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1.
High-frequency variability of the ionosphere, or irregularities, constitutes the main threat for real-time precise positioning techniques based on Global Navigation Satellite Systems (GNSS) measurements. Indeed, during periods of enhanced ionospheric variability, GNSS users in the field—who cannot verify the integrity of their measurements—will experience positioning errors that can reach several decimeters, while the nominal accuracy of the technique is cm-level. In the frame of this paper, a climatological analysis of irregularities over the European mid-latitude region is presented. Based on a 10 years GPS dataset over Belgium, the work analyzes the occurrence rate (as a function of the solar cycle, season and local time) as well as the amplitude of ionospheric irregularities observed at a single GPS station. The study covers irregularities either due to space weather events (solar origin) or of terrestrial origin. If space weather irregularities are responsible for the largest effects in terms of ionospheric error, their occurrence rate highly depends on solar activity. Indeed, the occurrence rate of ionospheric irregularities is about 9 % during solar maximum, whereas it drops to about 0 % during medium or low solar activity periods. Medium-scale ionospheric disturbances (MSTIDs) occurring during daytime in autumn/winter are the most recurrent pattern of the time series, with yearly proportions slightly varying with the solar cycle and an amplitude of about 10 % of the TEC background. Another recurrent irregularity type, though less frequent than MSTIDs, is the noise-like variability in TEC observed during summer nighttime, under quiet geomagnetic conditions. These summer nighttime irregularities exhibit amplitudes ranging between 8 and 15 % of the TEC background. 相似文献
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利用中国南部地区七个站点的2004年GPS观测数据,对赤道异常中国扇区电离层TEC的北驼峰位置和时间以及驼峰北侧电离层梯度进行了分析,结果表明:驼峰位置随季节改变,介于地理北纬17.5°~22.5°之间,冬季月份相对为低,分季月份相对为高,年平均位置约在北纬20°附近;驼峰出现时间也随季节在地方时13~16 h之间变化,冬季月份相对为早,夏季月份相对为晚,其出现时间的年平均值前者在地方时14 h前后,后者约在地方时15~16 h之间。驼峰区电离层TEC存在纬向梯度,其梯度也随地方时和季节而改变,夜侧梯度在地方时4.5 h前后为极小,且在不同季节其变化幅度不大,而日侧梯度在地方时13.5~16.5 h时段出现极大,且在不同季节差异较大,分季要高于冬季和夏季。 相似文献
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The ionospheric eclipse factor method (IEFM) and its application to determining the ionospheric delay for GPS 总被引:4,自引:1,他引:3
A new method for modeling the ionospheric delay using global positioning system (GPS) data is proposed, called the ionospheric
eclipse factor method (IEFM). It is based on establishing a concept referred to as the ionospheric eclipse factor (IEF) λ
of the ionospheric pierce point (IPP) and the IEF’s influence factor (IFF) . The IEF can be used to make a relatively precise distinction between ionospheric daytime and nighttime, whereas the IFF
is advantageous for describing the IEF’s variations with day, month, season and year, associated with seasonal variations
of total electron content (TEC) of the ionosphere. By combining λ and with the local time t of IPP, the IEFM has the ability to precisely distinguish between ionospheric daytime and nighttime, as well as efficiently
combine them during different seasons or months over a year at the IPP. The IEFM-based ionospheric delay estimates are validated
by combining an absolute positioning mode with several ionospheric delay correction models or algorithms, using GPS data at
an international Global Navigation Satellite System (GNSS) service (IGS) station (WTZR). Our results indicate that the IEFM
may further improve ionospheric delay modeling using GPS data. 相似文献
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利用2008-2015年(第24太阳活动周)中国地壳运动监测网络(CMONOC)武汉站(30.5°N,114.4°E)GPS双频接收机监测的垂直总电子含量(VTEC)数据,分析电离层VTEC变化特性,并讨论VTEC与太阳活动的相关性.结果表明,VTEC估值周日变化在14:00-16:00LT左右达到最大值;同时,电离层VTEC也表现出明显的逐日变化特性,特别是在VTEC峰值处呈现较大差异.在太阳活动高年(2011-2015),VTEC变化呈现明显的双峰结构,即所谓的"半年异常"现象,春季峰值大于秋季峰值,"冬季异常"也更为明显.在各个季节(除春季外),VTEC与F10.7p的相关性最好,与F10.7的相关性次之,与太阳黑子数(SSN)的相关性稍弱;秋季VTEC与太阳活动的相关性最好(MaxF10.7p=0.92232,MaxSSN=0.85575),冬季VTEC与太阳活动的相关性最差(MinF10.7p=0.79028,MinSSN=0.72703). 相似文献
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Temporal and spatial variability of the bias between TOPEX- and GPS-derived total electron content 总被引:2,自引:1,他引:2
Total electron content (TEC) predictions made with the GPS-based la plata ionospheric model (LPIM) and the International Reference Ionosphere (IRI95) model were compared to estimates from the dual-frequency altimeter onboard the TOPEX/Poseidon (T/P) satellite. LPIM and IRI95 were evaluated for the location and time of available T/P data, from January 1997 to December 1998. To investigate temporal and spatial variations of the TEC bias between T/P and each model, the region covered by T/P observations was divided into ten latitude bands. For both models and for all latitudes, the bias was mainly positive (i.e. T/P values were larger); the LPIM bias was lower and less variable than the IRI95 bias. To perform a detailed analysis of temporal and spatial variability of the T/P-LPIM TEC bias, the Earth’s surface was divided into spherical triangles with 9°-sides, and a temporally varying regression model was fitted to every triangle. The highest TEC bias was found over the equatorial anomalies, which is attributed to errors in LPIM. A significant TEC bias was found at 40°N latitude, which is attributed to errors in the T/P Sea State Bias (SSB) correction. To separate systematic errors in the T/P TEC from those caused by LPIM, altimeter range biases estimated by other authors were analysed in connection with the TEC bias. This suggested that LPIM underestimates the TEC, particularly during the Southern Hemisphere summer, while T/P C-band SSB calibration is worse during the Southern Hemisphere winter. 相似文献
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中纬度夏季夜间异常(midlatitude summer nighttime anomaly, MSNA)区域内的总电子含量(total electron content, TEC)的日变特性存在季节性差异,能否有效描述MSNA的特征是检验电离层TEC经验模型精度的关键指标之一.针对MSNA现象,提出了一种适合MSNA... 相似文献
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适用于不同尺度区域的Klobuchar-like电离层模型 总被引:1,自引:0,他引:1
导航定位中运用最广泛的电离层修正模型是Klobuchar模型,但经典的Klobuchar模型不能满足日益增长的导航定位精度的需求,因此不同的精化模型被提出。本文利用GIMs分析了夜间电离层随地方时的变化和电离层电子总含量随纬度的变化情况,在对各种适用范围较广的模型精化方案进行归纳总结的基础上,提出了一种适用于不同尺度区域的Klobuchar-like模型,并利用不同太阳活动时期不同季节的GIMs建立了适用于单站、大区域和全球的Klobuchar-like模型、14参数Klobuchar模型和8参数Klobuchar模型。Klobuchar-like模型单站、区域、全球的修正率分别达到了92.96%、91.55%、72.67%,均高于14参数、8参数Klobuchar模型和GPS Klobuchar模型,表明了该模型的有效性与实用性。 相似文献
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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
10.
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
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电离层延迟误差是卫星导航和定位中不可忽略的重要误差,全球电离层总电子含量(TEC)格网数据因其将全球按规则的经纬度格网化,并给出了相应格网点的电离层TEC值,从而为用户使用提供了极大的便利.本文基于Linux Shell脚本编写简单、快速和容易维护等优点,利用Shell脚本对电离层TEC格网数据进行提取和分析处理,主要包括全球和自定义区域电离层TEC数据提取、均值计算、格网经纬度互差计算、最值提取等应用,可为基于全球电离层格网(GIM)数据对全球或区域电离层TEC周年变化、季节变化、周日变化规律以及时空变化特性等相关规律的分析研究提供一定的参考. 相似文献
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威德尔海异常是西南极沿海地区在夏季出现的电离层异常现象。本文用西南极地区的GPS跟踪站数据和测高卫星Jason-2数据,分别提取了陆地和海洋地区大范围的电离层TEC参数。GPS反演结果的优势是获取测站上空高精度的TEC时间序列,测高反演的结果整体与GPS的结果精度相当,虽然测高的时间分辨率较低,但其优势是获取海洋广大区域的TEC值。两种观测手段的研究区域互补,可以充分观测威德尔海异常在西南极的变化特征,从空间上来看,威德尔海异常出现在以别林斯高晋海为中心的广大区域,而威德尔海异常也是覆盖了西南极的别林斯高晋海、威德尔海以及可达80°S的西南极陆地区域。从时间上来看,出现时段在每年的10月底到次年3月初,夜晚电子密度增加,白天电子密度降低,随着太阳活动的增强,其异常程度也变大。 相似文献
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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
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利用GPS双频观测数据分析了仪器偏差对计算电离层TEC的影响,结果表明忽略仪器偏差的影响不能正确反映测站上空电离层总电子含量的变化规律。验证了短期内仪器偏差的稳定性,并在此基础上研究了2005年太阳活动低峰年区域电离层VTEC的周年变化规律,揭示了电离层VTEC半年变化、季节性变化及冬季异常等现象。 相似文献
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A new global TEC model for estimating transionospheric radio wave propagation errors 总被引:4,自引:0,他引:4
Space-based navigation and radar systems operating at single frequencies of <10 GHz require ionospheric corrections of the
signal delay or range error. Because this ionospheric propagation error is proportional to the total electron content of the
ionosphere along the ray path, a user friendly TEC model covering global scale and all levels of solar activity should be
helpful in various applications. Since such a model is not available yet, we present an empirical model approach that allows
determining global TEC very easily. Although the number of model coefficients and parameters is rather small, the model describes
main ionospheric features with good quality. Presented is the empirical approach describing dependencies on local time, geographic/geomagnetic
location and solar irradiance and activity. The non-linear approach needs only 12 coefficients and a few empirically fixed
parameters for describing the broad spectrum of TEC variation at all levels of solar activity. The model approach is applied
on high-quality global TEC data derived by the Center for Orbit Determination in Europe (CODE) at the University of Berne
over more than half a solar cycle (1998–2007). The model fits to these input data with a negative bias of 0.3 TECU and a RMS
deviation of 7.5 TECU. As other empirical models too, the proposed Global Neustrelitz TEC
Model NTCM-GLis climatological, i.e. the model describes the average behaviour under quiet geomagnetic conditions. During severe space
weather events the actual TEC data may deviate from the model values considerably by more than 100%. A preliminary comparison
with independent data sets as TOPEX/Poseidon altimeter data reveals similar results for NeQuick and NTCM-GL with RMS deviations
in the order of 5 and 11 TECU (1 TECU = 1016 electrons/m2) for low and high-solar activity conditions, respectively. The more extended data base of ionosphere information that accumulates
in the coming years will help in further improving the set of coefficients of the model. 相似文献
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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
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为了分析单站区域电离层总电子含量(total electron content,TEC)模型的适用范围和精度,基于2~15阶次球谐函数,分别建立了欧洲区域16个单站区域电离层TEC模型,生成了区域格网TEC,并与欧洲定轨中心(Center for Orbit Determination in Europe,CODE)、... 相似文献
20.
Ionospheric delay is a dominant error source in Global Navigation Satellite System (GNSS). Single-frequency GNSS applications require ionospheric correction of signal delay caused by the charged particles in the earth’s ionosphere. The Chinese Beidou system is developing its own ionospheric model for single-frequency users. The number of single-frequency GNSS users and applications is expected to grow fast in the next years in China. Thus, developing an appropriate ionospheric model is crucially important for the Chinese Beidou system and worldwide single-frequency Beidou users. We study the performance of five globally accessible ionospheric models Global Ionospheric Map (GIM), International Reference Ionosphere (IRI), Parameterized Ionospheric Model (PIM), Klobuchar and NeQuick in low- and mid-latitude regions of China under mid-solar activity condition. Generally, all ionospheric models can reproduce the trend of diurnal ionosphere variations. It is found that all the models have better performances in mid-latitude than in low-latitude regions. When all the models are compared to the observed total electron content (TEC) data derived from GIM model, the IRI model (2012 version) has the best agreement with GIM model and the NeQuick has the poorest agreement. The RMS errors of the IRI model using the GIM TEC as reference truth are about 3.0–10.0 TECU in low-latitude regions and 3.0–8.0 TECU in mid-latitude regions, as observed during a period of 1 year with medium level of solar activity. When all the ionospheric models are ingested into single-frequency precise point positioning (PPP) to correct the ionospheric delays in GPS observations, the PIM model performs the best in both low and mid-latitudes in China. In mid-latitude, the daily single-frequency PPP accuracy using PIM model is ~10 cm in horizontal and ~20 cm in up direction. At low-latitude regions, the PPP error using PIM model is 10–20 cm in north, 30–40 cm in east and ~60 cm in up component. The single-frequency PPP solutions indicate that NeQuick model has the lowest accuracy among all the models in both low- and mid-latitude regions of China. This study suggests that the PIM model may be considered for single-frequency GNSS users in China to achieve a good positioning accuracy in both low- and mid-latitude regions. 相似文献