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1.
The EUREF permanent network (EPN) is a network of continuously operating global navigation satellite system (GNSS) stations, primarily installed for reference frame maintenance. In order to ensure the long term reliability of the EPN products, a thorough station performance monitoring has been initiated and carried out in addition to the routine GNSS data management, processing and analysis. This paper addresses the main factors influencing the quality of the coordinate time series in a permanent GNSS network. Relevant examples, based on the EPN experience are given, the analysis strategy is introduced, the estimated coordinate offsets are published and the importance of this analysis for site velocity estimation is demonstrated. The results are derived from the analysis of the EPN weekly combined solutions covering the period from 1996 to 2003. Our target is the identification, interpretation and elimination of offsets and outliers present in the EPN coordinate time series in order to estimate reliable coordinates and velocities and consequently maintain a high quality kinematic reference network.
相似文献
A. KenyeresEmail: Fax: +36-1-27374982 |
2.
Alan T. Murray Timothy C. Matisziw Tony H. Grubesic 《Journal of Geographical Systems》2007,9(2):103-117
Effective management of critical network infrastructure requires the assessment of potential interdiction scenarios. Optimization
approaches have been essential for identifying and evaluating such scenarios in networked systems. Although a primary function
of any network is the distribution of flow between origins and destinations, the complexity and difficulty of mathematically
abstracting interdiction impacts on connectivity or flow has been a challenge for researchers. This paper presents an optimization
approach for identifying interdiction bounds with respect to connectivity and/or flow associated with a system of origins
and destinations. Application results for telecommunications flow are presented, illustrating the capabilities of this approach.
相似文献
Alan T. Murray (Corresponding author)Email: |
Timothy C. MatisziwEmail: |
Tony H. GrubesicEmail: |
3.
Troposphere zenith path delays derived from the Global Data Assimilation System (GDAS) numerical weather model (NWM) are compared
with those of the International GNSS Service (IGS) solutions over a 1.5-year period at 18 globally distributed IGS stations.
Meteorological parameters can be interpolated from the NWM model at any location and at any time after December 2004. The
meteorological parameters extracted from the NWM model agree with in situ direct measurements at some IGS stations within
1 mbar for pressure, 3° for temperature and 13% for relative humidity. The hydrostatic and wet components of the zenith path
delay (ZPD) are computed using the meteorological parameters extracted from the NWM model. The total ZPDs derived from the
GDAS NWM agree with the IGS ZPD solutions at 3.0 cm RMS level with biases of up to 4.5 cm, which can be attributed to the
wet ZPDs estimates from the NWM model, considering the less accurate interpolated relative humidity parameter. Based on this
study, it is suggested that the availability and the precision of the GDAS NWM ZPD should be sufficient for nearly all GPS
navigation solutions.
相似文献
Constantin-Octavian AndreiEmail: |
4.
The ecological fallacy (EF) is a common problem regional scientists have to deal with when using aggregated data in their analyses. Although there is a wide number of studies considering different aspects of this problem, little attention has been paid to the potential negative effects of the EF in a time series context. Using Spanish regional unemployment data, this paper shows that EF effects are not only observed at the cross-section level, but also in a time series framework. The empirical evidence obtained shows that analytical regional configurations are the least susceptible to time effects relative to both normative and random regional configurations, while normative configurations are an improvement over random ones.
相似文献
Raúl RamosEmail: |
5.
Lambert Wanninger 《GPS Solutions》2009,13(2):133-139
Antenna changes at GNSS reference stations frequently produce discontinuities in the coordinate time series. These apparent
position shifts are mainly caused by changes of carrier-phase multipath effects and different errors in the antenna phase
center corrections. A monitoring method was developed and successfully tested, which requires additional GNSS observations
from a local, temporary reference station. Changes of carrier-phase measurement errors due to the antenna change are determined
and stored in L1 and L2 phase maps. These phase maps provide corrections to be applied either to the observation data obtained
before the antenna change or to the observation data obtained after the antenna change. The observation corrections are able
to remove coordinate discontinuities independent of the selected coordinate estimation algorithm.
相似文献
Lambert WanningerEmail: |
6.
Since the assumption of all stations tracking the same satellites with identical weights was previously employed by Shen and
Xu (GPS Solut 12:99–108, 2008) to derive the simplified GNSS single- and double-differenced equivalent equations, this supplementary paper expands these
simplified equations in the case of each station tracking different satellites with elevation-dependent weights. Numerical
experiments are performed to demonstrate the computational efficiency of the simplified equivalent algorithm relative to the
traditional method in various scenarios of multi-baseline solutions with tracking different satellites. The fast computational
speed of the simplified equivalent algorithm will potentially benefit the local, regional and even global GNSS multi-baseline
solutions as well as the combined GNSS application.
相似文献
Guochang XuEmail: |
7.
A constrained LAMBDA method for GPS attitude determination 总被引:4,自引:0,他引:4
An improved method to obtain fixed integer ambiguity in GPS attitude determination is presented. Known conditions are utilized
as constraints to acquire attitude information when the float solution and its variance–covariance matrix are not accurate
enough. The searching ellipsoidal region is first expanded to compensate for errors caused by the inaccurate float solution.
Then the constraints are used to shrink the region to a proper size, which maintains the true integer ambiguity. Experimental
results demonstrate that this scheme gives a fast search time and a higher success rate in determining the fixed integer ambiguity
than the unconstrained method. The accuracy of attitude angles is also improved.
相似文献
Bo WangEmail: |
8.
Reliability analysis is inseparably connected with the formulation of failure scenarios, and common test statistics are based on specific assumptions. This is easily overlooked when processing observation differences. Poor failure identification performance and misleading pre-analysis results, mainly meaningless minimum detectable biases and external reliability measures, are the consequence. A reasonable failure scenario for use with differenced GNSS observations is formulated which takes into account that individual outliers in the original data affect more than one processed observation. The proper test statistics and reliability indicators are given for use with correlated observations and both batch processing and Kalman filtering. It is also shown that standardized residuals and redundancy numbers fail completely when used with double differenced observations.
相似文献
Andreas WieserEmail: Phone: +43-316-8736323Fax: +43-316-8736820 |
9.
Total electron content processing from GPS observations to facilitate ionospheric modeling 总被引:2,自引:1,他引:1
With the increasing global distribution of high rate dual-frequency global positioning system (GPS) receivers, the production
of a real-time atmospheric constituent definition, total electron content (TEC), has become a beneficial contributor to the
modeling applications used in the assessment of GPS position accuracy and the composition of the ionosphere, plasmasphere,
and troposphere. Historically, TEC measurements have been obtained through post processing techniques to produce the quality
of data necessary for modeling applications with rigorous error estimate requirements. These procedures necessitated the collection
of large volumes of data to address the various abnormalities in the computation of TEC associated with the use of greater
data quality controls and source selection while real-time modeling environments must rely on autonomous controls and filtration
techniques to prevent the production of erroneous model results. In this paper we present methods for processing TEC in real
time, which utilize several procedures including the application of an ionospheric model to automatically perform quality
control on the TEC output and the computational techniques used to address receiver multipath, faulty receiver observations,
cycle-slips, segmented processing, and receiver calibrations. The resulting TEC measurements are provided with rigorous error
estimates validated using the vertical TEC from the Jason satellite mission.
相似文献
Nelson A. BonitoEmail: |
10.
High-frequency multipath would be problematic for studies at seismic or antenna dynamical frequencies as one could mistakenly
interpret them as signals. A simple procedure to identify high-frequency multipath from global positioning system (GPS) time
series records is presented. For this purpose, data from four GPS base stations are analyzed using spectral analyses techniques.
Additional data, such as TEQC report files of L1 pseudorange multipath, are also used to analyze the high-frequency multipath
and confirmation of the high-frequency multipath inferred from the phase records. Results show that this simple procedure
is effective in identification of high-frequency multipath. The inferred information can aid interpretation of multipath at
the GPS site, and is important for a number of reasons. For example, the information can be used to study GPS site selections
and/or installations.
相似文献
Clement OgajaEmail: |
11.
Incorporating spatial variation in housing attribute prices: a comparison of geographically weighted regression and the spatial expansion method 总被引:10,自引:3,他引:7
Christopher Bitter Gordon F. Mulligan Sandy Dall’erba 《Journal of Geographical Systems》2007,9(1):7-27
Hedonic house price models typically impose a constant price structure on housing characteristics throughout an entire market
area. However, there is increasing evidence that the marginal prices of many important attributes vary over space, especially
within large markets. In this paper, we compare two approaches to examine spatial heterogeneity in housing attribute prices
within the Tucson, Arizona housing market: the spatial expansion method and geographically weighted regression (GWR). Our
results provide strong evidence that the marginal price of key housing characteristics varies over space. GWR outperforms
the spatial expansion method in terms of explanatory power and predictive accuracy.
相似文献
Christopher BitterEmail: |
12.
Separate space- or time-lags have been considered regularly in data analyses; as space–time models are more recently being
studied extensively in data analytic fashion, joint estimation of both lags has to be considered explicitly. This paper addresses
this issue, taking into special consideration parametric parsimony together with specification richness; use of the bivariate
Poisson frequency distribution is advocated and applied to an empirical case. The relation of this approach to random effects
specifications is investigated. Data for Belgian regional products constitute the empirical case study.
相似文献
Daniel A. GriffithEmail: |
13.
Digital mobile mapping, the method that integrates digital imaging with direct geo-referencing, has developed rapidly over
the past 15 years. The Kalman filter (KF) is considered an optimal estimation tool for real-time INS/GPS integrated kinematic
positioning and orientation determination. However, the accuracy requirements of general mobile mapping applications cannot
be easily achieved even when using the KF scheme. Therefore, this study proposes an intelligent scheme combining ANN and RTS
backward smoother to overcome the limitations of KF and to enhance the overall accuracy of attitude determination for tactical
grade and MEMS INS/GPS integrated systems.
相似文献
Yun-Wen Huang (Corresponding author)Email: |
14.
Identifying barriers of species and characterize their effects on spatial distribution provide essential information to research
in landscape genetics. We propose a weighted difference barrier (WDB) method as an alternative to maximum difference barriers
(MDB), and to initiate and integrate more spatial modeling and methods into the problem solving process. Overall, WDB provides
quick and straightforward improvements to the drawbacks of MDB. WDB integrates more sample location relationships into the
barrier construction and reveals potential barriers that would otherwise go undetected. WDB incorporates both within group
and between group genetic information, and delineates the barriers as a more complex pattern.
相似文献
John RadkeEmail: |
15.
Fast direct GPS P-Code acquisition 总被引:5,自引:0,他引:5
GPS P-Code has a higher chipping rate, better accuracy, and anti-jamming property than C/A code. Traditionally, GPS P-Code acquisition depends on handover from C/A code. This potentially needs long acquisition time. Moreover, when C/A code is not available, it is no longer possible to acquire GPS P-Code through handover from C/A code. The purpose of this paper is to describe a new overlap average method to facilitate hardware design of fast direct P-Code acquisition. It allows the rapid code phase search to acquire GPS P-Code signals, and also decreases the hardware resource requirement. The small size FFT in the proposed methods is very promising for fast FPGA hardware system design using FFT cores. The simulation results and theoretical analysis are included demonstrating the overall performance of the proposed method.
相似文献
Jing PangEmail: Phone: +1-916-2784549Fax: +1-916-2787215 |
16.
Show me the code: spatial analysis and open source 总被引:3,自引:1,他引:2
Sergio J. Rey 《Journal of Geographical Systems》2009,11(2):191-207
This paper considers the intersection of academic spatial analysis with the open source revolution. Its basic premise is that
the potential for cross-fertilization between the two is rich, yet some misperceptions about these two communities pose challenges
to realizing these opportunities. The paper provides a primer on the open source movement for academicians with an eye towards
correcting these misperceptions. It identifies a number of ways in which increased adoption of open source practices in spatial
analysis can enhance the development of the next generation of tools and the wider practice of scientific research and education.
相似文献
Sergio J. ReyEmail: |
17.
Modeling spatial autocorrelation in spatial interaction data: empirical evidence from 2002 Germany journey-to-work flows 总被引:3,自引:3,他引:0
Daniel A. Griffith 《Journal of Geographical Systems》2009,11(2):117-140
Since before the inception of work by Okabe, the intermingling of spatial autocorrelation (i.e., local distance and configuration)
and distance decay (i.e., global distance) effects has been suspected in spatial interaction data. This convolution was first
treated conceptually because technology and methodology did not exist at the time to easily or fully address spatial autocorrelation
effects within spatial interaction model specifications. Today, however, sufficient computer power coupled with eigenfunction-based
spatial filtering offers a means for accommodating spatial autocorrelation effects within a spatial interaction model for
modest-sized problems. In keeping with Okabe’s more recent efforts to dissemination spatial analysis tools, this paper summarizes
how to implement the methodology utilized to analyze a particular empirical flows dataset.
相似文献
Daniel A. GriffithEmail: |
18.
In this paper a MATLAB toolbox for determining the attitude of a rigid platform by means of multiple non-dedicated antennas
using global positioning system is presented. The programs embedded in this toolbox cover the RINEX data analysis, single
point positioning, differential positioning, coordinate conversion, attitude determination, and other auxiliary functions.
After forming the baselines through double-differenced (carrier phase smoothed) code observables, the attitude parameters
are obtained by applying the direct attitude computation and the least squares attitude estimation. The theoretical background
is summarized, and some hints regarding the software implementation are given in the paper. Moreover, improvements yielding
an expanded functionality are proposed.
相似文献
Zhen DaiEmail: |
19.
Latent lifestyle preferences and household location decisions 总被引:3,自引:2,他引:1
Lifestyle, indicating preferences towards a particular way of living, is a key driver of the decision of where to live. We
employ latent class choice models to represent this behavior, where the latent classes are the lifestyles and the choice model
is the choice of residential location. Thus, we simultaneously estimate lifestyle groups and how lifestyle impacts location
decisions. Empirical results indicate three latent lifestyle segments: suburban dwellers, urban dwellers, and transit-riders.
The suggested lifestyle segments have intriguing policy implications. Lifecycle characteristics are used to predict lifestyle
preferences, although there remain significant aspects that cannot be explained by observable variables.
相似文献
Jieping LiEmail: |
20.
Ionospheric delay corrections for single-frequency GPS receivers over Europe using tomographic mapping 总被引:3,自引:2,他引:1
The majority of navigation satellites receivers operate on a single frequency and experience a positioning error due to the
ionospheric delay. This can be compensated for using a variety of approaches that are compared in this paper. The study focuses
on the last solar maximum. A 4D tomographic imaging technique is used to map the ionospheric electron density over the European
region during 2002 and 2003. The electron density maps are then used to calculate the excess propagation delay on the L1 frequency
experienced by GPS receivers at selected locations across Europe. The excess delay is applied to correct the pseudo-range
single frequency observations at each location and the improvements to the resulting positioning are calculated. The real-time
tomographic technique is shown to give navigation solutions that are better than empirical modelling methods and approach
the accuracy of the full dual-frequency solution. The improvements in positioning accuracy vary from day to day depending
on ionospheric conditions but can be up to 25 m during mid-day during these solar maximum conditions at European mid-latitudes.
相似文献
Damien J. AllainEmail: |