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1.
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: |
2.
Oliver Montenbruck Yago Andres Heike Bock Tom van Helleputte Jose van den Ijssel Marc Loiselet Christian Marquardt Pierluigi Silvestrin Pieter Visser Yoke Yoon 《GPS Solutions》2008,12(4):289-299
The global navigation satellite system receiver for atmospheric sounding (GRAS) on MetOp-A is the first European GPS receiver
providing dual-frequency navigation and occultation measurements from a spaceborne platform on a routine basis. The receiver
is based on ESA’s AGGA-2 correlator chip, which implements a high-quality tracking scheme for semi-codeless P(Y) code tracking
on the L1 and L2 frequency. Data collected with the zenith antenna on MetOp-A have been used to perform an in-flight characterization
of the GRAS instrument with focus on the tracking and navigation performance. Besides an assessment of the receiver noise
and systematic measurement errors, the study addresses the precise orbit determination accuracy achievable with the GRAS receiver.
A consistency on the 5 cm level is demonstrated for reduced dynamics orbit solutions computed independently by four different
agencies and software packages. With purely kinematic solutions, 10 cm accuracy is obtained. As a part of the analysis, an
empirical antenna offset correction and preliminary phase center correction map are derived, which notably reduce the carrier
phase residuals and improve the consistency of kinematic orbit determination results.
相似文献
Oliver MontenbruckEmail: |
3.
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: |
4.
In Global Navigation Satellite System (GNSS) positioning, the receiver measures the pseudorange with respect to each observable
navigation satellite and determines the position and clock bias. In addition to the GPS, several other navigation satellite
constellations including Glonass, Galileo and Compass can/will also be used to provide positioning, navigation, and timing
information. The paper is concerned with the solvability of the navigation problem when the receiver attempts to process measurements
from different constellations. As two different constellations may not be time-synchronized, the navigation problem involves
the determination of position of the receiver and clock bias with respect to each constellation. The paper describes an analytic
approach to account for the two-constellation navigation problem with three measurements from one constellation and two measurements
from another constellation. It is shown that the two-constellation GNSS navigation problem becomes the solving of a set of
two simultaneous quadratic equations or, equivalently, a quartic equation. Furthermore, the zero-crossover of the leading
coefficient and the sign of the discriminant of the quartic equation are shown to play a significant role in governing the
solvability, i.e., the existence and uniqueness of the navigation solutions.
相似文献
Jyh-Ching JuangEmail: |
5.
Oliver Montenbruck Miquel Garcia-Fernandez Yoke Yoon Steffen Schön Adrian Jäggi 《GPS Solutions》2009,13(1):23-34
Phase center variations of the receiver and transmitter antenna constitute a remaining uncertainty in the high precision orbit
determination (POD) of low Earth orbit (LEO) satellites using GPS measurements. Triggered by the adoption of absolute phase
patterns in the IGS processing standards, a calibration of the Sensor Systems S67-1575-14 antenna with GFZ choke ring has
been conducted that serves as POD antenna on various geodetic satellites such as CHAMP, GRACE and TerraSAR-X. Nominal phase
patterns have been obtained with a robotic measurement system in a field campaign and the results were used to assess the
impact of receiver antenna phase patterns on the achievable positioning accuracy. Along with this, phase center distortions
in the actual spacecraft environment were characterized based on POD carrier phase residuals for the GRACE and TerraSAR-X
missions. It is shown that the combined ground and in-flight calibration can improve the carrier phase modeling accuracy to
a level of 4 mm which is close to the pure receiver noise. A 3.5 cm (3D rms) consistency of kinematic and reduced dynamic
orbit determination solutions is achieved for TerraSAR-X, which presumably reflects the limitations of presently available
GPS ephemeris products. The reduced dynamic solutions themselves match the observations of high grade satellite laser ranging
stations to 1.5 cm but are potentially affected by cross-track biases at the cm-level. With respect to the GPS based relative
navigation of TerraSAR-X/TanDEM-X formation, the in-flight calibration of the antenna phase patterns is considered essential
for an accurate modeling of differential carrier phase measurements and a mm level baseline reconstruction.
相似文献
Oliver MontenbruckEmail: |
6.
The architecture of the ultra-tight GPS/INS/PL integration is the key to its successful performance; the main feature of this
architecture is the Doppler feedback to the GPS receiver tracking loops. This Doppler derived from INS, when integrated with
the carrier tracking loops, removes the Doppler due to vehicle dynamics from the GPS/PL signal thereby achieving a significant
reduction in the carrier tracking loop bandwidth. The bandwidth reduction provides several advantages such as: improvement
in anti-jamming performance, and increase in post correlated signal strength which in turn increases the dynamic range and
accuracy of measurements. Therefore, any degradation in the derived Doppler estimates will directly affect the tracking loop
bandwidth and hence its performance. The quadrature signals from the receiver correlator, I (in-phase) and Q (quadrature),
form the measurements, whereas the inertial sensor errors, position, velocity and attitude errors form the states of the complementary
Kalman filter. To specify a reliable measurement model of the filter for this type of integrated system, a good understanding
of GPS/PL signal characteristics is essential. It is shown in this paper that phase and frequency errors are the variables
that relate the measurements and the states in the Kalman filter. The main focus of this paper is to establish the fundamental
mathematical relationships that form the measurement model, and to show explicitly how the system error states are related
to the GPS/PL signals. The derived mathematical relationships encapsulated in a Kalman filter, are tested by simulation and
shown to be valid.
相似文献
Ravindra Babu (Corresponding author)Email: |
Jinling WangEmail: |
7.
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: |
8.
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: |
9.
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: |
10.
A sampling approach to estimate the log determinant used in spatial likelihood problems 总被引:2,自引:1,他引:1
Likelihood-based methods for modeling multivariate Gaussian spatial data have desirable statistical characteristics, but the
practicality of these methods for massive georeferenced data sets is often questioned. A sampling algorithm is proposed that
exploits a relationship involving log-pivots arising from matrix decompositions used to compute the log determinant term that
appears in the model likelihood. We demonstrate that the method can be used to successfully estimate log-determinants for
large numbers of observations. Specifically, we produce an log-determinant estimate for a 3,954,400 by 3,954,400 matrix in
less than two minutes on a desktop computer. The proposed method involves computations that are independent, making it amenable
to out-of-core computation as well as to coarse-grained parallel or distributed processing. The proposed technique yields
an estimated log-determinant and associated confidence interval.
相似文献
James P. LeSage (Corresponding author)Email: |
11.
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: |
12.
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: |
13.
Characterization of Compass M-1 signals 总被引:7,自引:4,他引:3
André Hauschild Oliver Montenbruck Jean-Marie Sleewaegen Lennard Huisman Peter J. G. Teunissen 《GPS Solutions》2012,16(1):117-126
An analysis of observations from China’s first medium earth orbit satellite Compass M-1 is presented, with main focus on the
first orbit and clock solution for this satellite. The orbit is computed from laser ranging measurements. Based on this orbit
solution, the apparent clock offset is estimated using measurements from two GNSS receivers, which allow Compass tracking.
The analysis of the clock solutions reveals unexpectedly high dynamics in the pseudorange and carrier-phase observations.
Furthermore, carrier-to-noise density ratio, pseudorange noise, and multipath are analyzed and compared to GPS and GIOVE.
The results of the clock analysis motivate further research on the signals of the geostationary satellites of the Compass
constellation. 相似文献
14.
M. E. O’Kelly 《Journal of Geographical Systems》2009,11(3):227-241
The minimax hub location problem sites a facility to minimize the maximum weighted interaction cost between pairs of fixed nodes. In this paper, distances are represented by a rectilinear norm and may be suited to factory layout or street
network problems. The problem is already well known (in 2-D) as the round trip location problem and is extended to 3-D in
this paper. One rationale for the solution method is based on an extension of the geometric arguments used to solve the minimax
single facility location problem. Suppose a budget is provided for interactions, and that each interaction must be accomplished
for no more than this cost. The algorithm uses a bi-section search for the feasible budget until it finds the expenditure
needed to provide for these flows. The extension in the present paper is that the nodes are permitted to be on different layers
(levels). This 3-D version of the problem appears to be a new variant of the hub model. The models and solution techniques
developed in the paper are illustrated using a small 55 node problem. Because of a relatively efficient implementation of
the bi-section search, the algorithm in 2-D and 3-D is also applied successfully to a 550 node problem.
相似文献
M. E. O’KellyEmail: |
15.
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: |
16.
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: |
17.
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: |
18.
Analysis of inversion errors of ionospheric radio occultation 总被引:3,自引:0,他引:3
The retrieved electron density profile of ionospheric radio occultation (RO) simulation data can be compared with the background
model value during the simulation and the inversion error can be obtained exactly. This paper studies the inversion error
of ionospheric RO through simulation. The sources of the inversion errors are analyzed. The impacts of measurement errors,
such as the errors in phase measurements and satellite orbits, are very small and can be neglected. The approximation of straight-line
propagation introduces errors at the height of the F1 layer under solar maximum condition. The spherical symmetry approximation
of the electron density distribution is found to be the main source of the inversion error. The statistical results reveal
some characteristics of the inversion errors. (1) The relative error increases with enhanced solar activity. (2) It is larger
in winter than in equinox season, and it is smallest in summer. (3) For all seasons, it is smaller at middle latitude than
at other latitudes. (4) For all seasons and geomagnetic latitudes, it is smaller at daytime than at other times. The NmF2
of the ROs from COSMIC are compared with the measurements of ionosondes, and the relative differences show the same dependencies
on season, geomagnetic latitude and local time, as the relative errors of the simulated ionospheric ROs.
相似文献
Xiaocheng WuEmail: |
19.
Pitch and roll attitude estimation of a small-scaled helicopter using single antenna GPS with gyroscopes 总被引:2,自引:2,他引:0
A method is presented for estimating the roll and pitch attitude of a small-scaled unmanned helicopter based on the velocity
measurements of the global positioning system (GPS). The small-scaled helicopter is a radio controlled (RC) model which is
readily available and affordable for academic laboratories as a research platform. Only one single antenna GPS receiver is
equipped on the RC helicopter to acquire the velocity measurements needed for the attitude estimation. The velocity information
is recorded by the onboard computer for post-processing. An attitude and heading reference system (AHRS) is used to provide
the reference attitudes. The required angular rates and heading for this study are also given by the gyroscopes and compass
of the AHRS for the sake of system’s simplification. The Kalman filter is applied to estimate the helicopter’s accelerations
by using the GPS velocity measurements. The estimated accelerations form the fundamental elements of synthesizing the pseudo-roll
and the pseudo-pitch. With some legitimate simplifications and assumptions, the relation between the helicopter’s attitudes
and the accelerations estimated from the GPS velocity measurements can be developed. Furthermore, to enhance the accuracy
of the pseudo-attitudes, the angular rates acquired from the gyroscopes are incorporated into the estimation algorithm of
pseudo-attitudes by using a complementary filter.
相似文献
Fei-Bin HsiaoEmail: |
20.
随着无人驾驶等高新技术的快速发展,实时精密单点定位在GNSS领域中受到越来越多的关注。研究实时卫星钟差的获取和实时定位精度具有较大的现实意义,本文为研究耦合BDS卫星轨道、钟差产品对定位精度的影响,采用不同精度的轨道产品实时获取卫星钟差。分析了卫星钟差误差与轨道误差之间的相关性及钟差对轨道误差的吸收能力,发现卫星钟差能够吸收95%以上的轨道径向误差和部分切线误差,在一定程度上弥补了轨道误差引起的定位误差。采用耦合的卫星轨道、钟差产品,单BDS系统定位精度可达到分米级的定位结果。 相似文献