共查询到20条相似文献，搜索用时 46 毫秒
1.
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
2.
Electron density profiles in the equatorial ionosphere observed by the FORMOSAT-3/COSMIC and a digisonde at Jicamarca 总被引：1，自引：0，他引：1
Jann-Yenq Liu Chien-Chih Lee Jhih-Yung Yang Chao-Yen Chen Bodo W. Reinisch 《GPS Solutions》2010,14(1):75-81
We examine for the first time the ionospheric electron density profiles concurrently observed by the GPS occultation experiment
(GOX) onboard the FORMOSAT-3/COSMIC (F3/C) and the ground-based digisonde portable sounder DPS-4 at Jicamarca (12°S, 283°W,
1°N geomagnetic) in 2007. Our results show that the F3/C generally underestimates the F2-peak electron density NmF2 and the
F2-peak height hmF2. On the other hand, when the equatorial ionization anomaly (EIA) pronouncedly appears during daytime,
the total electron content (TEC) derived from the radio occultation of the GPS signal recorded by the F3/C GOX is significantly
enhanced. This results in the NmF2 at Jicamarca being overestimated by the Abel inversion on the enhanced TEC during the afternoon
period. 相似文献
3.
掩星观测能够提供地面到低轨卫星轨道高度处的整个电离层电子密度剖面,对于顶部电离层的研究有重要的作用。本文利用COSMIC(constellation observing system for meteorology ionosphere and climate)掩星数据反演了电子密度剖面,提取了F2层峰值高度(hmF2)、F2层峰值密度(NmF2)、垂直标尺高(vertical scale height,VSH)等电离层参数,研究了南极地区的F2层在太阳活动周期内的变化、年际变化、周日变化等,并且重点分析了南极地区的顶部电离层的垂直结构特征,尤其是威德尔海异常在垂直方向上的变化。结果表明,整个南极的hmF2每日均值在250~300 km左右,NmF2每日均值在1~8×1011 el/m3之间,VSH每日均值在100~250 km,威德尔海异常主要表现在顶部电子密度的增强和底部电子密度的减少。 相似文献
4.
GPS tomography in the polar cap: comparison with ionosondes and in situ spacecraft data 总被引：2，自引：1，他引：1
Dimitry Pokhotelov P. T. Jayachandran Cathryn N. Mitchell John W. MacDougall Michael H. Denton 《GPS Solutions》2011,15(1):79-87
Tomographic 4D reconstructions of ionospheric anomalies appearing in the high-latitude polar cap region are compared with
plasma density measurements by digital ionosonde located near the north magnetic pole at Eureka station and with in situ plasma
measurements on-board DMSP spacecraft. The moderate magnetic storm of 14–17 October 2002 is taken as an example of a geomagnetic
disturbance which generates large-scale ionospheric plasma anomalies at mid-latitudes and in the polar cap region. Comparison
of the GPS tomographic reconstructions over Eureka station with the ionosonde measurements of the F layer peak densities indicates
that the GPS tomography correctly predicts the time of arrival and passage of the ionospheric tongue of ionization over the
magnetic pole area, although the tomographic technique appears to under-estimate the value of F peak plasma density. Comparison
with the in situ plasma measurements by the DMSP SSIES instruments shows that the GPS tomography correctly reproduces the
large-scale spatial structure of ionospheric anomalies over a wide range of latitudes from mid-latitudes to the high-latitude
polar cap region, though the tomographic reconstructions tend to over-estimate the density of the topside ionosphere at 840 km
DMSP orbit. This study is essential for understanding the quality and limitations of the tomographic reconstruction techniques,
particularly in high-latitude regions where GPS TEC measurements and other ionospheric data sources are limited. 相似文献
5.
6.
将在一定时空限定范围内的不同低轨卫星COSMIC、GRACE、CHAMP、FY3C的电离层掩星电子密度剖面定义为一个掩星对来对比分析不同类型掩星电离层产品。结果表明：COSMIC掩星对之间的电子密度剖面整体轮廓符合得很好，电子密度剖面主要在250 km以下和500 km以上存在较大的偏差，250~500 km的电子密度整体偏差较小，统计得到的COSMIC掩星对的电子密度参量NmF2和hmF2的相关系数能分别达到0.99和0.97，具有高度相关性，不同COSMIC卫星之间没有明显的系统误差；COSMIC、GRACE、CHAMP和FY3C不同低轨卫星间的电子密度剖面略有差异，通过统计电子密度参量NmF2和hmF2之间的相关系数，COSMIC和CHAMP的相关系数分别为0.95和0.86，COSMIC和GRACE的相关系数分别为0.98和0.94，COSMIC和FY3C的相关系数分别为0.96和0.92，不同掩星类型之间的电子密度参量之间也具有高度相关性，验证了不同卫星任务GPS掩星电离层剖面的一致性。 相似文献
7.
Chun-Chieh Hsiao J. Y. Liu K.-I. Oyama N. L. Yen Y. A. Liou S. S. Chen J. J. Miau 《GPS Solutions》2010,14(1):83-89
The seismo-ionospheric precursor prior to the Mw7.9 earthquake near Wenchuan, China, on 12 May 2008 was observed by the FORMOSAT-3/COSMIC
satellite constellation. By binning radio occultation observations, the three-dimensional ionospheric structure can be obtained
to monitor the ionospheric electron density variation prior to the earthquake. It has been determined that near the epicenter
the F2-peak height, hmF2, descends about 25 km and the F2-peak electron density, NmF2, decreases about 2 × 105 el/cm3 around noon within 5 days prior to the earthquake. The integrated electron content decreases more than 2 TECU between 250
and 300 km altitude. 相似文献
8.
Ionospheric electron density observed by FORMOSAT-3/COSMIC over the European region and validated by ionosonde data 总被引：4，自引：0，他引：4
Andrzej Krankowski Irina Zakharenkova Anna Krypiak-Gregorczyk Irk I. Shagimuratov Pawel Wielgosz 《Journal of Geodesy》2011,85(12):949-964
This research is motivated by the recent IGS Ionosphere Working Group recommendation issued at the IGS 2010 Workshop held
in Newcastle, UK. This recommendation encourages studies on the evaluation of the application of COSMIC radio occultation
profiles for additional IGS global ionosphere map (GIM) validation. This is because the reliability of GIMs is crucial to
many geodetic applications. On the other hand, radio occultation using GPS signals has been proven to be a promising technique
to retrieve accurate profiles of the ionospheric electron density with high vertical resolution on a global scale. However,
systematic validation work is still needed before using this powerful technique for sounding the ionosphere on a routine basis.
In this paper, we analyze the properties of the ionospheric electron density profiling retrieved from COSMIC radio occultation
measurements. A comparison of radio occultation data with ground-based measurements indicates that COSMIC profiles are usually
in good agreement with ionosonde profiles, both in the F2 layer peak electron density and the bottom side of the profiles.
For this comparison, ionograms recorded by European ionospheric stations (DIAS network) in 2008 were used. 相似文献
9.
Dennis Odijk 《GPS Solutions》2001,5(2):29-42
Due to the maximum of the solar cycle, ionospheric activity increased considerably last year. At frequent times warning were
sent out announcing geomagnetic storms disturbing the ionospheric electron content. In this article the influence of such
geomagnetic storms on fast and precise GPS positioning (for surveying applications at midlatitude regions) is studied. And
here with “fast” it is aimed at the shortest observation time possible: carrier ambiguity resolution and position estimation
using only one single epoch of data. To apply this instantaneous data processing technique successfully to GPS baselines of
medium length (up to 50 km), additional ionospheric information is inevitable, not only under geomagnetic storm but also under
more quiet conditions. However, in this article it will be shown that under geomagnetic storm conditions, even for rather
short baselines (<10 km), for which the ionospheric delays under more quiet conditions could be neglected, one has to account
for significant relative ionospheric delays. Therefore an important facet of this contribution is the investigation of how
to process baselines of varying length in a more uniform way, making use of a permanent GPS network (if available in the surveying
area) and a stochastic modeling technique of the ionospheric delays. ? 2001 John Wiley & Sons, Inc. 相似文献
10.
In 1994, Hajj et al. (1994) proposed the use of radio occultation data in ionospheric imaging. The advantages gained by including this data source are examined in this paper. Many data sources including ground-based and satellite-based observations are available for the events of the April 2002 ionospheric disturbance. This period has been chosen to study simultaneous images of the disturbed ionosphere over the USA and Europe. A 4D tomographic imaging technique known as Multi-instrument Data Analysis System (MIDAS) (Mitchell and Spencer, 2003) is applied in this study. The primary purpose of the study is to compare images produced with and without the use of radio-occultation data. The work investigates whether GPS occultation combined with ground-based GPS data improves the determination of peak height and peak density in the images. The results indicate that the occultation data improve both the peak height and the peak density in the images. The use of ionosonde data is also examined and the results are compared between the USA and Europe. 相似文献
11.
Dudy D. Wijaya Haris Haralambous Christina Oikonomou Wedyanto Kuntjoro 《Journal of Geodesy》2017,91(9):1117-1133
The critical frequency of ionospheric F2 layer (foF2) is a measure of the highest frequency of radio signal that may be reflected back by the F2 layer, and it is associated with ionospheric peak electron density in the F2 layer. Accurate long-term foF2 variations are usually derived from ionosonde observations. In this paper, we propose a new method to observe foF2 using a stand-alone global positioning system (GPS) receiver. The proposed method relies on the mathematical equation that relates foF2 to GPS observations. The equation is then implemented in the Kalman filter algorithm to estimate foF2 at every epoch of the observation (30-s rate). Unlike existing methods, the proposed method does not require any additional information from ionosonde observations and does not require any network of GPS receivers. It only requires as inputs the ionospheric scale height and the modeled plasmaspheric electron content, which practically can be derived from any existing ionospheric/plasmaspheric model. We applied the proposed method to estimate long-term variations of foF2 at three GPS stations located at the northern hemisphere (NICO, Cyprus), the southern hemisphere (STR1, Australia) and the south pole (SYOG, Antarctic). To assess the performance of the proposed method, we then compared the results against those derived by ionosonde observations and the International Reference Ionosphere (IRI) 2012 model. We found that, during the period of high solar activity (2011–2012), the values of absolute mean bias between foF2 derived by the proposed method and ionosonde observations are in the range of 0.2–0.5 MHz, while those during the period of low solar activity (2009–2010) are in the range of 0.05–0.15 MHz. Furthermore, the root-mean-square-error (RMSE) values during high and low solar activities are in the range of 0.8–0.9 MHz and of 0.6–0.7 MHz, respectively. We also noticed that the values of absolute mean bias and RMSE between foF2 derived by the proposed method and the IRI-2012 model are slightly larger than those between the proposed method and ionosonde observations. These results demonstrate that the proposed method can estimate foF2 with a comparable accuracy. Since the proposed method can estimate foF2 at every epoch of the observation, it therefore has promising applications for investigating various scales (from small to large) of foF2 irregularities. 相似文献
12.
Local variability in total electron content can seriously affect the accuracy of GNSS real-time applications. We have developed
software to compute the positioning error due to the ionosphere for all baselines of the Belgian GPS network, called the Active
Geodetic Network (AGN). In a first step, a reference day has been chosen to validate the methodology by comparing results
with the nominal accuracy of relative positioning at centimeter level. Then, the effects of two types of ionospheric disturbances
on the positioning error have been analyzed: (1) Traveling ionospheric disturbances (TIDs) and (2) noise-like variability
due to geomagnetic storms. The influence of baseline length on positioning error has been analyzed for these three cases.
The analysis shows that geomagnetic storms induce the largest positioning error (more than 2 m for a 20 km baseline) and that
the positioning error depends on the baseline orientation. Baselines oriented parallel to the propagation direction of the
ionospheric disturbances are more affected than others. The positioning error due to ionospheric small-scale structures can
be so identified by our method, which is not always the case with the modern ionosphere mitigation techniques. In the future,
this ionospheric impact formulation could be considered in the development of an integrity monitoring service for GNSS relative
positioning users. 相似文献
13.
Patricia Doherty joins the regular contributors of this column to discuss the correlation between measurements of solar 10.7
cm radio flux and ionospheric range delay effects on GPS. Mrs. Doherty has extensive experience in the analysis of ionospheric
range delays from worldwide systems and in the utilization and development of analytical and theoretical models of the Earth's
ionosphere.
Ionospheric range delay effects on GPS and other satellite ranging systems are directly proportional to the Total Electron
Content (TEC) encountered along slant paths from a satellite to a ground location. TEC is a highly variable and complex parameer
that is a function of geographic location, local time, season, geomagnetic activity, and solar activity. When insufficiently
accounted for, ionospheric TEC can seriously limit the performance of satellite ranging applications. Since the ionosphere
is a dispersive medium, dual-frequency Global Positoning System (GPS) users can make automatic corrections for ionospheric
range delay by computing the apparent difference in the time delays between the two signals. Single-frequency GPS users must
depend on alternate methods to account for the ionospheric range delay. Various models of the ionosphere have been used to
provide estimates of ionospheric range delay. These models range from the GPS system's simple eight-coefficient algorithm
designed to correct for approximately 50% rms of the TEC, to state-of-the-art models derived from physical first principles,
which can correct for up to 70 to 80% rms of the TEC but at a much greater computational cost.
In an effort to improve corrections for the day-to-day variability of the ionosphere, some attempts have been made to predict
the TEC by using the daily values of solar 10.7 cm radio flux (F10,7). The purpose of this article is to show that this type of prediction is not useful due to irregular, and sometimes very
poor, correlation between daily values of TEC and F10.7. Long-term measurements of solar radio flux, however, have been shown to be well correlated with monthly mean TEC, as well
as with the critical frequency of the inonospheric F2 region (foF2), which is proportional to the electron density at the
peak of the ionospheric F2 region. ? 2000 John Wiley & Sons, Inc. 相似文献
14.
15.
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
16.
Impact of the Halloween 2003 ionospheric storm on kinematic GPS positioning in Europe 总被引：2，自引：0，他引：2
N. Bergeot C. Bruyninx P. Defraigne S. Pireaux J. Legrand E. Pottiaux Q. Baire 《GPS Solutions》2011,15(2):171-180
Using dual-frequency data from 36 GPS stations from the EUREF Permanent Network (EPN), the influence of the October 30, 2003
Halloween geomagnetic storm on kinematic GPS positioning is investigated. The Halloween storm induced ionospheric disturbances
above the northern part of Europe and Scandinavia. It is shown that kinematic position repeatabilities for this period are
mainly affected for stations in northern Europe with outliers reaching 12 cm in the horizontal, and 26 cm in the vertical.
These magnitudes are shown to be possibly due to the second-order ionospheric delays on GPS signals, not accounted for in
the kinematic GPS positioning analysis performed. In parallel, we generate hourly TEC (Total Electron Content) maps on a 1° × 1°
grid using the dense EPN network. These TEC maps do not use any interpolation but provide a high resolution in the time and
space and therefore allow to better evidence small structures in the ionosphere than the classical 2-hourly 2.5° × 5° grid
Global Ionospheric TEC Maps (GIM). Using the hourly 1° × 1° TEC maps, we reconstruct and refine exactly the zones of intense
ionosphere activity during the storm, and we show the correlation between the ionospheric activity and assess the quality
of GPS-based kinematic positioning performed in the European region. 相似文献
17.
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
18.
Differential ionospheric slant delays are obtained from a quiet-time, three-dimensional ionospheric electron density model, called the TaiWan Ionosphere Model (TWIM), to be used in code-based differential GPS positioning. The code observations are acquired from nine continuously operating GPS stations around Taiwan whose baseline ranged from 19 to 340 km. Daily 24-hour epoch-per-epoch positioning obtained for 70 most geomagnetic quiet days (2008–2010) for each of the 72 baselines. The performance of TWIM has been compared with the standard operational Klobuchar model (KLB) used by typical single-frequency receivers and the IGS global ionospheric model (GIM). Generally, TWIM performed well in reducing the differential ionospheric delay especially for long baselines and different levels of low solar activity. It has a much better performance compared to the operational KLB model. TWIM also performed similarly with GIM, though GIM has the best performance overall. GIM has the best ionospheric gradient estimates among the three models whose differential ionospheric delay-to-horizontal error ratio is more than 0.25. This is followed closely by TWIM with about 0.20. KLB only has a ratio of <0.10. The similarity of the performance of TWIM and GIM demonstrates the feasibility of TWIM in correcting for differential ionospheric delays in the C/A code pseudorange that is caused by electron density gradients in the ionosphere. It can provide decimeter-to-centimeter level accuracy in differential GPS positioning for single-frequency receivers during geomagnetic quiet conditions across all seasons and different levels of low solar activities. 相似文献
19.
S. Pireaux P. Defraigne L. Wauters N. Bergeot Q. Baire C. Bruyninx 《GPS Solutions》2010,14(3):267-277
In high-precision geodetic time and frequency transfer, which requires precise modeling of code and carrier phase GPS data,
the ionosphere-free combinations P
3
and L
3
of the codes and carrier phases, made on the two GPS frequencies, are used to remove the first-order ionospheric effect.
We quantify the impact of the residual second- and third-order ionospheric effects on geodetic time and frequency transfer
solutions for continental and intercontinental baselines. All time transfer computations are done using the ATOMIUM software,
developed at the Royal Observatory of Belgium. In order to avoid contamination by some imperfect modeling of the second- and
third-order ionospheric effects in the satellite clock products, only single-difference, common-view processing is used, based
on code and carrier phase measurements. The results are shown for weak and strong solar activity, as well as for particular
epochs of ionospheric storms. Second-order ionospheric delays can lead to corrections up to about 10 ps in the common-view
clock solution of intercontinental baselines with very different longitudes. However, realistic values of the geomagnetic
field in the ionosphere are required to assess the amplitude of second-order ionospheric effects in time and frequency transfer
during an ionospheric storm. 相似文献
20.
Jian Kong Yibin Yao Chen Zhou Yi Liu Changzhi Zhai Zemin Wang Lei Liu 《Journal of Geodesy》2018,92(11):1255-1266
The Co-Seismic Ionospheric Disturbance of the 2015 Nepal earthquake is analyzed in this paper. GNSS data are used to obtain the Satellite-Station TEC sequences. After removing the de-trended TEC variation, a clear ionospheric disturbance was observed 10 min after the earthquake, while the geomagnetic conditions, solar activity, and weather condition remained calm according to the Kp, Dst, F10.7 indices and meteorological records during the period of interest. Computerized ionosphere tomography (CIT) is then used to present the tridimensional ionosphere variation with a 10-min time resolution. The CIT results indicate that (1) the disturbance of the ionospheric electron density above the epicenter during the 2015 Nepal earthquake is confined at a relatively low altitude (approximately 150–300 km); (2) the ionospheric disturbances on the west side and east sides of the epicenter are precisely opposite. A newly established electric field penetration model of the lithosphere–atmosphere–ionosphere coupling is used to investigate the potential physical mechanism. 相似文献