共查询到20条相似文献,搜索用时 33 毫秒
1.
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: |
2.
Phase center modeling for LEO GPS receiver antennas and its impact on precise orbit determination 总被引:12,自引:5,他引:7
Adrian Jäggi R. Dach O. Montenbruck U. Hugentobler H. Bock G. Beutler 《Journal of Geodesy》2009,83(12):1145-1162
Most satellites in a low-Earth orbit (LEO) with demanding requirements on precise orbit determination (POD) are equipped with
on-board receivers to collect the observations from Global Navigation Satellite systems (GNSS), such as the Global Positioning
System (GPS). Limiting factors for LEO POD are nowadays mainly encountered with the modeling of the carrier phase observations,
where a precise knowledge of the phase center location of the GNSS antennas is a prerequisite for high-precision orbit analyses.
Since 5 November 2006 (GPS week 1400), absolute instead of relative values for the phase center location of GNSS receiver
and transmitter antennas are adopted in the processing standards of the International GNSS Service (IGS). The absolute phase
center modeling is based on robot calibrations for a number of terrestrial receiver antennas, whereas compatible antenna models
were subsequently derived for the remaining terrestrial receiver antennas by conversion (from relative corrections), and for
the GNSS transmitter antennas by estimation. However, consistent receiver antenna models for space missions such as GRACE
and TerraSAR-X, which are equipped with non-geodetic receiver antennas, are only available since a short time from robot calibrations.
We use GPS data of the aforementioned LEOs of the year 2007 together with the absolute antenna modeling to assess the presently
achieved accuracy from state-of-the-art reduced-dynamic LEO POD strategies for absolute and relative navigation. Near-field
multipath and cross-talk with active GPS occultation antennas turn out to be important and significant sources for systematic
carrier phase measurement errors that are encountered in the actual spacecraft environments. We assess different methodologies
for the in-flight determination of empirical phase pattern corrections for LEO receiver antennas and discuss their impact
on POD. By means of independent K-band measurements, we show that zero-difference GRACE orbits can be significantly improved
from about 10 to 6 mm K-band standard deviation when taking empirical phase corrections into account, and assess the impact
of the corrections on precise baseline estimates and further applications such as gravity field recovery from kinematic LEO
positions. 相似文献
3.
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 |
4.
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: |
5.
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: |
6.
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 |
7.
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: |
8.
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: |
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.
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: |
11.
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: |
12.
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: |
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.
Engineering projects that require deformation monitoring frequently utilize geodetic sensors to measure displacements of target
points located in the deformation zone. In situations where control stations and targets are separated by a kilometer or more,
GPS can offer higher precision position updates at more frequent intervals than can normally be achieved using total station
technology. For large-scale deformation projects requiring the highest precision, it is therefore advisable to use a combination
of the two sensors. In response to the need for high precision, continuous GPS position updates in harsh deformation monitoring
environments, a software has been developed that employs triple-differenced carrier-phase measurements in a delayed-state
Kalman filter. Two data sets were analyzed to test the capabilities of the software. In the first test, a GPS antenna was
displaced using a translation stage to mimic slow deformation. In the second test, data collected at a large open pit mine
were processed. It was shown that the delayed-state Kalman filter developed could detect millimeter-level displacements of
a GPS antenna. The actual precision attained depends upon the amount of process noise infused at each epoch to accommodate
the antenna displacements. Higher process noise values result in quicker detection times, but at the same time increase the
noise in the solutions. A slow, 25 mm displacement was detected within 30 min of the full displacement with sigma values in
E, N and U of ±10 mm or better. The same displacement could also be detected in less than 5 h with sigma values in E, N and U of ±5 mm or better. The software works best for detecting long period deformations (e.g., 20 mm per day or less) for which
sigma values of 1–2 mm are attained in all three solution components. It was also shown that the triple-differenced carrier-phase
observation can be used to significantly reduce the effects of residual tropospheric delay that would normally plague double-differenced
observations in harsh GPS environments.
相似文献
Don KimEmail: |
15.
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: |
16.
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: |
17.
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: |
18.
Tzu-Pang Tseng Kefei Zhang Cheinway Hwang Urs Hugentobler Chuan-Sheng Wang Suelynn Choy Yi-Shan Li 《GPS Solutions》2014,18(2):219-230
We provide suggestions for the approved COSMIC-2 satellite mission regarding the field of view (FOV) and the clock stability of its future GNSS receiver based on numerical analyses using COSMIC GPS data. While the GRACE GPS receiver is mounted on the zenith direction, the precise orbit determination (POD) antennas of COSMIC are not. The COSMIC antenna design results in a narrow FOV and a reduction in the number of GPS observations. To strengthen the GPS geometry, GPS data from two POD antennas of COSMIC are used to estimate its orbits. The phase residuals of COSMIC are at the centimeter level, compared to the millimeter level of GRACE. The receiver clock corrections of COSMIC and GRACE are at the microsecond and nanosecond levels, respectively. The clock spectra of COSMIC at the frequencies of 0–0.005 Hz contain significant powers, indicating potential systematic errors in its clock corrections. The clock stability, expressed by the Allan deviation, of COSMIC ranges from 10?9 to 10?11 over 1 to 104 s, compared to 10?12 to 10?14 for GRACE. Compared to USO-based clock of GRACE, the clock of COSMIC is degraded in its stability and is linked to the reduction of GPS data quality. Lessons for improvement of COSMIC-2 over COSMIC in FOV and receiver clock stability are given. 相似文献
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.
Network-based geometry-free three carrier ambiguity resolution and phase bias calibration 总被引:5,自引:2,他引:3
Continuously operating reference stations (CORS) are increasingly used to deliver real-time and near-real-time precise positioning
services on a regional basis. A CORS network-based data processing system uses either or both of the two types of measurements:
(1) ambiguity-resolved double-differenced (DD) phase measurements, and (2) phase bias calibrated zero-differenced (ZD) phase
measurements. This paper describes generalized, network-based geometry-free models for three carrier ambiguity resolution
(TCAR) and phase bias estimation with DD and ZD code and phase measurements. First, the geometry-free TCAR models are constructed
with two Extra-Widelane (EWL)/Widelane (WL) virtual observables to allow for rapid ambiguity resolution (AR) for DD phase
measurements without distance constraints. With an ambiguity-resolved WL phase measurement and the ionospheric estimate derived
from the two EWL observables, an additional geometry-free equation is formed for the third virtual observable linearly independent
of the previous two. AR with the third geometry-free model requires a longer period of observations for averaging than the
first two, but is also distance-independent. A more general formulation of the geometry-free model for a baseline or network
is also introduced, where all the DD ambiguities can be more rigorously resolved using the LAMBDA method. Second, the geometry-free
models for calibration of three carrier phase biases of ZD phase measurements are similarly defined for selected virtual observables.
A network adjustment procedure is then used to improve the ZD phase biases with known DD integer constraints. Numerical results
from experiments with 24-h dual-frequency GPS data from three US CORS stations baseline lengths of 21, 56 and 74 km confirm
the theoretical predictions concerning AR reliability of the network-based geometry-free algorithms.
相似文献
Chris RizosEmail: |