共查询到20条相似文献，搜索用时 125 毫秒
1.
Hung Lee Jinling Wang Chris Rizos Dorota Grejner-Brzezinska Charles Toth 《GPS Solutions》2002,6(1-2):34-46
This paper discusses the introduction of pseudolites (ground-based GPS-like signal transmitters) into existing integrated
GPS/INS systems in order to provide higher availability, integrity, and accuracy in a local area. Even though integrated GPS/INS
systems can overcome inherent drawbacks of each component system (line-of-sight requirement for GPS, and INS errors that grow
with time), performance is nevertheless degraded under adverse operational circumstances. Some typical examples are when the
duration of satellite signal blockage exceeds an INS bridging level, resulting in large accumulated INS errors that cannot
be calibrated by GPS. Such a scenario, unfortunately, is a common occurrence for certain kinematic applications. To address
such shortcomings, both pseudolite/INS and GPS/pseudolite/INS integration schemes are proposed here. Typically, the former
is applicable for indoor positioning where the GPS signal is unavailable for use. The latter would be appropriate for system
augmentation when the number and geometry of visible satellites is not sufficient for accurate positioning or attitude determination.
In this paper, some technical issues concerned with implementing these two integration schemes are described, including the
measurement model, and the appropriate integration filter for INS error estimation and correction through GPS and pseudolite
(PL) carrier phase measurements. In addition, the results from the processing of simulated measurements, as well as field
experiments, are presented in order to characterize the system performance. As a result, it has been established that the
GPS/PL/INS and PL/INS integration schemes would make it possible to ensure centimeter-level positioning accuracy even if the
number of GPS signals is insufficient, or completely unavailable.
Electronic Publication 相似文献
2.
Single receiver phase ambiguity resolution with GPS data 总被引：26，自引：12，他引：14
Willy Bertiger Shailen D. Desai Bruce Haines Nate Harvey Angelyn W. Moore Susan Owen Jan P. Weiss 《Journal of Geodesy》2010,84(5):327-337
Global positioning system (GPS) data processing algorithms typically improve positioning solution accuracy by fixing double-differenced
phase bias ambiguities to integer values. These “double-difference ambiguity resolution” methods usually invoke linear combinations
of GPS carrier phase bias estimates from pairs of transmitters and pairs of receivers, and traditionally require simultaneous
measurements from at least two receivers. However, many GPS users point position a single local receiver, based on publicly
available solutions for GPS orbits and clocks. These users cannot form double differences. We present an ambiguity resolution
algorithm that improves solution accuracy for single receiver point-positioning users. The algorithm processes dual- frequency
GPS data from a single receiver together with wide-lane and phase bias estimates from the global network of GPS receivers
that were used to generate the orbit and clock solutions for the GPS satellites. We constrain (rather than fix) linear combinations
of local phase biases to improve compatibility with global phase bias estimates. For this precise point positioning, no other
receiver data are required. When tested, our algorithm significantly improved repeatability of daily estimates of ground receiver
positions, most notably in the east component by approximately 30% with respect to the nominal case wherein the carrier biases
are estimated as real values. In this “static” test for terrestrial receiver positions, we achieved daily repeatability of
1.9, 2.1 and 6.0 mm in the east, north and vertical (ENV) components, respectively. For kinematic solutions, ENV repeatability
is 7.7, 8.4, and 11.7 mm, respectively, representing improvements of 22, 8, and 14% with respect to the nominal. Results from
precise orbit determination of the twin GRACE satellites demonstrated that the inter-satellite baseline accuracy improved
by a factor of three, from 6 to 2 mm up to a long-term bias. Jason-2/Ocean Surface Topography Mission precise orbit determination
tests results implied radial orbit accuracy significantly below the 10 mm level. Stability of time transfer, in low-Earth
orbit, improved from 40 to 7 ps. We produced these results by applying this algorithm within the Jet Propulsion Laboratory’s
(JPL’s) GIPSY/OASIS software package and using JPL’s orbit and clock products for the GPS constellation. These products now
include a record of the wide-lane and phase bias estimates from the underlying global network of GPS stations. This implies
that all GIPSY–OASIS positioning users can now benefit from this capability to perform single-receiver ambiguity resolution. 相似文献
3.
4.
GNSS data management and processing with the GPSTk 总被引：2，自引：0，他引：2
Dagoberto Salazar Manuel Hernandez-Pajares Jose M. Juan Jaume Sanz 《GPS Solutions》2010,14(3):293-299
We organize complex problems in simple ways using a GNSS data management strategy based on “GNSS Data Structures” (GDS), coupled
with the open source “GPS Toolkit” (GPSTk) suite. The code resulting from using the GDS and their associated “processing paradigm”
is remarkably compact and easy to follow, yielding better code maintainability. Furthermore, the data abstraction allows flexible
handling of concepts beyond mere data encapsulation, including programmable general solvers. An existing GPSTk class can be
modified to achieve the goal. We briefly describe the “GDS paradigm” and show how the different GNSS data processing “objects”
may be combined in a flexible way to develop data processing strategies such as Precise Point Positioning (PPP) and network-based
PPP that computes satellite clock offsets on-the-fly. 相似文献
5.
The availability of GPS signals is a major concern for many existing and potential applications. Fortunately, with the development of Galileo by the European Commission (EC) and European Space Agency (ESA) and new funding for the restoration of the Russian GLONASS announced by the Russian Federation (Revnivykh et al., in European Navigation Conference 2005, Munich, Germany, July 19–22), the future for satellite-based positioning and navigation applications is extremely promising. With the complete cooperation from all these global navigation satellite systems (GNSS), greater levels of satellite visibility and therefore integrity can be expected. In this paper, a receiver autonomous integrity monitoring (RAIM) scheme along with reliability and separability measures are used to assess integrity performance levels of standalone GPS and integrated GPS/GLONASS, GPS/Galileo and GPS/GLONASS/Galileo systems where the clock offsets for each of the additional systems are estimated. It is shown, herein, that a minimum of three satellites must be visible in an additional system in order to provide a full integrity contribution when the system’s clock offset is to be estimated within the adjustment. A comparison of the integrity results obtained via system clock offsets estimated in the adjustment versus the case where the offsets are known and the measurements are corrected prior to the adjustment is also made for a high elevation mask scenario. Global simulation results for combined GPS/GLONASS/Galileo show that, theoretically, for the time of simulation and for any point on the globe, an outlier of 20 m can be detected with 80% probability at the 0.5% significance level and then separated from any other measurement with 90% probability. Corresponding values for the GPS only and combined GPS/GLONASS and GPS/Galileo systems, respectively, are approximately 435, 110 and 28 m, respectively, for the maximum MSBs and 312, 50 and 26 m, respectively, for the maximum MDBs. Temporal 24 h simulations for the GPS/GLONASS/Galileo scenario delivered agreeable results with the global snapshots for a 15° elevation mask. For the case where system clock offsets are estimated within the adjustment, it was shown that only the reliability measure was available for 100% of the time, with horizontal external reliability values of no more than about 12 m when a 30° masking angle was used. By assuming the clock offsets were determined and corrected for prior to the adjustment, the separability measure was markedly improved and was also available 100% of the time. 相似文献
6.
Michael E. Jackson Chuck Meertens Oivind Ruud Spencer Reeder Warren Gallaher Chris Rocken 《GPS Solutions》2002,5(4):10-19
The University NAVSTAR Consortium (UNAVCO) Boulder Facility is assessing Very Small Aperture Terminal (VSAT) technology for
near real-time transmission of GPS data from a remote receiver to a central processing facility. The study is motivated by
the need for a robust, cost-effective data communications solutions to transfer GPS data from remote sites where no other
communication alternatives exist. Future large-scale plate boundary deformation initiatives using spatially dense networks
of GPS will require receivers to be located where the science dictates, and not the power or communications infrastructure.
For other applications, such as determining rapid GPS orbits and time transfer, there is a push toward reducing the latency
in GPS data used to produce GPS data products and differential corrections (Talaya & Bosch, 1999; Jackson, Meertens, & Rocken,
2000; Muellerschoen, Bar-Sever, Bertiger, & Stowers, 2001), and to support upcoming Low Earth Orbiting (LEO) missions requiring
low latency, 1-s GPS data. In this paper we evaluate two Ku-band systems, the Nanometrics Libra VSAT and the StarBand 2-way
satellite Internet VSAT. The Nanometrics system test results show that continuous, 1-s GPS data can be streamed from multiple
remote stations within the VSAT footprint, quality checked, and delivered for processing with a <2.5-s latency (mean 1.2 s)
and a 99.8% reliability. Benefits of the Nanometrics system include global coverage, control of bandwidth allocation and data
hub, and the low power draw of the system. Negatives include the cost of hub and remote infrastructure and the need to negotiate
landing rights issues on a country-by-country basis. The UNAVCO Facility currently operates a Nanometrics hub and three remote
VSAT systems.
The StarBand system showed 98.9% reliability with a maximum latency of 10.2 s (mean latency 1.7 s) for 1-Hz GPS data and an
average uplink speed of 31.7 kbps. Benefits of the StarBand system include the cost and small profile of the remote antenna.
Negatives include coverage limited to coterminous United States and the high power draw of remote systems. ? 2002 Wiley Periodicals,
Inc. 相似文献
7.
Summary The signals transmitted by Block II satellites of the Global Positioning System (GPS) can be degraded to limit the highest accuracy of the system (10 m or better point positioning) to authorized users. This mode of degraded operation is called Selective Availability (S/A). S/A involves the degradation in the quality of broadcast orbits and satellite clock dithering. We monitored the dithered satellite oscillator and investigated the effect of this clock dithering on high accuracy relative positioning. The effect was studied over short 3-meter and zero-baselines with two GPS receivers. The equivalent S/A effects for baselines ranging from 0 to >10,000 km can be examined with short test baselines if the receiver clocks are deliberately mis-synchronized by a known and varying amount. Our results show that the maximum effect of satellite clock dithering on GPS double difference phase residuals grows as a function of the clock synchronization error according to: S/A
effect
=0.04 cm/msec, and it increases as a function of baseline length like: S/A
effect
=0.014 cm/100 km. These are equations for maximum observed values of post-fit residuals due to S/A. The effect on GPS baselines is likely to be smaller than the 0.14 mm for a baseline separation of 100 km. We therefore conclude, for our limited data set, and for the level of S/A during our tests, that S/A clock dithering has negligible effect on all terrestrial GPS baselines if double difference processing techniques are employed and if the GPS receivers remain synchronized to better than 10 msec. S/A may constitute a problem, however, if accurate point processing is required, or if GPS receivers are not synchronized. We suggest and test two different methods to monitor satellite frequency offsets due to S/A. S/A modulates GPS carrier frequencies in the range of-2 Hz to +2 Hz over time periods of several minutes. The methods used in this paper to measure the satellite clock dither could be applied by the civilian GPS community to continuously monitor S/A clock dithering. The monitored frequencies may aid high accuracy point positioning applications in a postprocessing mode (Malys and Ortiz 1989), and differential GPS with poorly synchronized receivers (Feigl et al. 1991). 相似文献
8.
The detection of cycle slips in carrier-phase data, outliers in phase rate or in code ranges, or any other type of disorder
in the measurements of the GPS system, is one of the major quality-control problems that needs to be addressed, especially
where GPS is used for real-time applications or for those applications that require continuous and reliable positioning results.
This study is concerned with designing algorithms to detect failures or changes of small magnitude, in order to monitor and
control the quality of GPS measurements for critical real-time and/or deformation applications. In this regard, the statistical
technique known as the cumulative-sum test is described for the detection of abrupt changes in the GPS carrier-phase measurements.
Real GPS data have been used to test and evaluate the algorithm.
Received: 27 August 1996 / Accepted: 26 February 1997 相似文献
9.
Parametric least squares collocation was used in order to study the detection of systematic errors of satellite gradiometer
data. For this purpose, simulated data sets with a priori known systematic errors were produced using ground gravity data
in the very smooth gravity field of the Canadian plains. Experiments carried out at different satellite altitudes showed that
the recovery of bias parameters from the gradiometer “measurements” is possible with high accuracy, especially in the case
of crossing tracks. The mean value of the differences (original minus estimated bias parameters) was relatively large compared
to the standard deviation of the corresponding second-order derivative component at the corresponding height. This mean value
almost vanished when gravity data at ground level were combined with the second-order derivative data set at satellite altitude.
In the case of simultaneous estimation of bias and tilt parameters from ∂2
T/∂z
2“measurements”, the recovery of both parameters agreed very well with the collocation error estimation.
Received: 10 October 1996 / Accepted 25 May 1998 相似文献
10.
GPS技术在变形监测中的应用和发展趋势 总被引：1，自引：0，他引：1
全球定位系统GPS(Global Positiming System),以能够提供连续、实时、无障碍和自动化服务,被广泛应用于导航、测量、勘探等诸多领域。尤其是在测量方面,改变了传统的测量格局,在变形体变形监测领域应用也日趋凸显,由于GPS借助卫星信号传输数据,在实际的监测中也存在一定的局限性。本文首先阐述了变形监测技术,监测数据处理的常规方法;其次介绍了GPS系统应用与变形监测中的优势与不足,并概述了GPS系统应用现状及发展趋势。 相似文献
11.
Assessment of long-range kinematic GPS positioning errors by comparison with airborne laser altimetry and satellite altimetry 总被引：3，自引：0，他引：3
Long-range airborne laser altimetry and laser scanning (LIDAR) or airborne gravity surveys in, for example, polar or oceanic
areas require airborne kinematic GPS baselines of many hundreds of kilometers in length. In such instances, with the complications
of ionospheric biases, it can be a real challenge for traditional differential kinematic GPS software to obtain reasonable
solutions. In this paper, we will describe attempts to validate an implementation of the precise point positioning (PPP) technique
on an aircraft without the use of a local GPS reference station. We will compare PPP solutions with other conventional GPS
solutions, as well as with independent data by comparison of airborne laser data with “ground truth” heights. The comparisons
involve two flights: A July 5, 2003, airborne laser flight line across the North Atlantic from Iceland to Scotland, and a
May 24, 2004, flight in an area of the Arctic Ocean north of Greenland, near-coincident in time and space with the ICESat
satellite laser altimeter. Both of these flights were more than 800 km long. Comparisons between different GPS methods and
four different software packages do not suggest a clear preference for any one, with the heights generally showing decimeter-level
agreement. For the comparison with the independent ICESat- and LIDAR-derived “ground truth” of ocean or sea-ice heights, the
statistics of comparison show a typical fit of around 10 cm RMS in the North Atlantic, and 30 cm in the sea-ice region north
of Greenland. Part of the latter 30 cm error is likely due to errors in the airborne LIDAR measurement and calibration, as
well as errors in the “ground truth” ocean surfaces due to drifting sea-ice. Nevertheless, the potential of the PPP method
for generating 10 cm level kinematic height positioning over long baselines is illustrated. 相似文献
12.
The Doppler effect is the apparent shift in frequency of an electromagnetic signal that is received by an observer moving relative to the source of the signal. The Doppler frequency shift relates directly to the relative speed between the receiver and the transmitter, and has thus been widely used in velocity determination. A GPS receiver-satellite pair is in the Earth’s gravity field and GPS signals travel at the speed of light, hence both Einstein’s special and general relativity theories apply. This paper establishes the relationship between a Doppler shift and a user’s ground velocity by taking both the special and general relativistic effects into consideration. A unified Doppler shift model is developed, which accommodates both the classical Doppler effect and the relativistic Doppler effect under special and general relativities. By identifying the relativistic correction terms in the model, a highly accurate GPS Doppler shift observation equation is presented. It is demonstrated that in the GPS “frequency” or “velocity” domain, the relativistic effect from satellite motion changes the receiver-satellite line-of-sight direction, and the measured Doppler shift has correction terms due to the relativistic effects of the receiver potential difference from the geoid, the orbit eccentricity, and the rotation of the Earth. 相似文献
13.
As technology matures, Real Time Kinematic (RTK) global positioning system (GPS) receivers are providing increased performance
in accuracy, on-the-fly (OTF) initialization times, measurement speed, and latency. Leica's Dozer 2000 machine guidance system
combines an MC1000 GPS sensor, graphic intensive guidance software, a digital terrain model, and a digital site plan. Figure
1 shows the operator's view of the system. The end results is a highly accurate, extremely responsive local navigation system.
Engineers can easily upload design information onto a touch-screen machine guidance personal computer (PC) and greatly reduce
earthmoving costs while simultaneously recording “as-built” inspection data.
The Leica MC1000 machine control sensor is a true 10-Hz, centimeter-level-accuracy, open-architecture GPS sensor specifically
designed for machine guidance and control. At the heart of the MC1000's performance are a very stable oven-controlled oscillator
(3 × 10−11/s short-term stability), a low-power Intel 486-DX4-80 processor, and four user-configurable input/output (I7O) ports. Special
algorithms mitigate the effects of multipath and Selective Availability (SA) while providing centimeter accuracy up to 10
times per second with only 30 milliseconds' latency. The high update rate and low latency are essential for machine guidance
and control.
The MC1000 GPS reference station is capable of outputting RTK and Differential GPS (DGPS) data simultaneously, providing and
entire site with GPS information for machine guidance and control, tracking and dispatching of vehicles, and support of survey
crews.
This article describes how recent advances in technology have combined to produce the Leica Dozer 2000 – a machine guidance
system that is ideal for a wide range of earthmoving and inspection applications. ? 2000 John Wiley & Sons, Inc. 相似文献
14.
15.
In the global positioning system (GPS), code division multiple access (CDMA) signals are used. Because of the known spectral
characteristics of the CDMA signal, continuous wave (CW) interference has a predictable effect on the different pseudo random
noise (PRN) spreading codes (unique to each satellite) depending on the Doppler frequency of the signal. The Doppler frequency
for each signal is also predictable once the receiver position is known. As different satellite signals have different Doppler
frequencies, the effect on the signal quality is also different. In this paper first the effect is studied analytically. The
concept of an “exclusion zone” is defined and analyzed for each satellite. This exclusion zone, where that satellite should
not be used due to interference degradation, is shown to be predictable for each satellite as a function of time. Using this
prediction, the CW interference effect on the positioning quality of the receiver can be mitigated by ignoring the affected
satellites within exclusion zones when performing position evaluation. The threshold beyond which a satellite should be excluded
is then derived by studying the mutual effects of the geometry and the signal quality of that satellite on the positioning
quality. Receiver autonomous integrity monitoring (RAIM) uses redundancy in measurements to perform an internal consistency
check to see if all of the measurements are satisfactory. In this paper this technique is also used to mitigate the effect
of CW interference on the positioning accuracy. Finally it is shown that the prediction of the exclusion zone for each satellite
outperforms the RAIM algorithm in mitigation the effect of the interference when 5 satellites are visible.
An erratum to this article can be found at 相似文献
16.
An acquisition method is proposed which saves processing time and rapidly finds the Global Positioning System (GPS) satellite
with high receiving power. The idea is to combine two or more Coarse/Acquisition (C/A) codes to process acquisition, thus
called “multi-C/A code acquisition method.” The proposed method will change the procedure of conventional Fast Fourier Transform
acquisition slightly, and it has the capabilities to combine with other acquisition methods to perform signal acquisition
simultaneously. In order to show how this multi-C/A code acquisition method may improve the Time To First Fix at the cold
start, the real raw Intermediate Frequency data from a GPS software receiver are used to validate this multi-C/A code acquisition
method. The results show that this method can save at least 23% processing time and it is able to detect the satellite more
rapidly. 相似文献
17.
Impact of Earth radiation pressure on GPS position estimates 总被引：10，自引：8，他引：2
C. J. Rodriguez-Solano U. Hugentobler P. Steigenberger S. Lutz 《Journal of Geodesy》2012,86(5):309-317
GPS satellite orbits available from the International GNSS Service (IGS) show a consistent radial bias of up to several cm
and a particular pattern in the Satellite Laser Ranging (SLR) residuals, which are suggested to be related to radiation pressure
mismodeling. In addition, orbit-related frequencies were identified in geodetic time series such as apparent geocenter motion
and station displacements derived from GPS tracking data. A potential solution to these discrepancies is the inclusion of
Earth radiation pressure (visible and infrared) modeling in the orbit determination process. This is currently not yet considered
by all analysis centers contributing to the IGS final orbits. The acceleration, accounting for Earth radiation and satellite
models, is introduced in this paper in the computation of a global GPS network (around 200 IGS sites) adopting the analysis
strategies from the Center for Orbit Determination in Europe (CODE). Two solutions covering 9 years (2000–2008) with and without
Earth radiation pressure were computed and form the basis for this study. In previous studies, it has been shown that Earth
radiation pressure has a non-negligible effect on the GPS orbits, mainly in the radial component. In this paper, the effect
on the along-track and cross-track components is studied in more detail. Also in this paper, it is shown that Earth radiation
pressure leads to a change in the estimates of GPS ground station positions, which is systematic over large regions of the
Earth. This observed “deformation” of the Earth is towards North–South and with large scale patterns that repeat six times
per GPS draconitic year (350 days), reaching a magnitude of up to 1 mm. The impact of Earth radiation pressure on the geocenter
and length of day estimates was also investigated, but the effect is found to be less significant as compared to the orbits
and position estimates. 相似文献
18.
Lars E. Sjöberg 《Journal of Geodesy》1991,65(4):209-217
In October 1987 a four day satellite GPS campaign was performed over the Åland archipelago to test the possibility of connecting the Swedish and Finnish national height systems. This paper summarizes the gained experiences using 5 WM 101 GPS receivers and the PoPS software.The computing results for the connection between the two height systems are considerably dependent on the choice of geoidal undulation model and systematic error parameter model. Using the NKG Scandinavian geoid 1989, which is probably the most accurate geoid available for the region, and a bias and tilt parameter model the difference between the Swedish RH70 system and the Finnish N60 system is estimated to 11.4 ± 4.0 cm. An independent check is provided by two connecting border bench marks in northern Scandinavia yielding the difference 19.2 ± 4.2 cm. In view of that merely single frequency GPS receivers were used together with the PoPS software, we consider this result most satisfactory. 相似文献
19.
P. Schwintzer C. Reigber A. Bode Z. Kang S. Y. Zhu F.-H. Massmann J. C. Raimondo R. Biancale G. Balmino J. M. Lemoine B. Moynot J. C. Marty F. Barlier Y. Boudon 《Journal of Geodesy》1997,71(4):189-208
Summary. GFZ Potsdam and GRGS Toulouse/Grasse jointly developed a new pair of global models of the Earth's gravity field to satisfy
the requirements of the recent and future geodetic and altimeter satellite missions. A precise gravity model is a prerequisite
for precise satellite orbit restitution, tracking station positioning and altimeter data reduction. According to different
applications envisaged, the new model exists in two parallel versions: the first one being derived exclusively from satellite
tracking data acquired on 34 satellites, the second one further incorporating satellite altimeter data over the oceans and
terrestrial gravity data. The most recent “satellite-only” gravity model is labelled GRIM4-S4 and the “combined” gravity model
GRIM4-C4. The models are solutions in spherical harmonics and have a resolution up to degree and order 60 plus a few resonance
terms in the case of GRIM4-S4, and up to degree/order 72 in the case of GRIM4-C4, corresponding to a spatial resolution of
555 km at the Earth's surface. The gravitational coefficients were estimated in a rigorous least squares adjustment simultaneously
with ocean tidal terms and tracking station position parameters, so that each gravity model is associated with a consistent
ocean tide model and a terrestrial reference frame built up by over 300 optical, laser and Doppler tracking stations. Comprehensive
quality tests with external data and models, and test arc computations over a wide range of satellites have demonstrated the
state-of-the-art capabilities of both solutions in long-wavelength geoid representation and in precise orbit computation.
Received 1 February 1996; Accepted 17 July 1996 相似文献
20.
Pascal Willis 《GPS Solutions》1999,3(2):66-68
GLONASS is a Russian military navigation satellite system. Even if the constellation is far from being operational, a large
community is potentially interested in using its signal in combination with GPS to improve availability, integrity, or precision.
The goal of this article is to present the international GLONASS campaign, named IGEX-98, which is really the first attempt
to obtain precise GLONASS orbits for geodetic applications. A world-wide network of GLONASS receivers has been deployed and
is still operational. Several analysis centers process the GLONASS data on a regular basis in the same way it is done for
GPS within the International GPS Service. ? 1999 John Wiley & Sons, Inc. 相似文献