. The tidal amplitude factors and
phase differences are determined precisely using Eterna and Nsv techniques. The precision of the main tidal amplitudes is
at the same level of 0.01 μGal. The atmospheric gravity signals are corrected using the coefficients determined with a regression
method between tidal gravity residual and station air pressure. The oceanic gravity signals are modeled based on five global
oceanic models. It is found that the oceanic models developed by the analysis of measurements from Topex/Poseidon altimeters
have the best fit to the superconducting gravimeter measurements, since the observed residuals and the discrepancies between
the amplitude factors and the theoretical tidal models are reduced more significantly. The long-period gravity variations
are dominated by the non-linear drift phenomena of the instruments, and the short-term variations in gravity are due to the
background noise at the stations.
Received: 20 January 2000 / Accepted: 15 September 2000 相似文献
14.
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
15.
As shown in previous work, dynamical effects of a realistic model of a heterogeneous, compressible, stably stratified liquid
core may be obtained by means of a simple analysis of the generalized two-dimensional Laplace tidal equation which describes
tidal flows of an incompressible and non-gravitating fluid in a thin spherical layer with mobile boundaries. The solution
was presented in the form of expansions in powers of a small parameter κ being the ratio of nutational motion frequency in
space to the frequency of the Earth's diurnal rotation. Whereas in an earlier paper only first-order terms were taken into
account, our present approach includes not only main second-order terms in the spherical harmonic expansions of the solutions,
but also the terms of higher orders. These effects are calculated numerically for realistic models of the Earth's outer liquid
core, solid inner core and anelastic mantle (PREM model). All tables are found in electronic version at http://www.tu-darmstadt.de/fb/vw/ipg/Welcome2.html
Received: 12 June 1997 / Accepted: 11 December 1997 相似文献
16.
Geographic boundary analysis is a relatively new approach unfamiliar to many spatial analysts. It is best viewed as a technique
for defining objects – geographic boundaries – on spatial fields, and for evaluating the statistical significance of characteristics
of those boundary objects. This is accomplished using null spatial models representative of the spatial processes expected
in the absence of boundary-generating phenomena. Close ties to the object-field dialectic eminently suit boundary analysis
to GIS data. The majority of existing spatial methods are field-based in that they describe, estimate, or predict how attributes
(variables defining the field) vary through geographic space. Such methods are appropriate for field representations but not
object representations. As the object-field paradigm gains currency in geographic information science, appropriate techniques
for the statistical analysis of objects are required. The methods reviewed in this paper are a promising foundation. Geographic
boundary analysis is clearly a valuable addition to the spatial statistical toolbox.? This paper presents the philosophy of,
and motivations for geographic boundary analysis. It defines commonly used statistics for quantifying boundaries and their
characteristics, as well as simulation procedures for evaluating their significance. We review applications of these techniques,
with the objective of making this promising approach accessible to the GIS-spatial analysis community. We also describe the
implementation of these methods within geographic boundary analysis software: GEM.
Received: 22 March 1999 / Accepted: 7 September 1999 相似文献
17.
We present an empirical model for periodic variations of diurnal and sub-diurnal Earth rotation parameters (ERPs) that was
derived based on the transformation of normal equation (NEQ) systems of Very Long Baseline Interferometry (VLBI) observing
sessions. NEQ systems that contain highly resolved polar motion and UT1-TAI with a temporal resolution of 15 min were generated
and then transformed to the coefficients of the tidal ERP model to be solved for. To investigate the quality of this model,
comparisons with empirical models from the Global Positioning System (GPS), another VLBI model and the model adopted by the
conventions of the International Earth Rotation and Reference Systems Service (IERS) were performed. The absolute coefficients
of these models agree almost completely within 7.5 μ as in polar motion and 0.5 μ s in UT1-TAI. Several bigger differences exist, which are discussed in this paper. To be able to compare the model estimates
with results of the continuous VLBI campaigns, where signals with periods of 8 and 6 h were detected, terms in the ter- and
quarter-diurnal band were included in the tidal ERP model. Unfortunately, almost no common features with the results of continuous
VLBI campaigns or ERP predictions in these tidal bands can be seen. 相似文献
18.
Vertical velocities of 30 European permanent Global Positioning System (GPS) stations at or close to tide gauge sites are estimated from more than 3 years of continuous observations. The results of two different solution strategies are presented and compared. The first approach accumulates the daily free network normal equations, the second introduces all sets of daily ellipsoidal height estimates and their covariance matrix into a subsequent common least squares adjustment. In both solutions, mean station heights at a reference epoch, linear vertical velocities, height discontinuities and short period height offsets are estimated. The second approach solves in addition for periodic annual signals and for site-specific pressure loading coefficients. The vertical velocities range from +8 mm/year in the center of the Fennoscandian uplift area to –4 mm/year at a few subsiding locations. Apart from these extrema, most of the sites experience only very small vertical motions. The standard deviations from the second approach providing more realistic error estimates are well below 0.15 mm/year. Some specific data problems are discussed. 相似文献
19.
Existing position information in a network can be integrated with the densification solution in two ways: One way is to obtain
a solution of the densification network followed by a merger of this and all other solutions or vice versa. Alternatively,
the existing solutions (not used as weighted constraints) can be taken to be pseudo-observations in a simultaneous adjustment
with the “new” observations. In both cases, all existing solutions must first be transformed to the coordinate system of the
densified network and be statistically compatible with it. Simultaneous densification and integration is discussed through
mathematical adjustment models in which the geometrical strength of networks is underscored. The rationale behind densifying
and integrating networks either in two different steps or simultaneously is analyzed. It is concluded that the simultaneous
approach should be avoided unless the various solutions turn out to be statistically compatible. 相似文献
20.
Autoregressive and moving average models for temporally dynamic networks treat time as a series of discrete steps which assumes even intervals between data measurements and can introduce bias if this assumption is not met. Using real and simulated data from the London Underground network, this paper illustrates the use of continuous time multilevel models to capture temporal trajectories of edge properties without the need for simultaneous measurements, along with two methods for producing interpretable summaries of model results. These including extracting ‘features’ of temporal patterns (e.g. maxima, time of maxima) which have utility in understanding the network properties of each connection and summarising whole-network properties as a continuous function of time which allows estimation of network properties at any time without temporal aggregation of non-simultaneous measurements. Results for temporal pattern features in the response variable were captured with reasonable accuracy. Variation in the temporal pattern features for the exposure variable was underestimated by the models. The models showed some lack of precision. Both model summaries provided clear ‘real-world’ interpretations and could be applied to data from a range of spatio-temporal network structures (e.g. rivers, social networks). These models should be tested more extensively in a range of scenarios, with potential improvements such as random effects in the exposure variable dimension. 相似文献
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