NeQuick电离层模型在中国地区的应用

电离层延迟是影响GPS绝对定位精度的主要因素,对单频接收机尤为明显,Galileo系统广播星历拟采用NeQuick模型作为其电离层模型。本文介绍了NeQuick模型及其模型最优化,给出了利用NeQuick模型计算电离层总电子含量(TEC)的方法,利用国内部分观测台链提供的北京和武汉的TEC,并与NeQuick模型所给出的结果进行对比分析,最后给出NeQuick模型在中国地区使用的初步结论。     

Using VLBI fringe-phase information from geodetic experiments for short-period ionospheric studies

The usage of Very Long Baseline Interferometry (VLBI) fringe-phase information in geodetic VLBI is a new field of research, which can be used for the detection of short-period (i.e., several minutes) variations (scintillations) of the ionosphere. This paper presents a method for the extraction of such disturbances and discusses how dispersive influences can be separated from intra-scan delay variations. A proper functional and stochastic model for the separation of the different effects is presented and the algorithms are applied to real measurements. In an example, it is shown that a traveling ionospheric disturbance in Antarctica can be detected very precisely. A possible physical origin and the propagation properties of the disturbance are presented and the results are compared with GPS measurements. The benefit of this method for other applications is also discussed.     

Comparisons of homogeneously reprocessed GPS and VLBI long time-series of troposphere zenith delays and gradients

Troposphere parameters estimated from space-geodetic techniques, like the Global Positioning System (GPS) or Very Long Baseline Interferometry (VLBI), can be used to monitor the atmospheric water vapor content. Although the troposphere can only be monitored at discrete locations, the distribution of the instruments, at least the GPS antennas, can be assumed to be quasi-global. Critical in the data analysis are systematic effects within each single technique that significantly degrade the accuracy and especially the long-term stability of the zenith delay determination. In this paper, consistent time-series of troposphere zenith delays and gradients from homogeneously reprocessed GPS and VLBI solutions are compared for a time period of 11 years. The homogeneity of these completely reprocessed time-series is essential to avoid misinterpretations due to individual model changes. Co-located sites are used to investigate systematic effects and the long-term behavior of the two space-geodetic techniques. Both techniques show common signals in the troposphere parameters at a very high level of precision. The biases between the troposphere zenith delays are at the level of a few millimeters. On the other hand, long-term trends significantly differ for the two techniques, preventing climatological interpretations at present. Tests assume these differences to be due to mathematical artifacts such as different sampling rates and unmodeled semi-annual signals with varying amplitudes.     

Monitoring Seasonal Variations of Ionospheric TEC Using GPS Measurements

The regional ionospheric model is adopted to determine satellite-plus-receiver differential delay. The satellite-plus-receiver differential delay is estimated as constant values for each day. Dual-frequency GPS pseudo-ranges observables are used to compute vertical TEC (VTEC). All the monthly mean VTEC profiles are represented by graphs using GPS data of the Beijing IGS site between 2000 and 2004. The monthly averaged values and amplitudes of VTEC are also represented by graphs. The results indicate that the VTEC has seasonal dependency. The monthly averaged values and amplitudes of VTEC in 2000 are about 2 times larger than that in 2004. The maximum VTEC values are observed in March and April, while the minimum VTEC values are observed in December. The seasonal variations trend is found to be similar after polynomial fitting between 2000 and 2004.     

两种GPS测定电离层电子密度模型的探讨

详细推导出利用GPS双频码距及载波相位观测值进行电离层子密度求定的Klobuchar模型以及Georgiadou模型,给出了求定这两种模型参数的数学表达,从理论上指出该两种模型适合单历元解算的基本条件,通过实例进行了两种模型的电离层修正误差与误差频率的分析和比较。结果表明,与Klobuchar模型相比,Georgiadou模型具有表达形式简单,对模型参数的初值精度要求较低,数据利用率较高,参数估计精度较高等优点。     

Ionospheric Alfvén Resonator Control over the Frequency-Variable Pc1 Event in Finland on May 14, 1997

The ionospheric Alfvén resonator (IAR) control mechanism over the EMIC wave transmission to the ground is demonstrated on a selected long-term frequency-variable subauroral Pcl event. The proper ionospheric plasma data obtained from EISCAT were accessible in a wide altitude range. Applying the numerical method of simulation of a realistic inhomogeneous IAR, the problem of appearance and disappearance of the ground Pc1 signal record was clarified on the basis of coincidence between the EMIC wave frequency spectrum and the IAR fundamental frequency peak (the frequency window). A shift of the signal source field line to lower latitudes during the development of the disturbance was noticed, and the signal frequency variation on the ground was modelled in the nonstationary IAR. Variation of the IAR altitude structure in the fundamental frequency was illustrated on altitude profiles of the normalized wave magnetic field amplitude in the horizontal and vertical components. Particular conditions of L - and R -wave mode incidence were assumed. The electron density vertical profile of IAR determines the effective resonator dimensions. In this way the IAR fundamental frequency window controls the signal within the ionosphere and on the ground.     

GNSS空间信号质量评估系统接收通道性能测试

GNSS空间信号质量评估系统的接收通道是评估导航信号质量的主要误差源之一。通过分析接收通道特性引起的信号幅度误差、相位失真、频率偏移等现象,研究了接收通道增益平坦度、幅度误差、相位误差、频率偏移、矢量误差幅度、群时延等机理,提出了相应的测试方法,测试结果表明接收通道性能能够满足空间信号质量评估的要求。     

BDS中长基线三频RTK算法研究

针对BDS中长基线RTK定位中整周模糊度受大气延迟误差影响难以正确固定的问题,提出一种BDS中长基线三频整周模糊度确定方法。采用MW组合确定B2-B3超宽巷整周模糊度,利用B2-B3超宽巷和B1-B3宽巷组合观测值所受电离层延迟误差较接近的特点,确定B1-B3宽巷整周模糊度。利用无电离层组合解算窄巷整周模糊度和相对天顶对流层延迟误差,最终实现实时动态定位。利用实测的BDS中长基线进行算法验证,结果表明,该方法可有效固定中长基线三频载波相位整周模糊度,获得cm级定位精度。     

GPS-based regional ionospheric models and their suitability in Antarctica

There are a number of ionospheric models available for research and application, such as the polynomial model, generalized trigonometric series function model, low degree spherical harmonic function model, adjusted spherical harmonic function model, and spherical cap harmonic function analysis. Using observations from more than 40 continuously operating stations across Antarctica in 2010, ifve models are compared with regard to their precision and applicability to polar regions. The results show that all the models perform well in Antarctica with 0.1 TECU of residual mean value and 2 TECU of root mean square error.     

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