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1.
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   

2.
Well credited and widely used ionospheric models, such as the International Reference Ionosphere or NeQuick, describe the variation of the electron density with height by means of a piecewise profile tied to the F2-peak parameters: the electron density, $N_m \mathrm{F2}$ N m F 2 , and the height, $h_m \mathrm{F2}$ h m F 2 . Accurate values of these parameters are crucial for retrieving reliable electron density estimations from those models. When direct measurements of these parameters are not available, the models compute the parameters using the so-called ITU-R database, which was established in the early 1960s. This paper presents a technique aimed at routinely updating the ITU-R database using radio occultation electron density profiles derived from GPS measurements gathered from low Earth orbit satellites. Before being used, these radio occultation profiles are validated by fitting to them an electron density model. A re-weighted Least Squares algorithm is used for down-weighting unreliable measurements (occasionally, entire profiles) and to retrieve $N_m \mathrm{F2}$ N m F 2 and $h_m \mathrm{F2}$ h m F 2 values—together with their error estimates—from the profiles. These values are used to monthly update the database, which consists of two sets of ITU-R-like coefficients that could easily be implemented in the IRI or NeQuick models. The technique was tested with radio occultation electron density profiles that are delivered to the community by the COSMIC/FORMOSAT-3 mission team. Tests were performed for solstices and equinoxes seasons in high and low-solar activity conditions. The global mean error of the resulting maps—estimated by the Least Squares technique—is between $0.5\times 10^{10}$ 0.5 × 10 10 and $3.6\times 10^{10}$ 3.6 × 10 10 elec/m $^{-3}$ ? 3 for the F2-peak electron density (which is equivalent to 7 % of the value of the estimated parameter) and from 2.0 to 5.6 km for the height ( $\sim $ ～ 2 %).  相似文献   

3.
This study carries out a quantitative analysis of the performance of ionospheric tomography in the topside ionosphere, utilizing data of October 2011 collected from 260 Global Navigation Satellite System (GNSS) stations in the Crustal Movement Observation Network of China. This tomographic reconstruction with a resolution of 2° in latitude, 2° in longitude and 20 km in altitude has more than 70 % of voxels traversed by GPS raypaths and is able to provide reliable bottom parts of ionospheric profiles. Compared with the observations measured by the Defense Meteorological Satellite Program (DMSP) satellites (F16, F17 and F18) at an altitude of 830–880 km, the results show that there is an overestimation in the reconstructed plasma density at the DMSP altitude, and the reconstruction is better during daytime than nighttime. In addition, the reconstruction at nighttime also indicates a solar activity and latitudinal dependence. In summary, with respect to DMSP measurements, the daytime bias is on average from ?0.32 × 105/cm3 to ?0.28 × 105/cm3, while the nighttime bias is between ?0.37 × 105/cm3 and ?0.24 × 105/cm3, and the standard deviation at daytime and at nighttime is, respectively, 0.082 × 105/cm3 to 0.244 × 105/cm3 and 0.086 × 105/cm3 to 0.428 × 105/cm3. This study suggests that vertical ionospheric profiles from other sources, such as ionosondes or GNSS occultation satellites, should be incorporated into ground-based GNSS topside tomographic studies.  相似文献   

4.
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   

5.
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   

6.
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   

7.
杨力  赵海山  董明  徐世依  南天浩 《测绘学报》2016,45(Z2):139-146
采用IGS发布的GIM数据,提出了一种结合滑动时窗法和临近格网点电离层TEC相关性分析法的联合分析方法,研究了震前电离层异常变化与地震的关系。通过分析震区附近5个格网点TEC的异常变化情况,发现震前电离层TEC发生明显异常变化,且格网点之间的TEC序列相关性受地震显著影响;通过分析二维电离层图的TEC异常空间分布,发现震前三天震中附近分别出现6h、12h和6h的异常。最后利用电离层层析的方法,对电离层异常时刻进行了电子密度的反演,进一步分析了电子密度在电离层异常时刻的分布情况。  相似文献   

8.
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   

9.
Paul Straus 《GPS Solutions》2005,9(2):164-173
The ionospheric occultation experiment (IOX) is a GPS occultation sensor with an ionospheric mission focus. IOX measurements of GPS L1 and L2 carrier phase during Earth limb views of setting GPS satellites are used together with the Abel transform to determine vertical profiles of electron density from which F-region peak parameters are determined. Data from a four and a half month period beginning in November 2001 are statistically binned and compared with a climatological model. To account for potential errors in interpretation that could arise from violation of the Abel transform assertion of spherical symmetry, the data are compared to both the climatology and to statistics of simulated ionospheric inversions using the climatological model. General characteristics of the climatology are reproduced by the occultation data. However, several significant discrepancies between the model and the data are observed during this near-solar maximum time period. In particular, average mid-latitude daytime densities are shown to be higher than the climatological prediction and the height of F2 layer in the post-sunset equatorial region is underestimated by up to 150 km.
Paul StrausEmail: Phone: +1-310-3365328Fax: +1-310-3361636
  相似文献   

10.
The ionospheric radiance and electron density observed by the tiny ionospheric photometer (TIP) and GPS occultation experiment (GOX) payloads on FORMOSAT-3/COSMIC satellites are applied to determine the boundaries of the auroral oval and its width in the winter nighttime ionosphere for both hemispheres. The TIP collects ionospheric emission at 135.6 nm due to electron impact excitation, while the GOX offers ionospheric electron density profiles with radio occultation (RO) technique. Comparison between them shows similar patterns of the plasma structure in the polar caps. The mean width of the auroral bands ranges between about 2 and 11° latitude in the winter nighttime and it varies with longitudes. The comparison by month suggests that the mean radius of the auroral ovals varies with the intensity of the auroral radiance.  相似文献   

11.
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   

12.
Mitigation of higher order ionospheric effects on GNSS users in Europe   总被引：2，自引：0，他引：2  
Current dual-frequency GPS measurements can only eliminate the first-order ionospheric term and may cause a higher-order range bias of several centimeters. This research investigates the second-order ionospheric effect for GNSS users in Europe. In comparison to previous studies, the electron density profiles of the ionosphere/plasmasphere are modeled as the sum of three Chapman layers describing electron densities of the ionospheric F2, F1 and E layers and a superposed exponential decay function describing the plasmasphere. The International Geomagnetic Reference Field model is used to calculate the geomagnetic field vectors at numerous points along the incoming ray paths. Based on extended simulation studies, we derive a correction formula to compute the average value of the longitudinal component of the earth’s magnetic field along the line-of-sight as a function of geographic latitude and longitude, and geometrical parameters such as elevation and azimuth angles. Using our correction formula in conjunction with the total electron content (TEC) along the line-of-sight, the second-order ionospheric term can be corrected to the millimeter level for a vertical TEC level of 1018 electrons/m2.  相似文献   

13.
Medium-scale traveling ionospheric disturbances (MSTID) are wave-like perturbations of the ionospheric plasma with wavelengths of several hundred kilometres and velocities of several hundred metres per second. MSTID is one of the most common ionospheric phenomena that generally induce the perturbations of ionospheric total electron content (TEC) by ∼1016 electron/m2, which corresponds to ∼54 ns (16.2 cm) delay at GPS L1 signal. In the past decade, several new characteristics on MSTIDs have been revealed by the TEC observations using the dense GPS receiver network in Japan. In this paper, we provide a short review of these new observations and summarize the morphological characteristics of MSTIDs in Japan.  相似文献   

14.
The crustal structure of Xiachayu-Gonghe geophysical profile in eastern Tibetan plateau is simulated with Bouguer anomaly corrected for sediments and lithosphere.The forward simulation shows that the thickness of upper crust in eastern Tibetan plateau is about 20 km,and the density is 2.78 3 3 × 10 kg/m.The bottom interface of middle crust changes from 30 km to 40 km,the density of middle crust is 2.89 3 3 × 10 kg/m.The materials with low density of 2.78 3 3 × 10 kg/mexist in middle crust,and those with hig...  相似文献   

15.
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16.
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   

17.
Analysis of inversion errors of ionospheric radio occultation   总被引：3，自引：0，他引：3  
The retrieved electron density profile of ionospheric radio occultation (RO) simulation data can be compared with the background model value during the simulation and the inversion error can be obtained exactly. This paper studies the inversion error of ionospheric RO through simulation. The sources of the inversion errors are analyzed. The impacts of measurement errors, such as the errors in phase measurements and satellite orbits, are very small and can be neglected. The approximation of straight-line propagation introduces errors at the height of the F1 layer under solar maximum condition. The spherical symmetry approximation of the electron density distribution is found to be the main source of the inversion error. The statistical results reveal some characteristics of the inversion errors. (1) The relative error increases with enhanced solar activity. (2) It is larger in winter than in equinox season, and it is smallest in summer. (3) For all seasons, it is smaller at middle latitude than at other latitudes. (4) For all seasons and geomagnetic latitudes, it is smaller at daytime than at other times. The NmF2 of the ROs from COSMIC are compared with the measurements of ionosondes, and the relative differences show the same dependencies on season, geomagnetic latitude and local time, as the relative errors of the simulated ionospheric ROs.
Xiaocheng WuEmail:
  相似文献   

18.
The majority of navigation satellites receivers operate on a single frequency and experience a positioning error due to the ionospheric delay. This can be compensated for using a variety of approaches that are compared in this paper. The study focuses on the last solar maximum. A 4D tomographic imaging technique is used to map the ionospheric electron density over the European region during 2002 and 2003. The electron density maps are then used to calculate the excess propagation delay on the L1 frequency experienced by GPS receivers at selected locations across Europe. The excess delay is applied to correct the pseudo-range single frequency observations at each location and the improvements to the resulting positioning are calculated. The real-time tomographic technique is shown to give navigation solutions that are better than empirical modelling methods and approach the accuracy of the full dual-frequency solution. The improvements in positioning accuracy vary from day to day depending on ionospheric conditions but can be up to 25 m during mid-day during these solar maximum conditions at European mid-latitudes.
Damien J. AllainEmail:
  相似文献   

19.
Ionospheric TEC predictions over a local area GPS reference network   总被引：4，自引：0，他引：4  
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   

20.
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   

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