共查询到20条相似文献,搜索用时 31 毫秒
1.
GPS卫星钟的特性与预报研究 总被引:1,自引:0,他引:1
经实验分析发现:GPS卫星钟差的预报精度与卫星的种类密切相关,最近发射的BLOCK ⅡR和BLOCKIIR-M类卫星比以往的BLOCK ⅡA类卫星要更加稳定,其卫星钟差的预报精度明显较高。直接利用IGS超快速产品和线性模型预报后6小时的卫星钟差,精度在0.5纳秒水平;但一些BLOCK ⅡA类卫星是不稳定的,通过对其预报残差的分析发现:同一颗卫星每天在相同时段用相同的模型去预报其卫星钟差,预报所得的残差呈周期性变化,并且这种周期性变化并不完全重合,还具有一定的随机性。依据这一特性本文构建了一个新的预报模型来实时预报GPS卫星钟差。该模型不仅能预报卫星钟差的总体变化趋势,还能预报残差的周期性变化以及随机项的变化,因此精度更高。预报结果均与IGS发布的最终产品相比,实验显示利用该方法实时预报GPS卫星钟差,预报精度可达0.5纳秒水平。 相似文献
2.
A simplified yaw-attitude model for eclipsing GPS satellites 总被引:11,自引:2,他引:9
J. Kouba 《GPS Solutions》2009,13(1):1-12
A simplified yaw-attitude modeling, consistent with Bar-Sever (1996), has been implemented and tested in the NRCan PPP software.
For Block IIR GPS satellite it is possible to model yaw-attitude control during eclipsing periods by using the constant hardware
yaw rate of 0.20°/s. The Block IIR satellites maintain the nominal yaw attitude even during a shadow crossing (Y. E. Bar-Sever,
private communication, 2007), except for the noon and shadow midnight turn maneuvers, both of which can be modeled and last
up to 15 min. Thus, for Block IIR satellites it is possible to maintain continuous satellite clock estimation even during
eclipsing periods. For the Block II/IIA satellites, it is possible to model satisfactorily the noon turns and also shadow
crossing, thanks to the permanent positive yaw bias of 0.5°, implemented in November 1995. However, in order to model the
Block II/IIA shadow crossings, satellite specific yaw rates should be used, either solved for or averaged yaw-rate solutions.
These yaw rates as estimated by the Jet Propulsion Laboratory (JPL) can differ significantly from the nominal hardware values.
The Block II/IIA post-shadow recovery periods, which last about 30 min, should be considered uncertain and cannot be properly
modeled. Data from post-shadow recovery periods should, therefore, not be used in precise global GPS analyses (Bar-Sever 1996). For high-precision applications, it is essential that users implement a yaw-attitude model, which is consistent with the
generation of the satellite clocks. Initial testing and analyses, based on the IGS and AC Final orbits and clocks have revealed
that during eclipsing periods, significant inconsistencies in yaw-attitude modeling still exist amongst the IGS Analyses Centers,
which contribute to the errors of the IGS Final clock combinations. 相似文献
3.
A technique for obtaining clock measurements from individual GNSS satellites at short time intervals is presented. The methodology developed in this study allows for accurate satellite clock stability analysis without an ultra-stable clock at the ground receiver. Variations in the carrier phase caused by the satellite clock are isolated using a combination of common GNSS carrier-phase processing techniques. Furthermore, the white phase variations caused by the thermal noise of the collection and processing equipment are statistically modeled and removed, allowing for analysis of clock performance at subsecond intervals. Allan deviation analyses of signals collected from GPS and GLONASS satellites reveal distinct intervals of clock noise for timescales less than 100 s. The clock data collected from GPS Block IIA, IIR, IIR-M, and GLONASS satellites reveal similar stability performance at time periods greater than 20 s. The GLONASS clock stability in the 0.6–10 s range, however, is significantly worse than GPS. Applications that rely on ultra-stable clock behavior from the GLONASS satellites at these timescales may therefore require high-rate corrections to estimate and remove oscillator-based errors in the carrier phase. 相似文献
4.
Improved relativistic transformations in GPS 总被引:1,自引:1,他引:0
For GPS satellite clocks, a nominal (hardware) frequency offset and a conventional periodic relativistic correction derived as a dot product of the satellite position and velocity vectors, are used to compensate the relativistic effects. The conventional hardware clock rate offset of 38,575.008 ns/day corresponds to a nominal orbit semi-major axis of about 26,561,400 m. For some of the GPS satellites, the departures from the nominal semi-major axis can cause an apparent clock rate up to 10 ns/day. GPS orbit perturbations, together with the earth gravity field oblateness, which is largely responsible for the orbit perturbations, cause the standard GPS relativistic transformations to depart from the rigorous relativity transformation by up to 0.2 ns/day. In addition, the conventional periodic relativistic correction exhibits periodic errors with amplitudes of about 0.1 and 0.2 ns, with periods of about 6 h and 14 days, respectively. Using an analytical integration of the gravity oblateness term (J2), a simple analytical approximation was derived for the apparent clock rate and the 6-h periodic errors of the standard GPS gravity correction. For daily linear representations of GPS satellite clocks, the improved relativistic formula was found to agree with the precise numerical integration of the GPS relativistic effects within about 0.015 ns. For most of the Block IIR satellites, the 6-h periodical errors of the GPS conventional relativistic correction are already detectable in the recent IGS final clock combinations. 相似文献
5.
J. Kouba 《GPS Solutions》2002,5(4):1-9
Since Selective Availability was permanently switched off on 7 May 2000, most of the GPS satellite clocks have been well behaved.
During a 24-h period precise satellite clock solutions, corrected for GPS conventional relativistic corrections, follow straight
lines within a few nanoseconds. The linear clock fit RMS for the best satellite clocks are well below the 1-ns level, which
is consistent with the nominal stability of the GPS frequency standards. Typically, the GPS satellite clocks show an Allan
variance at or below one part in 1011/100 s for the Cesium frequency standards and a few parts in 1012/100 s for the Rubidium frequency standards. These results correspond to clock RMSs for 15-min sampling at or below 3 and
0.3 ns, respectively. This already confirms experimentally that the conventional periodic relativity correction of the GPS
system, also adopted for all the IGS clock solution products, is precise and correct to 0.6 ns or better. To establish the
precision limits of the GPS conventional relativity treatment, the relativistic time transformations of GPS satellite frequency
and clocks are critically reviewed, taking into account all the contributions larger than the 10−18 (or 0.001 ns). The conventional GPS relativity treatment was found to be accurate, i. e., correctly modeling the actual relativistic
frequency (clock rate) effects of GPS satellites at about the 10−14 level. However, it is also affected by small periodic errors of the same magnitude. The integration of these small periodic
frequency relativistic errors gives the approximation errors of the conventional periodic relativistic clock correction with
amplitudes of about 0.1 ns and a predominant period equal to a half of the orbital period (∼ 6 h). These approximation errors
of the conventional GPS relativistic clock correction are at about the same level as the current precision of the IGS clock
solutions. ? 2002 Wiley Periodicals, Inc. 相似文献
6.
星载原子钟作为导航卫星上维持时间尺度的关键载荷,其性能会对用户进行导航、定位与授时的精度带来影响。介绍了原子钟评估常用的三个指标(频率准确度、飘移率和稳定度)的定义及计算方法,利用事后卫星精密钟差数据,开展了全球卫星导航系统(global navigation satellite system,GNSS)星载原子钟性能评估,分析了GNSS星载原子钟特性。结果表明,GPS(global position system)BLOCKIIF星载铷钟与Galileo星载氢钟综合性能最优;北斗系统中地球轨道卫星与倾斜同步轨道卫星星载原子钟天稳定度达到2~4×10-14量级,与BLOCK IIR卫星精度相当;频率准确度达到1~4×10-11量级;频率漂移率达到10-14量级。 相似文献
7.
Oliver Montenbruck Urs Hugentobler Rolf Dach Peter Steigenberger André Hauschild 《GPS Solutions》2012,16(3):303-313
The Block IIF satellites feature a new generation of high-quality rubidium clocks for time and frequency keeping and are the first GPS satellites transmitting operational navigation signals on three distinct frequencies. We investigate apparent clock offset variations for the Block IIF-1 (SVN62) spacecraft that have been identified in L1/L2 clock solutions as well as the L1/L5-minus-L1/L2 clock difference. With peak-to-peak amplitudes of 10?C40?cm, these variations are of relevance for future precision point positioning applications and ionospheric analyses. A proper characterization and understanding is required to fully benefit from the quality of the new signals and clocks. The analysis covers a period of 8?months following the routine payload activation and is based on GPS orbit and clock products generated by the CODE analysis center of the International GNSS Service (IGS) as well as triple-frequency observations collected with the CONGO network. Based on a harmonic analysis, empirical models are presented that describe the sub-daily variation of the clock offset and the inter-frequency clock difference. These contribute to a better clock predictability at timescales of several hours and enable a consistent use of L1/L2 clock products in L1/L5-based positioning. 相似文献
8.
This study evaluates the quality of GPS radio occultation (RO) atmospheric excess phase data derived with single- and double-difference
processing algorithms. A spectral analysis of 1 s GPS clock estimates indicates that a sampling interval of 1 s is necessary
to adequately remove the GPS clock error with single-difference processing. One week (May 2–8, 2009) of COSMIC/FORMOSAT-3
data are analyzed in a post-processed mode with four different processing strategies: (1) double-differencing with 1 s GPS
ground data, (2) single-differencing with 30 s GPS clock estimates (standard COSMIC Data Analysis and Archival Center product),
(3) single-differencing with 5 s GPS clocks, and (4) single-differencing with 1 s GPS clocks. Analyses of a common set of
5,596 RO profiles show that the neutral atmospheric bending angles and refractivities derived from single-difference processing
with 1 s GPS clocks are the highest quality. The random noise of neutral atmospheric bending angles between 60 and 80 km heights
is about 1.50e−6 rad for the single-difference cases and 1.74e−6 rad for double-differencing. An analysis of pairs of collocated
soundings also shows that bending angles derived from single-differencing with 1 s GPS clocks are more consistent than with
the other processing strategies. Additionally, the standard deviation of the differences between RO and high-resolution European
Center for Medium range Weather Forecasting (ECMWF) refractivity profiles at 30 km height is 0.60% for single-differencing
with 1 and 5 s GPS clocks, 0.68% for single-differencing with 30 s clocks, and 0.66% for double-differencing. A GPS clock-sampling
interval of 1 s or less is required for single- and zero-difference processing to achieve the highest quality excess atmospheric
phase data for RO applications. 相似文献
9.
本文提出了一种GPS卫星导航增强系统技术性能分析方法,即利用IGS提供的高精度GPS星历、卫星钟差数据和电离层数据作为外符和检测标准,检验增强系统提供的卫星星历改正数据、卫星钟差改正数据和电离层改正数据的精度。通过实测数据分析表明,我国GPS卫星导航增强系统目前的服务性能与国外同类系统具有一定的差距,主要的技术薄弱环节在于GPS卫星的精密定轨与钟差解算技术。 相似文献
10.
A computationally efficient approach for estimating high-rate satellite clock corrections in realtime 总被引:9,自引:5,他引:4
Realtime satellite clock corrections are usually estimated using undifferenced phase and range observations from a global
network. Because a large number of ambiguity parameters must be estimated, the computation is time-consuming. Consequently,
only a sparse global network of limited number of stations is processed by most IGS Realtime Analysis Centers with an update
rate of 5 s. In addition, it is very desirable to build the capability to simultaneously estimate clock corrections for multi-GNSS
constellations. Although the estimation can be sped up by epoch-differenced observations that eliminate ambiguities, the derived
clocks can contain a satellite-specific bias that diminishes the contribution of range observations. We introduce a computationally
efficient approach for realtime clock estimation. Both the epoch-differenced phase and undifferenced range observations are
used together to estimate the epoch-differenced satellite clocks and the initial clock bias for each satellite and receiver.
The biased clock corrections accumulated from the estimated epoch-differenced clocks are then aligned with the estimated clock
biases and provided as the final clock corrections to users. The algorithm is incorporated into the EPOS-RT software developed
at GFZ (GeoForschungsZentrum) and experimentally validated with the IGS global network. The comparison with the GFZ rapid
products shows that the accuracy of the clock estimation with the new approach is comparable with that of the undifferenced
approach, whereas the computation time is reduced to one-tenth. As a result, estimation of high-rate satellite clocks from
a large reference network and tracking satellites of multi-GNSS constellations becomes achievable. 相似文献
11.
New IGS Station and Satellite Clock Combination 总被引:3,自引:5,他引:3
Following the principles set forth in the Position Paper #3 at the 1998 Darmstadt Analysis Center (AC) Workshop on the new
International GPS Service (IGS) International Terrestrial Reference Frame (ITRF) realization and discussions at the 1999 La
Jolla AC workshop, a new clock combination program was developed. The program allows for the input of both SP3 and the new
clock (RINEX) format (ftp://igsch.jpl.nasa.gov//igscb/data/format/rinex_clock.txt). The main motivation for this new development
is the realization of the goals of the IGS/BIPM timing project. Besides this there is a genuine interest in station clocks
and a need for a higher sampling rate of the IGS clocks (currently limited to 15 min due to the SP3 format). The inclusion
of station clocks should also allow for a better alignment of the individual AC solutions and should enable the realization
of a stable GPS time-scale.
For each input AC clock solution the new clock combination solves and corrects for reference clock errors/instabilities as
well as satellite/station biases, geocenter and station/satellite orbit errors. External station clock calibrations and/or
constraints, such as those resulting from the IGS/BIPM timing pilot project, can be introduced via a subset of the fiducial
timing station set, to facilitate a precise and consistent IGS UTC realization for both station and satellite combined clock
solutions. Furthermore, the new clock combination process enforces strict strict conformity and consistency with the current
and future IGS standards.
The new clock combination maintains orbit/clock consistency at millimeter level, which is comparable to the best AC orbit/clock
solutions. This is demonstrated by static GIPSY precise point positioning tests using GPS week 0995 data for stations in both
Northern and Southern Hemispheres and similar tests with the Bernese software using more recent data from GPS week 1081. ?
2001 John Wiley & Sons, Inc. 相似文献
12.
Short-term analysis of GNSS clocks 总被引:6,自引:6,他引:0
A characterization of the short-term stability of the atomic frequency standards onboard GNSS satellites is presented. Clock performance is evaluated using two different methods. The first method derives the temporal variation of the satellite’s clock from a polynomial fit through 1-way carrier-phase measurements from a receiver directly connected to a high-precision atomic frequency standard. Alternatively, three-way measurements using inter-station single differences of a second satellite from a neighboring station are used if the receiver’s clock stability at the station tracking the satellite of interest is not sufficient. The second method is a Kalman-filter-based clock estimation based on dual-frequency pseudorange and carrier-phase measurements from a small global or regional tracking network. Both methods are introduced and their respective advantages and disadvantages are discussed. The analysis section presents a characterization of GPS, GLONASS, GIOVE, Galileo IOV, QZSS, and COMPASS clocks based on these two methods. Special focus has been set on the frequency standards of new generation satellites like GPS Block IIF, QZSS, and IOV as well as the Chinese COMPASS/BeiDou-2 system. The analysis shows results for the Allan deviation covering averaging intervals from 1 to 1,000 s, which is of special interest for real-time PPP and other high-rate applications like processing of radio-occultation measurements. The clock interpolation errors for different sampling rates are evaluated for different types of clocks and their effect on PPP is discussed. 相似文献
13.
随着全球卫星导航系统的发展,GNSS卫星发播多频观测量已成必然趋势。然而,目前IGS分析中心依然使用双频观测量的策略进行轨道、钟差等产品的解算,并没有顾及额外频点观测量对定轨产品带来的效益。本文使用两个双频无电离层组合(IF)作为观测模型,研究第三频点观测量对轨道、钟差及测站位置精度的改善。在观测方程中将卫星端的相位偏差分成时变和时不变分量,通过对两个IF组合的观测方程进行参数重组,推导了与IGS钟差产品基准一致的满秩观测模型。基于超宽巷、宽巷和窄巷双差模糊度构建策略,给出了三频观测量的模糊度固定方法。首先以12颗GPS Block IIF卫星为例,在两种测站布局情况下进行L1/L2 IF双频定轨(S1)、L1/L5 IF双频定轨(S2)、L1/L2和L1/L5两个IF组合的三频定轨(S3)试验。结果表明S3方案最优,测站均匀、不均匀情况下轨道结果S3相较S1分别改善10%以内、10%左右,钟差的RMS略有改善,STD分别改善6.4%、10.0%,而S3相较S2的改善幅度更小,改善百分比基本在5%以内。随后进行了BDS单系统定轨,并使用激光检核轨道,表明三频定轨较B1/B3定轨结果改善显著,但是较B1/B2方案结果改善微弱,可能的原因是天线相位中心误差改正值不准确。 相似文献
14.
Ziqian Wu Shanshi Zhou Xiaogong Hu Li Liu Tao Shuai Yonghui Xie Chengpan Tang Junyang Pan Lingfeng Zhu Zhiqiao Chang 《GPS Solutions》2018,22(2):43
Various types of onboard atomic clocks such as rubidium, cesium and hydrogen have different frequency accuracies and frequency drift rate characteristics. A passive hydrogen maser (PHM) has the advantage of low-frequency drift over a long period, which is suitable for long-term autonomous satellite time keeping. The third generation of Beidou Satellite Navigation System (BDS3) is equipped with PHMs which have been independently developed by China for their IGSO and MEO experimental satellites. Including Galileo, it is the second global satellite navigation system that uses PHM as a frequency standard for navigation signals. We briefly introduce the PHM design at the Shanghai Astronomical Observatory (SHAO) and detailed performance evaluation of in-orbit PHMs. Using the high-precision clock values obtained by satellite-ground and inter-satellite measurement and communication systems, we analyze the frequency stability, clock prediction accuracy and clock rate variation characteristics of the BDS3 experimental satellites. The results show that the in-orbit PHM frequency stability of the BDS3 is approximately 6 × 10?15 at 1-day intervals, which is better than those of other types of onboard atomic clocks. The BDS3 PHM 2-, 10-h and 7-day clock prediction precision values are 0.26, 0.4 and 2.2 ns, respectively, which are better than those of the BDS3 rubidium clock and most of the GPS Block IIF and Galileo clocks. The BDS3 PHM 15-day clock rate variation is ? 1.83 × 10?14 s/s, which indicates an extremely small frequency drift. The 15-day long-term stability results show that the BDS3 PHM in-orbit stability is roughly the same as the ground performance test. The PHM is expected to provide a highly stable time and frequency standard in the autonomous navigation case. 相似文献
15.
Recent studies have shown the capabilities of Global Positioning System (GPS) carrier phases for frequency transfer based
on the observations from geodetic GPS receivers driven by stable atomic clocks. This kind of receiver configuration is the
kind primarily used within the framework of the International GPS Service (IGS). The International GPS Service/Bureau International
des Poids et Mesures (IGS/BIPM) pilot project aims at taking advantage of these GPS receivers to enlarge the network of Time
Laboratories contributing to the realization of the International Atomic Time (TAI).
In this article, we outline the theory necessary to describe the abilities and limitations of time and frequency transfer
using the GPS code and carrier phase observations. We report on several onsite tests and evaluate the present setup of our
12-channel IGS receiver (BRUS), which uses a hydrogen maser as an external frequency reference, to contribute to the IGS/BIPM
pilot project.
In the initial experimental setup, the receivers had a common external frequency reference; in the second setup, separate
external frequency references were used. Independent external clock monitoring provided the necessary information to validate
the results. Using two receivers with a common frequency reference and connected to the same antenna, a zero baseline, we
were able to use the carrier phase data to derive a frequency stability of 6 × 10−16 for averaging times of one day. The main limitation in the technique originates from small ambient temperature variations
of a few degrees Celsius. While these temperature variations have no effect on the functioning of the GPS receiver within
the IGS network, they reduce the capacities of the frequency transfer results based on the carrier phase data. We demonstrate
that the synchronization offset at the initial measurement epoch can be estimated from a combined use of the code and carrier
phase observations. In our test, the discontinuity between two consecutive days was about 140 ps. ? 1999 John Wiley & Sons,
Inc. 相似文献
16.
Real-time clock offset prediction with an improved model 总被引:5,自引:3,他引:2
The GPS orbit precision of the IGS ultra-rapid predicted (IGU-P) products has been remarkably improved since 2007. However, the satellite clock offsets of the IGU-P products have not shown sufficient high-quality prediction to achieve sub-decimeter precision in real-time precise point positioning (RTPPP), being at the level of 1–3 ns (30–90 cm) RMS in recent years. An improved prediction model for satellite clocks is proposed in order to enhance the precision of predicted clock offsets. First, the proposed prediction model adds a few cyclic terms to absorb the periodic effects, and a time adaptive function is used to adjust the weight of the observation in the prediction model. Second, initial deviations of the predictions are reduced by using a recomputed constant term. The simulation results have shown that the proposed prediction model can give a better performance than the IGU-P clock products and can achieve precision better than 0.55 ns (16.5 cm) in real-time predictions. In addition, the RTPPP method was chosen to test the efficiency of the new model for real-time static and kinematic positioning. The numerical examples using the data set of 140 IGS stations show that the static RTPPP precision based on the proposed clock model has been improved about 22.8 and 41.5 % in the east and height components compared to the IGU-P clock products, while the precisions in the north components are the equal. The kinematic example using three IGS stations shows that the kinematic RTPPP precision based on the proposed clock model has improved about 30, 72 and 44 % in the east, north and height components. 相似文献
17.
18.
针对北斗在轨卫星Rb原子钟2013年的实测数据,采用二次多项式拟合得到BDS卫星钟差模型,采用哈达玛总方差公式计算了北斗卫星钟的短期频率稳定度指标,进而分析了北斗在轨卫星钟特性指标的变化规律。通过实例计算,揭示了BDS不同在轨卫星钟的相位、频率、频漂及残差指标的变化规律;计算得出BDS卫星钟万秒频率稳定度维持在10-13量级左右,其中GEO卫星钟的稳定度相对较差,4号和8号卫星在运行期间出现跳变,跳变之后稳定性得到提高,其他在轨卫星钟稳定度变化趋势则相对平稳。 相似文献
19.
Due to the limited frequency stability and poor accuracy of typical quartz oscillators built-in GNSS receivers, an additional receiver clock error has to be estimated in addition to the coordinates. This leads to several drawbacks especially in kinematic applications: At least four satellites in view are needed for navigation, high correlations between the clock estimates and the up-coordinates. This situation can be improved distinctly when connecting atomic clocks to GNSS receivers and modeling their behavior in a physically meaningful way (receiver clock modeling). Recent developments in miniaturizing atomic clocks result in so-called chip-scale atomic clocks and open up the possibility of using stable atomic clocks in GNSS navigation. We present two different methods of receiver clock modeling, namely in an extended Kalman filter and a sequential least-squares adjustment for code-based GNSS navigation using three different miniaturized atomic clocks. Using the data of several kinematic test drives, the benefits of clock modeling for GPS navigation solutions are assessed: decrease in the noise of the up-coordinates by up to 69 % to 20 cm level, decrease in minimal detectable biases by 16 %, and elimination of spikes and subsequently decrease in large position errors (35 %). Hence, a more robust position is obtained. Additionally, artificial partial satellite outages are generated to demonstrate position solutions with only three satellites in view. 相似文献
20.
Progress in Carrier Phase Time Transfer 总被引:1,自引:0,他引:1
Jim Ray Felicitas Arias Gérard Petit Tim Springer Thomas Schildknecht Jon Clarke Jan Johansson 《GPS Solutions》2001,4(4):47-54
The progress of the joint Pilot Project for time transfer, formed by the International GPS Service (IGS) and the Bureal International
des Poids et Mesures (BIPM), was recently reviewed. Three notable milestones were set. (1) The IGS will implement, at least
in a test mode, an internally realized time scale based on an integration of combined frequency standards within the IGS network.
This will eventually become the reference time scale for all IGS clock products (instead of the current GPS broadcast time).
(2) A new procedure for combined receiver and satellite clock products will be implemented officially in November 2000. Receiver
clocks are an entirely new product of the IGS. (3) The BIPM will coordinate an effort to calibrate all Ashtech Z12-T (and
possibly other) receivers suitable for time transfer applications, either differentially or absolutely. Progress reports will
be presented publicly in the spring 2001. ? 2001 John Wiley & Sons, Inc. 相似文献