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1.
We consider disturbances of total electron content (TEC) of the high-latitude ionosphere provided by the GPS global navigation satellite system before and during the magnetic storm on April 5, 2010. Simultaneously, we examine magnetic data from all available magnetometer arrays in the northern hemisphere, augmented with data from scanning photometers and riometers. The substorm onset, during both non-storm and storm periods, is found to cause significant enhancement of TEC scintillations characterized by the TEC time derivative dTEC. Comparison of 2D maps of the spectral power of magnetic fluctuations in the Pc5 band (1–10 mHz) and dTEC during substorms shows a good spatial and temporal correspondence between them. Both magnetic and ionospheric fluctuations tend to concentrate inside the auroral oval, the boundaries of which are determined from the OVATION model. The time–space evolution of TEC scintillations is rather similar to that of ultra-low-frequency magnetic fluctuations, but not to that of the ionospheric electrojet. GPS signal phase slips, resulting in non-physical TEC jumps (>1 TECu/min), occur predominantly inside the auroral oval and in the vicinity of its equatorward boundary. 相似文献
2.
电离层参量的提取是开展电离层研究的基础,而数据同化技术则是获取电离层参量的一种重要手段。以NeQuick模型的输出作为背景场,Kalman滤波作为同化算法,利用数据同化技术实现区域电离层TEC重构,结果表明,数据同化方法重构的倾斜总电子含量（TEC）和垂直TEC与实测值较为一致。相比NeQuick模型及全球电离层地图（GIM）数据,数据同化方法重构得到的TEC的平均误差和标准差均有明显的降低,实测数据验证了数据同化技术在区域TEC重构中的精度和可靠性。 相似文献
3.
4.
Assessment of ECMWF-derived tropospheric delay models within the EUREF Permanent Network 总被引：1，自引：0，他引：1
The Global Positioning System (GPS) observations from the EUREF Permanent Network (EPN) are routinely analyzed by the EPN
analysis centers using a tropospheric delay modeling based on standard pressure values, the Niell Mapping Functions (NMF),
a cutoff angle of 3° and down-weighting of low elevation observations. We investigate the impact on EPN station heights and
Zenith Total Delay (ZTD) estimates when changing to improved models recommended in the updated 2003 International Earth Rotation
and Reference Systems Service (IERS) Conventions, which are the Vienna Mapping Functions 1 (VMF1) and zenith hydrostatic delays
derived from numerical weather models, or the empirical Global Mapping Functions (GMF) and the empirical Global Pressure and
Temperature (GPT) model. A 1-year Global Positioning System (GPS) data set of 50 regionally distributed EPN/IGS (International
GNSS Service) stations is processed. The GPS analysis with cutoff elevation angles of 3, 5, and 10° revealed that changing
to the new recommended models introduces biases in station heights in the northern part of Europe by 2–3 mm if the cutoff
is lower than 5°. However, since large weather changes at synoptic time scales are not accounted for in the empirical models,
repeatability of height and ZTD time series are improved with the use of a priori Zenith Hydrostatic Delays (ZHDs) derived
from numerical weather models and VMF1. With a cutoff angle of 3°, the repeatability of station heights in the northern part
of Europe is improved by 3–4 mm. 相似文献
5.
The inverse distance weighted model (IDWM) represents a geo-spatial interpolation technique used for estimation of ionospheric
vertical delays at the ionospheric grid points (IGPs) and user ionospheric pierce points (IPPs). The GPS Aided Geo Augmented
Navigation (GAGAN) system is planned for air-navigation over the Indian service region using a space based augmentation. One
of the main needs for GAGAN is to develop a suitable grid-based ionospheric model for estimating the vertical delay and its
error bound, i.e., grid ionospheric vertical error (GIVE) at all the IGPs covering the Indian subcontinent. Dual frequency
GPS receiver data obtained from 17 total electron content (TEC) stations are considered in the analysis. For a typical IGP
(25°N, 75°E), variations in the GIVE for a few days of quiet ionosphere are presented. For a quiet and magnetically moderate
day, the mean and standard deviations of the user IPP (UIPP) estimation error and the mean GIVE are presented using the IDWM
with Klobuchar, Junkins and bilinear models. 相似文献
6.
Single layer ionosphere models are frequently used for ionospheric modeling and estimation using GPS measurements from a network of GPS reference stations. However, the accuracies of single layer models are inherently constrained by the assumption that the ionospheric electrons are concentrated in a thin shell located at an altitude of about 350 km above Earths surface. This assumption is only an approximation to the physical truth because the electrons are distributed in the entire ionosphere region approximately from 50 to 1,000 km. To provide instantaneous ionospheric corrections for the real-time GPS positioning applications, the ionospheric corrections need to be predicted in advance to eliminate the latency caused by the correction computation. This paper will investigate ionospheric total electron content (TEC) predictions using a multiple-layer tomographic method for ionospheric modeling over a local area GPS reference network. The data analysis focuses on the accuracy evaluation of short-term (5 min in this study) TEC predictions. The results have indicated that the obtainable TEC prediction accuracy is at a level of about 2.8 TECU in the zenith direction and 95% of the total electron content can be recovered using the proposed tomography-based ionosphere model. 相似文献
7.
DGPS services are provided in support of land and marine applications by many government agencies worldwide. Horizontal positioning accuracies in the order of several metres are typically achieved for these systems. Under high levels of ionospheric activity, however, significant degradations in DGPS positioning accuracies can occur. In particular, gradients of up to 50 ppm are associated with a feature known as storm-enhanced density (SED). This feature is a localized enhancement of total electron content (TEC) extending north through the mid-latitudes into the polar region. DGPS positioning errors of 20 m or more can persist for hours during such events. In this paper, archived IGS data from GPS reference stations are used to derive high-resolution TEC maps for two SED events. The impact of SED effects on DGPS horizontal positioning accuracies is then quantified using data from select IGS reference stations in North America and Europe. Results indicate that positioning accuracies may be degraded by factors as large as 10–20 during such events. 相似文献
8.
不同Klobuchar模型参数的性能比较 总被引：3，自引：1，他引：2
对于GPS单频用户而言,电离层延迟是最重要的误差来源之一。GPS系统使用Klobuchar模型对电离层延迟进行改正,其改正数从370组常数中选取。目前全球分布的GPS测站可以获得高精度的全球电离层监测结果,GPS为什么不发播采用实测数据计算得到的Klobuchar模型参数呢？本文针对这一问题进行分析。首先对欧洲定轨中心CODE提供的全球电离层图GIM预报COPG电离层进行精度评估,然后根据COPG电离层进行Klobuchar模型参数拟合并利用IGS提供的事后高精度电离层图进行精度分析,最后将不同的电离层模型参数应用于单点定位以评估其对单频用户的影响。分析结果表明：受8参数的Klobuchar模型本身结构限制,采用全球实测数据计算的电离层模型参数与导航电文中发播的电离层模型精度相当,为55%左右。而仅采用地磁纬度45oS以北的数据拟合得到的模型参数,其电离层改正精度有明显提升,可达65%左右,但其对单频用户定位精度改善不明显。本文研究结果为我国全球电离层建模提供参考。 相似文献
9.
Storm-enhanced density (SED) is a geomagnetic storm phenomenon, characterized by a plume of enhanced total electron content (TEC) that initially moves poleward and sunward extending out from a larger region of enhanced TEC in the mid-latitudes. SED is associated with extreme mid-latitude space weather effects. Sharp gradients in the TEC are found along the borders of SED plumes and at the boundaries of the larger TEC region (the base of the plume). These large TEC gradients can cause significant errors in DGPS and WADGPS positioning and can result in serious consequences for applications such as railway control, highway traffic management, emergency response, commercial aviation and marine navigation, all of which require high precision, real-time positioning. Data from the global IGS network of GPS receivers have enabled the spatial and temporal visualization of these SED plumes, allowing ionospheric researchers to study this phenomenon and investigate the potential for developing prediction techniques and real-time warning systems. GPS TEC maps provided by analysis of the data from the IGS network have now been widely disseminated throughout the atmospheric research community and have become one of the standard means of studying the effects of geomagnetic storms on the ionosphere. These maps have enabled researchers to identify that the SED phenomenon occurs globally, is associated with large TEC gradients (at times greater than 100 TEC units per degree latitude), and is a magnetically conjugate phenomenon. This paper reports on the recent advances in our understanding of the SED phenomenon enabled by GPS observations. 相似文献
10.
The FORMOSAT-3/COSMIC mission has provided ample ionospheric electron density profiles retrieved from the global positioning
system radio occultation technique. Currently, there can be more than 2,000 electron density profiles acquired per day covering
the global ionosphere from altitude 90 to 800 km. Utilizing the advantage of such a complete coverage, we statistically analyze
how the ionospheric electron parameters NmF2, hmF2, and TEC respond to the geomagnetic index Dst for different magnetic latitudes
and magnetic local time (MLT) and on quiet and storm times. A data set of 24 months is used for this study, in which most
of the results focus on the low-latitude dayside regions. The results indicate that, in general, NmF2, hmF2, and TEC decrease
as Dst increases at all seasons. Only during the sudden commencement phase (SSC) of storm events, NmF2 and TEC appear to increase
as Dst increases. 相似文献
11.
Ambiguity resolution in precise point positioning with hourly data 总被引：19，自引：7，他引：12
Precise point positioning (PPP) has become a powerful tool for the scientific analysis of Global Positioning System (GPS)
measurements. Until recently, ambiguity resolution at a single station in PPP has been considered difficult, due to the receiver-
and satellite-dependent uncalibrated hardware delays (UHD). However, recent studies show that if these UHD can be determined
accurately in advance within a network of stations, then ambiguity resolution at a single station becomes possible. In this
study, the method proposed by Ge et al. J Geod 82(7):389–399, 2007 is adopted with a refinement in which only one single-difference narrow-lane UHD between a pair of satellites is determined
within each full pass over a regional network. This study uses the EUREF (European Reference Frame) Permanent Network (EPN)
to determine the UHD from Day 245 to 251 in 2007. Then 12 International GNSS Service stations inside the EPN and 15 outside
the EPN are used to conduct ambiguity resolution in hourly PPP. It is found that the mean positioning accuracy in all hourly
solutions for the stations inside the EPN is improved from (3.8, 1.5, 2.8) centimeters to (0.5, 0.5, 1.4) centimeters for
the East, North and Up components, respectively. For the stations outside the EPN, some of which are over 2,000 km away from
the nearest EPN stations, the mean positioning accuracy in the East, North and Up directions still achieves (0.6, 0.6, 2.0)
centimeters, respectively, when the EPN-based UHD are applied to these stations. These results demonstrate that ambiguity
resolution at a single station can significantly improve the positioning accuracy in hourly PPP. Particularly, UHD can be
even applied to a station which is up to thousands of kilometers from the UHD-determination network, potentially showing a
great advantage over current network-based GPS augmentation systems. Therefore, it is feasible and beneficial for the operators
of GPS regional networks and providers of PPP-based online services to provide these UHD estimates as an additional product. 相似文献
12.
Application of the TaiWan Ionospheric Model to single-frequency ionospheric delay corrections for GPS positioning 总被引：2，自引：2，他引：0
The performance of a three-dimensional ionospheric electron density model derived from FormoSat3/COSMIC GPS Radio Occultation measurements, called the TaiWan Ionosphere Model (TWIM), in removing the ionospheric delays in single-frequency pseudorange observations is presented. Positioning results using TWIM have been compared with positioning results using other ionospheric models, such as the Klobuchar (KLOB) and the global ionospheric model (GIM). C/A code pseudoranges have been observed at three International GPS Service reference stations that are representative of mid-latitude (BOR1 and IRKJ) and low-latitude (TWTF) regions of the ionosphere. The observations took place during 27 geomagnetically quiet days from April 2010 to October 2011. We perform separate solutions using the TWIM, KLOB, GIM ionospheric models and carry out a solution applying no ionospheric correction at all. We compute the daily mean horizontal errors (DMEAN) and the daily RMS (DRMS) for these solutions with respect to the published reference station coordinates. It has demonstrated that TEC maps generate using the TWIM exhibit a detailed structure of the ionosphere, particularly at low-latitude region, whereas the Klobuchar and the GIM only provide the basic diurnal and geographic features of the ionosphere. Also, it is shown that even for lower satellite elevations, the TWIM provides better positioning than the Klobuchar and GIM models. Specifically, using TWIM, the difference of the uncorrected solution (no ionospheric correction), and the other solutions, relative to the uncorrected solution, is 45 % for the mean horizontal error (DMEAN) and 42 % for the horizontal root-mean-square error (DRMS). Using Klobuchar and GIM, the percent for DMEAN only reaches to about 12 % and 3 %, while the values for the DRMS are only 12 and 4 %, respectively. In the vertical direction, all models have a percentage of about 99 and 70 % for the mean vertical error (VMEAN) and vertical root-mean-square error (VRMS), respectively. These percentages show the greater impact of TWIM on the ionospheric correction compared to the other models. In at least 40 % of the observed days and across all stations, TWIM has the smallest DMEAN, VMEAN, DRMS, and VRMS daily values. These values reach 100 % at station TWTF. This shows the overall performance of TWIM is better than the Klobuchar and GIM. 相似文献
13.
The accuracy and feasibility of computing the zenith tropospheric delays (ZTDs) from data of the European Center for Medium-Range
Weather Forecasts (ECMWF) and the United States National Centers for Environmental Prediction (NCEP) are studied. The ZTDs
are calculated from ECMWF/NCEP pressure-level data by integration and from the surface data with the Saastamoinen model method
and then compared with the solutions measured from 28 global positioning system (GPS) stations of the Crustal Movement Observation
Network of China (CMONOC) for 1 year. The results are as follows: (1) the error of the integration method is 1–3 cm less than
that of the Saastamoinen model method. The agreement between the ECMWF ZTD and GPS ZTD is better than that between NCEP ZTD
and GPS ZTD; (2) the bias and root mean square difference (RMSD), especially the latter, have a seasonal variation, and the
RMSD decreases with increasing altitude while the variation with latitude is not obvious; and (3) when using the full horizontal
resolution of 0.5° × 0.5° of the ECMWF meteorological data in place of a reduced 2.5° × 2.5° grid, the mean RMSD between GPS
and ECMWF ZTD decreases by 4.5 mm. These results illuminated the accuracy and feasibility of computing the tropospheric delays
and establishing the ZTD prediction model over China for navigation and positioning with ECMWF and NCEP data. 相似文献
14.
15.
The network-based GPS technique provides a broad spectrum of corrections to support RTK (real-time kinematic) surveying and
geodetic applications. The most important among them are the ionospheric corrections generated in the reference network. The
accuracy of these corrections depends upon the ionospheric conditions and may not always be sufficient to support ambiguity
resolution (AR), and hence accurate GPS positioning. This paper presents the analyses of the network-derived ionospheric correction
accuracy under extremely varying – quiet and stormy – geomagnetic and ionospheric conditions. In addition, the influence of
the correction accuracy on the instantaneous (single-epoch) and on-the-fly (OTF) AR in long-range RTK GPS positioning is investigated,
and the results, based on post-processed GPS data, are provided. The network used here to generate the ionospheric corrections
consists of three permanent stations selected from the Ohio Continuously Operating Reference Stations (CORS) network. The
average separation between the reference stations was ∼200 km and the test baseline was 121 km long. The results show that,
during the severe ionospheric storm, the correction accuracy deteriorates to the point when the instantaneous AR is no longer
possible, and the OTF AR requires much more time to fix the integers. The analyses presented here also outline the importance
of the correct selection of the stochastic constraints in the rover solution applied to the network-derived ionospheric corrections. 相似文献
16.
17.
Application of SWACI products as ionospheric correction for single-point positioning: a comparative study 总被引：1，自引：0，他引：1
In Global Navigation Satellite Systems (GNSS) using L-band frequencies, the ionosphere causes signal delays that correspond with link related range errors of up to 100 m. In a first order approximation the range error is proportional to the total electron content (TEC) of the ionosphere. Whereas this first order range error can be corrected in dual-frequency measurements by a linear combination of carrier phase- or code-ranges of both frequencies, single-frequency users need additional information to mitigate the ionospheric error. This information can be provided by TEC maps deduced from corresponding GNSS measurements or by ionospheric models. In this paper we discuss and compare different ionospheric correction methods for single-frequency users. The focus is on the comparison of the positioning quality using dual-frequency measurements, the Klobuchar model, the NeQuick model, the IGS TEC maps, the Neustrelitz TEC Model (NTCM-GL) and the reconstructed NTCM-GL TEC maps both provided via the ionosphere data service SWACI (http://swaciweb.dlr.de) in near real-time. For that purpose, data from different locations covering several days in 2011 and 2012 are investigated, including periods of quiet and disturbed ionospheric conditions. In applying the NTCM-GL based corrections instead of the Klobuchar model, positioning accuracy improvements up to several meters have been found for the European region in dependence on the ionospheric conditions. Further in mid- and low-latitudes the NTCM-GL model provides results comparable to NeQuick during the considered time periods. Moreover, in regions with a dense GNSS ground station network the reconstructed NTCM-GL TEC maps are partly at the same level as the final IGS TEC maps. 相似文献
18.
基于北斗GEO卫星独有的静地特性,本文利用其观测数据提取电离层TEC进行磁暴期间电离层TEC时空变化研究。同时利用全球电离层格网图GIM值进行试验对比,结果表明：北斗GEO卫星提取的TEC与GIM模型值变化趋势一致,并且前者可更有效地监测电离层的细微扰动变化。在此次磁暴发生期间,亚太地区电离层TEC变化及扰动响应特征在纬度方向差异明显。其中南北半球较高纬度区域,电离层TEC在磁暴主相阶段主要表现为正响应扰动,而赤道及北半球较低纬度区域,电离层TEC在磁暴主相及恢复相阶段均产生了强度更大、持续时间更长的正响应扰动。结合现有研究,认为造成此次电离层异常扰动的激励因素主要为东向快速穿透电场的增强及热层中性成分的变化。试验结果也证明了GEO卫星可以精准有效地监测在磁暴发生时电离层TEC的变化规律及不同空间位置处TEC产生的扰动响应特征。 相似文献
19.
RINEX_HO: second- and third-order ionospheric corrections for RINEX observation files 总被引：1，自引：0，他引：1
When GNSS receivers capable of collecting dual-frequency data are available, it is possible to eliminate the first-order ionospheric
effect in the data processing through the ionosphere-free linear combination. However, the second- and third-order ionospheric
effects still remain. The first-, second- and third-order ionospheric effects are directly proportional to the total electron
content (TEC), although the second- and third-order effects are influenced, respectively, by the geomagnetic field and the
maximum electron density. In recent years, the international scientific community has given more attention to these kinds
of effects and some works have shown that for high precision GNSS positioning these effects have to be taken into consideration.
We present a software tool called RINEX_HO that was developed to correct GPS observables for second- and third-order ionosphere
effects. RINEX_HO requires as input a RINEX observation file, then computes the second- and third-order ionospheric effects,
and applies the corrections to the original GPS observables, creating a corrected RINEX file. The mathematical models implemented
to compute these effects are presented, as well as the transformations involving the earth’s magnetic field. The use of TEC
from global ionospheric maps and TEC calculated from raw pseudorange measurements or pseudoranges smoothed by phase is also
investigated. 相似文献
20.
GPS observations of the ionospheric F2-layer behavior during the 20th November 2003 geomagnetic storm over South Korea 总被引：4，自引：1，他引：3
The ionospheric F2-layer peak density (NmF2) and its height (hmF2) are of great influence on the shape of the ionospheric
electron density profile Ne (h) and may be indicative of other physical processes within the ionosphere, especially those
due to geomagnetic storms. Such parameters are often estimated using models such as the semiempirical international reference
ionosphere (IRI) models or are measured using moderately priced to expensive instrumentation, such as ionosondes or incoherent
scatter radars. Global positioning system (GPS) observations have become a powerful tool for mapping high-resolution ionospheric
structures, which can be used to study the ionospheric response to geomagnetic storms. In this paper, we describe how 3-D
ionospheric electron density profiles were produced from data of the dense permanent Korean GPS network using the tomography
reconstruction technique. These profiles are verified by independent ionosonde data. The responses of GPS-derived parameters
at the ionospheric F2-layer to the 20th November 2003 geomagnetic storm over South Korea are investigated. A fairly large
increase in the electron density at the F2-layer peak (the NmF2) (positive storm) has been observed during this storm, which
is accompanied by a significant uplift in the height of the F2 layer peak (the hmF2). This is confirmed by independent ionosonde
observations. We suggest that the F2-layer peak height uplift and NmF2 increase are mainly associated with a strong eastward
electric field, and are not associated with the increase of the O/N2 ratio obtained from the GUVI instruments aboard the TIMED satellite. It is also inferred that the increase in NmF2 is not
caused by the changes in neutral composition, but is related to other nonchemical effects, such as dynamical changes of vertical
ion motions induced by winds and E × B drifts, tides and waves in the mesosphere/lower thermosphere region, which can be dynamically
coupled upward to generate ionospheric perturbations and oscillations. 相似文献