共查询到20条相似文献,搜索用时 531 毫秒
1.
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: |
2.
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: |
3.
In this article, an algorithm for clock offset estimation of the GPS satellites is presented. The algorithm is based on a
Kalman-filter and processes undifferenced code and carrier-phase measurements of a global tracking network. The clock offset
and drift of the satellite clocks are estimated along with tracking station clock offsets, tropospheric zenith path delay
and carrier-phase ambiguities. The article provides a brief overview of already existing near-real-time and real-time clock
products. The filter algorithm and data processing scheme is presented. Finally, the accuracy of the orbit and clock product
is assessed with a precise orbit determination of the MetOp satellite and compared to results gained with other real-time
products.
相似文献
André HauschildEmail: |
4.
This study adopts the Chiu-fen-erh-shan landslide as a case study for incorporating comprehensive accelerograph and global
positioning system (GPS) data to determine the best-fit acceleration data for analyzing a rock avalanche. Previous investigations
indicate that the distance from an accelerograph to a landslide site is crucial to determining the best-fit acceleration data
to use in conducting a seismic analysis. Unfortunately, the Chiu-fen-erh-shan landslide and its nearest accelerograph station
are located in different geological zones. Thus, GPS data were compared to the displacements derived from the accelerograms
of nearby monitoring stations to help select the best accelerograph data. This emphasizes that a high density distribution
of accelerographs and GPS installations are essential to acquire the best data for the seismic analysis, especially in complex
geological zones. After applying the best-fit accelerogram to Newmark’s sliding model and an empirical displacement attenuation
formula to back-calculate the shear strength parameters of the sliding surface, a cohesion of 0 kPa and friction angle of
the sliding surface of 24.8° were found for this landslide.
相似文献
Jian-Hong WuEmail: Email: |
5.
The accuracy of standalone GPS positioning improved significantly when Selective Availability was turned off in May 2000. With the availability of various public GPS related products including precise satellite orbits and clocks, and ionosphere maps, a single-frequency standalone user can experience even a further improvement of the position accuracy. Next, using carrier phase measurements becomes crucial to smoothen the pseudorange noise. In this contribution, the most critical sources of error in single-frequency standalone positioning will be reviewed and different approaches to mitigate the errors will be considered. An optimal filter (using also carrier phase measurements) will be deployed. The final approach will then be evaluated in a decently long static test with receivers located in different regions of the world. Kinematic experiments have also been performed in various scenarios including a highly dynamic flight trial. The accuracy, in general, can be confirmed at 0.5 m horizontal and 1 m vertical, with static tests. Ultimate results demonstrate an accuracy close to 2 dm (95%) for the horizontal position components and 5 dm (95%) for the vertical in the flight experiment.
相似文献
Anh Quan LeEmail: |
6.
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: |
7.
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: |
8.
Computer algebra solution of the GPS N-points problem 总被引:1,自引:0,他引:1
A computer algebra solution is applied here to develop and evaluate algorithms for solving the basic GPS navigation problem: finding a point position using four or more pseudoranges at one
epoch (the GPS N-points problem). Using Mathematica 5.2 software, the GPS N-points problem is solved numerically, symbolically, semi-symbolically, and with Gauss–Jacobi, on a work station. For the case of N > 4, two minimization approaches based on residuals and distance norms are evaluated for the direct numerical solution and their computational duration is compared. For N = 4, it is demonstrated that the symbolic computation is twice as fast as the iterative direct numerical method. For N = 6, the direct numerical solution is twice as fast as the semi-symbolic, with the residual minimization requiring less computation
time compared to the minimization of the distance norm. Gauss–Jacobi requires eight times more computation time than the direct
numerical solution. It does, however, have the advantage of diagnosing poor satellite geometry and outliers. Besides offering
a complete evaluation of these algorithms, we have developed Mathematica 5.2 code (a notebook file) for these algorithms (i.e., Sturmfel’s resultant, Dixon’s resultants, Groebner basis, reduced
Groebner basis and Gauss–Jacobi). These are accessible to any geodesist, geophysicist, or geoinformation scientist via the
GPS Toolbox () website or the Wolfram Information Center ().
相似文献
Erik W. GrafarendEmail: |
9.
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: |
10.
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: |
11.
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: |
12.
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: |
13.
Small-scale irregularities in the background electron density of the ionosphere can cause rapid fluctuations in the amplitude
and phase of radio signals passing through it. These rapid fluctuations are known as scintillation and can cause a Global
Positioning System (GPS) receiver to lose lock on a signal. This could compromise the integrity of a safety of life system
based on GPS, operating in auroral regions. In this paper, the relationship between the loss of lock on GPS signals and ionospheric
scintillation in auroral regions is explored. The period from 8 to 14 November 2004 is selected for this study, as it includes
both geomagnetically quiet and disturbed conditions. Phase and amplitude scintillation are measured by GPS receivers located
at three sites in Northern Scandinavia, and correlated with losses of signal lock in receivers at varying distances from the
scintillation receivers. Local multi-path effects are screened out by rejection of low-elevation data from the analysis. The
results indicate that losses of lock are more closely related to rapid fluctuations in the phase rather than the amplitude
of the received signal. This supports the idea, suggested by Humphreys et al. (2005) (performance of GPS carrier tracking loops during ionospheric scintillations. Proceedings Internationsl Ionospheric Effects
Symposium 3–5 May 2005), that a wide loop bandwidth may be preferred for receivers operating at auroral latitudes. Evidence from the Imaging Riometer
for Ionospheric Studies (IRIS) appears to suggest that, for this particular storm, precipitation of particles in the D/E regions
may be the mechanism that drives the rapid phase fluctuations in the signal.
相似文献
Robert W. MeggsEmail: |
14.
A data archive of GPS navigation messages 总被引:2,自引:1,他引:1
Since 18 June 2007 navigation data messages transmitted by the GPS constellation are recorded by five receivers within GeoForschungsZentrum’s
global groundstation network. We describe the recording, processing, validation, analysis and archiving of the navigation
data. During the 197 days between 18 June 2007 and 31 December 2007 a total of 125,723,666 subframes were collected. By taking
into consideration that the same data set frequently is observed by two or more receivers concurrently, 65,153,955 unique
subframes could be extracted from the observations. With an estimated 88,099,200 subframes transmitted by the constellation
during this time period a data yield of about 74% was achieved. Simulation studies suggest that with two additional GPS receivers,
which are scheduled for addition to the network in 2008, about 95% of the transmitted subframes will be retrieved. The message
data archive is open to the scientific community for non-commercial purposes and may be accessed through GFZ’s Information
System and Data Center ().
相似文献
G. BeyerleEmail: |
15.
Ionospheric climatology derived from gps occultation observations made by the ionospheric occultation experiment 总被引:1,自引:1,他引:0
Paul Straus 《GPS Solutions》2005,9(2):164-173
The ionospheric occultation experiment (IOX) is a GPS occultation sensor with an ionospheric mission focus. IOX measurements of GPS L1 and L2 carrier phase during Earth limb views of setting GPS satellites are used together with the Abel transform to determine vertical profiles of electron density from which F-region peak parameters are determined. Data from a four and a half month period beginning in November 2001 are statistically binned and compared with a climatological model. To account for potential errors in interpretation that could arise from violation of the Abel transform assertion of spherical symmetry, the data are compared to both the climatology and to statistics of simulated ionospheric inversions using the climatological model. General characteristics of the climatology are reproduced by the occultation data. However, several significant discrepancies between the model and the data are observed during this near-solar maximum time period. In particular, average mid-latitude daytime densities are shown to be higher than the climatological prediction and the height of F2 layer in the post-sunset equatorial region is underestimated by up to 150 km.
相似文献
Paul StrausEmail: Phone: +1-310-3365328Fax: +1-310-3361636 |
16.
Although not considered for the first generation of European Galileo satellites, the use of C-Band frequencies for navigation purposes may be taken into account for a future generation of Galileo. For this reason, a frequency band of 20 MHz bandwidth (5,010–5,030 MHz) has been allocated in the course of the World Radio Communications Conference 2000 held in Istanbul, Turkey. The use of C-Band navigation signals offers both advantages and drawbacks. One example is the ionospheric path delay which is inversely proportional to the (squared) carrier frequency and is therefore significantly smaller at C-Band. On the other hand, the use of C-Band frequencies results in increased attenuation effects such as free space loss or rainfall attenuation. It is therefore necessary to provide a detailed analysis of the effects of C-Band frequencies on the navigation process. In order to assess the feasibility of using C-Band frequencies, various aspects of signal propagation and satellite signal tracking at C-Band are examined in the context of this article. In particular, aspects like free space loss, atmospheric effects, foliage attenuation, code and carrier tracking performance, code noise, phase noise and multipath are discussed with respect to their performance at C-Band. In order to allow comparison with the current GPS system, the performance at C-Band is compared to the L-Band performance under similar or identical conditions. The results of this analysis will finally be discussed with respect to their impact on satellite payload and receiver design.
相似文献
Markus IrsiglerEmail: Phone: +49-89-60043552Fax: +49-89-60043019 |
17.
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: |
18.
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 |
19.
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: |
20.
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: |