基于BDS/GPS和经验模型的区域电离层建模

基于北斗卫星导航系统（BDS）和全球定位系统（GPS）实测电离层穿刺点（IPP）数据，结合国际参考电离层（IRI）经验模型历史数据，提出一种对区域二维电离层总电子含量（TEC）进行高精度建模的方法.针对缺乏穿刺点的区域内短时间电离层建模时精度较低且各时段穿刺点空间分布不同的问题，该方法使用IRI模型在建模区域内均匀添加虚拟穿刺点数据，并根据与实测穿刺点的距离，使用构造的权重计算公式赋予其动态权重值，通过加权最小二乘法进行球谐模型参数解算.与欧洲定轨中心（CODE）发布的全球电离层图（GIM）进行数据比对发现，相对于只使用BDS/GPS实测穿刺点数据的建模方法，利用本文建模方法计算获得的垂直总电子含量（VTEC）值对缺乏实测穿刺点的区域精度有明显的提升.      

基于ADS-B的航空器测高系统误差评估方法

针对基于广播式自动相关监视(ADS-B)数据的航空器高度保持性能监控中测高系统误差准确评估问题,提出了基于核平滑和混合正态分布模型的数据平滑和拟合分析方法。提出了ADS-B信息低分辨率高度数据的核平滑方法,通过比较分析得到了数据平滑的最优窗宽,基于实测数据的分析证明了该方法对于航空器测高系统误差评价的有效性。针对航空器使用的2套独立的测高学设备具有不同的高度保持性能分布特征的问题,提出了基于混合正态分布模型的拟合分析方法,实测结果表明,该方法可以准确拟合航空器测高系统误差的双峰特征。本文所提出的方法已经在中国RVSM航空器高度保持性能的实际分析中使用,分析结果满足国际民航组织的相关要求。     

短波射线追踪技术中的电离层混合建模方法

在国际参考电离层模型和多层准抛物模型的基础上,提出了一种混合应用两种模型进行电离层建模的新方法.利用射线追踪技术,分别对混合模型和传统国际参考电离层模型下短波射线在电离层中的轨迹进行了仿真,得到了电波群路径.通过与实测电波群路径的对比,结果表明:对中国中纬度地区在电离层混合模型下的射线追踪精度优于传统国际参考电离层模型下的射线追踪精度,同时混合建模方法降低了多层准抛物模型对输入条件的要求,扩展了多层准抛物模型在射线追踪技术中的应用范围.     

利用GPS技术实时监测上海区域电离层变化

基于GPS技术实时监测电离层变化原理, 利用载波平滑伪距观测值建立区域电离层模型的方法, 计算了电离层延迟量和硬件延迟, 根据硬件延迟值相对稳定的特点, 采取一定时段求解出硬件延迟量, 对实时硬件延迟量进行预报, 进而实时分离GPS信号传播路径上的垂直总电子含量VTEC. 利用上海区域内的GPS网的观测数据, 建立实时上海区域电离层延迟模型, 监测上海区域的电离层变化. 数据分析结果表明, 这种方法的内符合精度优于3 TECU.      

一种基于系数择优的低阶球谐电离层延迟改正模型

针对单频接收机的电离层延迟改正问题, 提出了一种基于系数择优的低阶球谐电离层延迟改正模型. 按照电离层延迟改正模型参数择优问题的描述, 明确参数优化的目标和约束条件, 根据参数选择可编码的特点, 提出了利用遗传算法进行参数择优的方法及步骤. 以欧洲定轨中心(CODE)提供的电离层数据作为参考标准, 对参数择优模型、 低阶球谐模型和Klobuchar模型模拟的区域电离层VTEC精度进行了比较分析. 结果表明, 较之相同系数个数的低阶球谐模型, 参数择优模型精度平均改进了1～2TECU, 而且比Klobuchar模型及低阶球谐模型能更好地反映电离层的周日变化及纬度变化特征.      

Klobuchar模型的实用分析与改进

电离层延迟误差是无线电信号传播中不可忽视的误差源.GPS特许用户利用双频接收机的双频观测值直接对电离层延迟进行实时测定,其所得结果精度很高.多数普通用户所使用的单频接收机依靠电离层模型对其进行误差修正,效果不很理想.本文通过WUHN观测站双频接收机10天的实测数据对GPS广播星历采用的Klobuchar模型进行了验证,其结果与前人论述相一致.此外,经由反映太阳活动强度的太阳相对黑子数对Klobuchar模型提出了新的改进方法.实验数据结果表明,该方法对此模型修正效果有大幅提升,对原模型修正效果>50%的修正率由60%左右提升至85%以上,>80%的修正率由10%左右提升至40%以上.在实际应用中单频接收机用户可以参考本文改进方法对Klobuchar模型进行修正.      

神经网络在导航卫星钟差预报中的应用CSCD

为提高导航卫星钟差预报精度,提出一种神经网络和多项式相结合的钟差预报方法,该方法在根据星载原子钟物理特性进行多项式模型预报后,采用神经网络对多项式模型预报误差进行建模,以实现导航卫星钟差预报精度补偿。为验证本文提出的预报模型的可行性和有效性,利用实测的COMPASS导航卫星钟差数据进行钟差预报精度分析,并与传统的多项式模型预报精度进行比较。结果表明:基于神经网络建立的组合预报模型能有效提高导航卫星钟差的预报精度。     

连续波雷达测量数据随机误差处理方法研究

针对差分方法和最小二乘法在处理连续波雷达跟踪数据的随机误差时,处理结果常常出现不一致的情况,对这两种方法的内在联系进行了深刻的研究,首次证明了“ｋ阶差分与ｋ＋１个点的ｋ－１次多项式的平滑残差具有完全相同的频谱特性”。针对雷达测量数据中随机误差时序相关性较强的实际情况,导出了相关条件下差分步长的计算公式,最后,提出了高精度分离数据中随机误差的非线性自由节点样条函数方法,该方法经仿真和大量实测数据处理     

基于GPS信号的电离层S4指数计算方法研究

电波穿越电离层时,由于受到电离层不均匀结构的影响,电波的幅度、相位、时延等有时会发生快速抖动,这就是所谓的电磁波电离层闪烁现象.电离层闪烁会影响卫星通信系统的质量和导航系统的精度.本文分析了GPS信号研究电离层闪烁的基本原理,讨论了电离层闪烁监测中S4指数的计算方法及其修正方法.通过数据模拟,评估了原始S4指数计算方法及其修正方法的性能特点.针对原始S4指数计算方法及修正方法的不足,提出了一种新的修正方法,并采用实测GPS数据对上述方法进行了检验.结果表明,上述方法是有效的和可靠的.      

基于北斗GEO卫星双频观测值连续监测电离层延迟

利用北斗GEO卫星观测数据直接计算电离层延迟。由于GEO卫星具有固定穿刺点和静地的特性,使得观测站监测电离层变化时可不考虑空间变化,并可进行连续不间断监测。通过分析北斗GEO卫星三种频率码伪距和载波相位观测值不同组合,选取B1&B2双频计算电离层延迟为最优组合,采用相位平滑伪距的方法计算电离层延迟TEC,相较其他电离层模型,该方法的优点是不会引入模型误差,可得到连续的高精度的电离层延迟监测结果。     

The spatio-spectral localization approach to modeling VTEC over the western part of the USA using GPS observations

The precise ionosphere modeling is crucial and remains a challenge for GPS positioning and navigation, as well as many other Earth observation systems. In this research, two approaches have been proposed to model the vertical total electron content (VTEC) of the ionosphere using spherical slepian function. For the two-dimensional case, VTEC has been modeled in a sun-fixed reference frame and the three-dimensional approach based on the system of the three-dimensional base functions has been defined as the tensor product of the spherical slepian function for the longitude and latitude in an Earth-fixed reference frame, and the polynomial B-spline function for time. Rather than the spherical harmonics, the spherical slepian functions can be employed to produce the locally and globally orthogonal bases to optimally represent the data in any arbitrary region up to a given degree. The spherical slepian functions have been applied to the real data obtained from the ground-based GPS observation across the western part of the USA.     

Adaptation of the bottomside electron density profile of the IRI model to data of topside radiosounding

A method is proposed for reconstructing the electron density profiles N(h) of the IRI model from ionograms of topside satellite sounding of the ionosphere. An ionograms feature is the presence of traces of signal reflection from the Earth's surface. The profile reconstruction is carried out in two stages. At the first stage, the N(h) –profile is calculated from the lower boundary of the ionosphere to the satellite height (total profile) by the method presented in this paper using the ionogram. In this case, the monotonic profile of the topside ionosphere is calculated by the classical method. The profile of the inner ionosphere is represented by analytical functions, the parameters of which are calculated by optimization methods using traces of signal reflection, both from the topside ionosphere and from the Earth. At the second stage, the profile calculated from the ionogram is used to obtain the key parameters: the height of the maximum hmF2 of the F2 layer, the critical frequency foF2, the values of B0 and B1, which determine the profile shape in the F region in the IRI model. The input of key parameters, time of observation, and coordinates of sounding into the IRI model allows obtaining the IRI-profile corrected to real experimental conditions. The results of using the data of the ISIS-2 satellite show that the profiles calculated from the ionograms and the IRI profiles corrected from them are close to each other in the inner ionosphere and can differ significantly in the topside ionosphere. This indicates the possibility of obtaining a profile in the inner ionosphere close to the real distribution, which can significantly expand the information database useful for the IRTAM (IRI Realmax Assimilative Modeling) model. The calculated profiles can be used independently for local ionospheric research.     

The investigation of the ionospheric variability by the radiotranslucence method

To provide a continuous single-point sounding of a large-scale region of the ionosphere the translucence method of studying the ionosphere utilizing satellite navigation system signals has been used. Simultaneous receiving the signals of GPS Navstar and GLONASS from different azimuths gives information on variations of the ionosphere in almost real time. Using measured data the reconstruction of the electron density profiles in the regions of intersection of a sounding ray with the ionosphere has been carried out. The translucence method was used to investigate the ionosphere effects of a partial solar eclipse (PSE) that occurred on 11.08 1999 by probing of the ionosphere with different GPS system signals in the Zwenigorod region.     

Numerical study of traveling ionosphere disturbances with vertical incidence data

High frequency ionosphere vertical sounding, as an important and representative application for detecting the ionosphere and studying the characteristics of radio propagation, can be utilized to monitor the ionosphere continuously variation and to acquire the ionosphere asymmetrical features of diverse scale above the ionosphere vertical sounding stations. This is a first article on real time application of numerical methods to obtain the parameters of traveling ionosphere disturbances (TIDs) using vertical incident ionograms. In this paper, the distribution of ionosphere electron density with TIDs is constructed using a background ionosphere model superimposed a perturbation theory model. The background ionosphere electron density is modelled by the inversion of vertical incident ionograms which are observed before the appearance of the disturbance. Based on the fourth order Adams-Bashforth-Moulton (the so-called ABM) predictor corrector method, instead of Runge-Kutta method, the fast digital ray tracing method is established. According to process of the disturbed trace simulation and parameters inversion, the characteristic parameters of ionosphere disturbance at different detection time can be obtained in real time. The numerical analysis of TIDs is then captured completely.     

电离层Es对HF和VHF传播信号的影响

Es层是存在于电离层中的电子密度非常高的偶发E层（Sporadic E）,其电子密度可达常规E层的100倍.电离层Es能够反射原本穿透F层的VHF低频段（30~150MHz）无线电波,而且对HF高频段（10~30MHz）无线电波传播具有显著影响.运用垂测和斜测观测数据,研究HF频段Es层电波传播特征,得到了不同类型及不同高度Es层的衰减系数.根据f₀E_s的日变化规律,可得HF频段衰减系数的日变化规律,进而分析并得到Es层对短波传播的影响.不存在电离层Es时,通常无法通过电离层实现VHF超远距离通信.为了对VHF链路通过电离层Es的传播衰减进行定量分析,根据EBU多条链路的观测结果,拟合并建立了电离层Es衰减模型.将该模型、ITU模型和观测数据进行对比,发现本文建立的模型准确度更高.利用建立的模型,对电离层Es不同临频f₀E_s条件下接收信号场强和电压随传播距离的变化进行了计算,结果可为VHF链路设计及建立提供参考.      

VLF电波渗透到卫星高度电离层传播的全波计算

考虑斜向地磁场的影响将电离层设为多层水平分层各向异性有耗介质, 利用传播矩阵法求解全波方程, 进而研究分析VLF频段电离层反射系数随电波频率的变化, 电离层中两种特征极化波的折射和极化特性, 两特征波的电磁场水平分量以及坡印廷能流密度随传播高度的变化. 数值计算结果表明, 地—电离层波导中的垂直极化波比平行极化波易渗透进入电离层; 电离层中两种特征极化波可分为左旋和右旋圆极化波, 左旋分支由于D层强吸收作用表现为速衰减模, 而右旋分支表现为可传播模, 在传播过程中电磁波的能量主要存储在磁场中; 电波频率越低, 其在电离层中的传播损耗越小. 由数值模拟结果发现, 卫星监测VLF频段的低频部分及更低频段的水平磁场变化对于发现地震电离层电磁前兆异常可能更为有效.      

Validation of the Neustrelitz Global Model according to the low latitude ionosphere

Empirical modeling including empirical model for the total electron content (TEC) is important for the study of the ionosphere and practical applications. In this paper goodness of new Neustrelitz Global Model (then NGM) at low latitudes is studied. The NGM model includes such parameters as the maximal electron density (NmF2) and altitude of the maximum (hmF2). As of today, besides NGM there are several empirical models for NmF2 and hmF2. Therefore, a comparison of these parameters of the NGM model, not only with the experimental data, but also with two versions of the International Reference Ionosphere (the IRI model): IRI2001 and IRI-Plas would be instructive. Because the NGM model incorporates special factor describing the equatorial anomaly, the comparison in lower latitude areas is particularly interesting. As one can see from the presented example of the data from low latitude stations located in the northern and southern hemispheres near the Greenwich meridian, the NGM model may have certain advantages over the IRI model versions. In particular, NGM TEC is preferable regardless of solar activity level while NGM NmF2 is only preferable under high solar activity conditions. Next, NGM equivalent slab thickness of the ionosphere: τ(NGM) = TEC(NGM)/NmF2(NGM) has been calculated and tested to answer the question whether τ(NGM) can be used as a proxy of the slab thickness of the ionosphere for an empirical modeling. The answer is positive for the near equatorial stations and periods of high solar activity, and under such conditions predicted τ(NGM) can be used for deriving NmF2 from the experimental values of TEC(CODE) in real time.     

海南地区电离层Es特性研究

利用中国科学院空间科学与应用研究中心海南电离层观测站DPS-4电离层测高仪2002年3月至2005年2月的观测数据,对太阳活动下降期间海南地区上空发生的偶发E层(Es)的逐年变化和季节变化进行了统计分析.主要结果表明,在这3年中海南地区Es事件出现次数逐年增加;Esr,Esq出现最频繁,其次是Esr,而Esc和Esf出现次数较少,出现次数最少的是Esh;Es事件在夏季出现最为频繁,秋季和冬季次之,春季最为稀少;各季节不同类型Es事件的出现率也不同,其中Esl和Esq一般在各季节占主导地位,Esr其次,Esc,Esf和Esh出现次数较少,尤其是Esf在秋季几乎没有出现.这些结果对于进一步研究Es产生的物理机制提供了探测基础,同时对于电离层空间天气预报模型的建立也具有重要的意义.      

A MARS-based method for estimating regional 2-D ionospheric VTEC and receiver differential code bias

The geometry-free linear combination of dual-frequency GNSS reference station ground observations are currently used to build the Vertical Total Electron Content (VTEC) model of the ionosphere. As it is known, besides ionospheric delays, there are differential code bias (DCB) of satellite (SDCB) and receiver (RDCB) in the geometry-free observation equation. The SDCB can be obtained using the International GNSS Service (IGS) analysis centers, but the RDCB for regional and local network receivers are not provided. Therefore, estimating the RDCB and VTEC model accurately and simultaneously is a critical factor investigated by researchers. This study uses Multivariate Adaptive Regression Splines (MARS) to estimate the VTEC approximate model and then substitutes this model in the observation equation to form the normal equation. The least squares method is used to solve the RDCB and VTEC model together. The research findings show that this method has good modeling effectiveness and the estimated RDCB has good reliability. The estimated VTEC model applied to GPS single-frequency precise point positioning has better positioning accuracy in comparison to the IGS global ionosphere map (GIM).