基于频域GPS信标提取电离层闪烁信息的方法

GPS(global positioning system)信标提取电离层闪烁信息的传统方法十分依赖于GPS硬件接收机对电离层闪烁信号的连续捕获和准确跟踪,而电离层闪烁发生特别是强闪烁情况下信号往往很弱,极易发生接收机的信号失锁,导致闪烁信息丢失的现象.针对这一问题,以构建软件GPS接收机为基本前提,提出一种基于快速傅里叶变换的频域处理方法用于计算电离层幅度闪烁指数.模拟计算结果表明:新方法计算得到的闪烁指数避免了系统误差,具有较高的精度.     

低纬电离层闪烁对GPS观测值及其导航定位的影响

电离层闪烁对全球定位系统(GPS)的影响已经被认为是GPS现代化后面临的主要问题.利用低纬地区电离层闪烁监测接收机(18.34°N, 109.62°E)在2012-08-01～31的GPS闪烁数据和观测数据,开展了电离层闪烁对GPS观测值及单点定位的影响研究.研究结果表明,电离层闪烁可以导致GPS卫星信号发生衰减,最大衰减幅度达20 dB-Hz;相比于GPS L1观测值,电离层闪烁对GPS L2影响更大;电离层闪烁可导致周跳的发生,统计表明,每100个强电离层闪烁事件(S_40.5)可以导致21个周跳发生,而100个弱电离层闪烁事件(0.2S_4≤0.5)仅导致6个周跳发生;强电离层闪烁环境下,卫星信号会遭遇失锁现象,从而破坏卫星几何分布结构,导致GPS导航定位性能降低;相比正常的电离层环境,电离层闪烁活跃环境下的GPS单点定位精度降低了23%.     

电离层闪烁下4路信号处理的载波锁相环

针对电离层闪烁导致的卫星导航接收机载波锁相环失锁问题,提出一种基于Kalman滤波器的4路信号处理载波锁相环. 该环路通过增加两路信号处理对锁相结果进行纠正,扩大了锁相环的相位牵引范围,同时根据信号实时载噪比自适应调节滤波系数,有效避免电离层闪烁时信号振幅衰落和相位突变引起的环路失锁. 通过仿真表明,这种锁相环可以在持续中强度和瞬时高强度的电离层闪烁下保持跟踪.      

基于GPS数据确定电离层延迟的蚀因子法

通过建立电离层交叉点(ionospheric pierce point,IPP)点的电离层蚀因子(ionospheric eclipse factor,IEF)λ及其影响因子(ionospheric influence factor,IFF)-λ,综合λ,-λ与IPP点的地方时t,研究了一种利用GPS数据确定电离层延迟的新方法--电离层蚀因子法(ionospheric eclipse factor method,IEFM).IEFM方法强调根据电离层的变化特性选择合理的TEC模型.初步结果表明,利用IEFM拟合的电离层延迟的改正精度更接近L3观测自校正电离层延迟的精度.     

电离层闪烁对GEO SAR成像的影响分析

研究电离层闪烁效应对GEO SAR成像的影响. 针对GEO SAR系统的特点,首先通过GEO SAR系统参数的仿真,分析电离层对于GEO SAR影响的特殊性,而后通过多相屏理论,仿真分析电离层闪烁产生的随机起伏现象对GEO SAR系统图像质量的影响,最后结合Monte Carlo仿真,给出了不同电离层起伏条件下GEO SAR直接合成孔径处理的最优积累时间. 分析结果表明:相同GEO SAR系统参数下,电离层闪烁起伏越大,合成时间越长,成像质量结果越差,甚至会出现无法聚焦的情况.      

基于单站GPS数据的GPS系统硬件延迟估算方法及结果比较

从GPS数据中解算电离层总电子含量(TEC)的最大误差源是硬件延迟。作者介绍了两种解算电离层TEC和硬件延迟的方法。利用单站的GPS双频数据,计算了2004年电离层TEC和硬件延迟,对两种方法得到的硬件延迟进行了比较,并且和欧洲定轨中心的公布结果进行了对比,同时分析了不同纬度台站数据解算硬件延迟的误差特点。结果表明：这两种方法均可以解算TEC和硬件延迟,结果是可靠的。解算的硬件延迟的标准偏差与观测站的纬度有关,在中国区域,纬度越低,估算的硬件延迟偏差越大,对这一情况进行了分析。     

电离层对GPS测量的影响

GPS作为一种无线电导航系统,受到很多误差源的影响,即:卫星轨道误差、卫星钟差、电离层延迟误差、对流层延迟误差、多路径误差、接收机钟差和测量噪声等误差。其中,自从SA(Selected Availability)于2000年5月1日取消以后,电离层误差是最大的一项误差。电离层延迟对GPS定位的影响结果,主要体现在定位精度的降低和定位方法的限制等方面。电离层使接收到的GPS信号产生延迟,从几米到百米以上。如果不考虑这种影响,就会严重降低GPS定位和授时的精度。因此,电离层误差是GPS测量中的主要误差源,必须加以改正。本文介绍了电离层对GPS定位的影响,包括码群延迟(即绝对测距误差)、载波相位超前(即相对测距误差)、多普勒时延(即距速误差)以及信号衰减(即振幅闪烁),并论述了影响电离层密度的因素。     

低地磁扰期间海南电离层F2层临界频率的观测与IRI预测结果的对比研究

国际参考电离层模型(IRI)是非常有影响的电离层经验模型之一,利用该模型对我国东亚地区,尤其是海南低纬度地区,进行长期预测的效果尚未研究。通过对一个太阳活动周(2002~2012年)期间海南观测站(19.5°N,109.1°E)数字测高仪DPS-4D观测到的电离层临界频率foF2在低地磁扰动条件下的月中值日变化、季节变化和年变化进行了分析;并与相应的IRI-2012模型预报值进行了对比研究。结果表明:1观测到的foF2存在着明显的冬季异常和半年异常现象,对太阳活动存在着明显的依赖关系;2IRI-2012模型预报值虽给出了海南foF2的基本观测特征,但细节上IRI模型预测值与观测值还是存在着地方时、季节和年度偏差,主要表现为:在太阳活动低年模型存在高估;在太阳下降年期间模型存在低估;在太阳活动较高时期模型存在明显的分季低估,冬、夏季高估;整体上,多数偏差率在±20%以内。偏差率较大的时段主要集中在0500-0800LT,这与以前研究结果基本一致。这些结果对进一步完善IRI模型,尤其是在中国低纬度地区foF2预测参数方面,具有重要的参考价值。     

电离层对耀斑响应的GPS观测研究

利用1997～1999年全球日地电离层观测卫星的耀斑观测资料以及全球定位系统(GPS)网的观测资料,对不同级别耀斑爆发期间的电离层总电子含量(TEC)随时间的变化特点、TEC增幅及其与X射线最大辐射通量之间的关系进行了研究.利用缓变型耀斑爆发期间的GPS观测数据,分析了电离层对此类耀斑的响应特点.     

太阳高年期间海南电离层扩展F出现的起始时间研究

电离层扩展F与电离层闪烁现象密切相关,它们出现的起始时间存在着很大程度上的一致性,因此研究电离层扩展F出现的起始时间将对闪烁预报模型的建立具有重要的应用价值.将太阳高年（2002年3月-2003年2月）期间海南地区DPS-4测高仪观测到的扩展F按照频率、区域、混合和强区域扩展等分为四种类型,对其出现的起始时间进行了分析研究.结果表明：频率扩展和混合扩展的起始时间分别集中在0200LT-0800LT和0000LT-0600LT;而区域扩展和强区域扩展出现的起始时间分别集中在2000LT-0200LT和2000LT-2200LT.     

Spectra of L-band ionospheric scintillation over Nanjing

We report the spatiotemporal statistical characteristics of amplitude scintillation over Nanjing.A FFT method for computing scintillation intensity power spectra is briefly described.Using this method,the data with ISATM in Nanjing is analyzed.Spectra characteristic is presented and the irregularities property is discussed preliminarily.The results reveal that the power spectra obtained for Nanjing is consistent with theoretical modeling.At frequencies below the Fresnel frequency,the power density plotted on log-log scale is almost constant whereas above it asymptotes to a straight line.The spectral index ranges from 1.71 to 1.92,which has positive correlation with the S 4 index.Finally,the average drift velocity of irregularities is computed assumably and compared with that obtained for Xinxiang and Haikou.     

Development of an ionospheric scintillation monitor using single frequency GPS receiver

Besides their intended use in radio navigation, global positioning system (GPS) satellite signals provide convenient radio beacons for ionospheric studies. Among other propagation phenomena, the ionosphere affects GPS signal propagation through amplitude scintillations that develop after radio waves propagation through ionospheric electron density irregularities. This paper outlines the design, testing, and results of a specialized GPS receiver to monitorL-band scintillations. The scintillation monitor system consists of a commercial GPS receiver development kit with its software designed to log signal strength and carrier phase from up to 12 channels at one sample per second rate. Other prime features of the monitor include the data compression transmission and processing. Here is the fact that they are inexpensive and compact and therefore can be readily proliferated. Foundation item: Supported by the National Natural Science Foundation of China (No. 49984001) Biography: Shu Di-fei (1973-), male, Master candidate, research direction: studying ionosphere on GPS beacons.     

Climatological analysis and modeling of the ionospheric global electron content

In this paper, we calculate the ionospheric global electron content （GEC） from the GPS TEC data along the geographic longitude 120°E during the period of 1996-2004, and investigate the relationship between GEC and 10.7 cm solar radio flux F10.7 and its seasonal dependence with partial correlation analysis. Our results show that GEC is closely correlated with solar activity index F10.7 and is also related with annual and semiannual variations. An empirical GEC model driven by those factors is then to examine the influences of different solar activity proxies for the model input. The results suggest that GEC mainly depends on solar activity and the seasonal variations; the latter is also modulated by solar activity. Furthermore, the magnitude of semiannual variation is a little greater than that of annual variation. Our empirical GEC model is proved to be better than the model proposed by Afraimovich et al.     

A theoretical model for mid-and low-latitude ionospheric electric fields in realistic geomagnetic fields

The geomagnetic fields, which play important roles in the ionospheric dynamo, can greatly affect the global distribution of ionospheric electric fields, currents and other ionospheric electrodynamics phenomena. In the study of ionospheric electrodynamics phenomena, such as the longitudinal variations of ionospheric electric fields, the non-dipolar component of the geomagnetic fields must be taken into account. In this paper, we deduce a theoretical electric field model for ionospheric dynamo at mid- and low-latitude which adopt a modified magnetic apex coordinates system. In the new electric field model, the geomagnetic fields can be calculated from either the IGRF model or the dipole field model, and the neutral winds and conductivities are calculated based on empirical models. Then the dynamo equation for the electric potential is finally solved in terms of the line-by-line iteration method, and the ionospheric electric fields and currents are derived from the calculated potential. Our model can reproduce the main features of the ionospheric electrodynamics processes, so it will be a useful tool for the investigation of the upper atmosphere and ionosphere.     

Analysis and correction for systematic error of ionospheric monostatic system

In the ionospheric monostatic system the echo is affected by systematic error. A real-time method using the special characters of direct wave existing in monostatic radar to correct systematic error is advanced. In the condition of large-amplitude direct wave, time delay of maximum amplitude of echo is considered as system time delay; in the condition of small-amplitude direct wave, the mathematical model of time delay error is built to approach after direct wave test. And a method using large-amplitude direct wave to correct phase distortion is advanced. It achieves good effect using this method in practice, which can improve the quality of sound result obviously. Biography: WANG Feng (1982–), male, Ph. D. candidate, research direction: radar signal processing and radar software system design.     

行星际闪烁（IPS）观测中的几个问题

行星际闪烁和电离层闪烁的强度功率谱覆盖的主要频段是不同的,因此可以区分．本文给出了行星际闪烁观测中电磁波频率与对应的弱散射最小日心距之间的定量关系式,以及闪烁指数随射电源日张角变化的曲线方程,并与观测事实进行了比较．     

GBAS中相位平滑伪距差分修正改进算法

针对卫星导航精度问题,提出一种载波相位平滑伪距差分修正算法的改进方案.通过无码载偏离平滑滤波技术来解决电离层对伪距和载波相位观测值带来的不一致性导致的电离层误差加剧问题.利用信号传播中误差模型预测值、载波信号和码伪距确定滤波器的衰减因子,把接收到的双频载波信号相位值和伪距值线性组合,输入滤波器滤波.同时用卫星修正信息对平滑伪距值中钟差进行修正.仿真结果表明通过该算法能够减少滤波后的信号残差,提高载波相位平滑伪距差分修正值标准差的可用性,减少电离层误差对星基导航精密进近阶段定位精度的影响.     

BD星基增强系统格网电离层延迟算法的研究

随着北斗卫星导航系统的发展日益成熟,开发基于北斗的星基增强系统已刻不容缓,而电离层误差是影响星基增强系统定位精度的重要误差源。利用中国大陆构造环境监测网络的10个GNSS参考站在2016年3月20日的观测数据,验证了基于北斗导航系统的星基增强系统格网电离层修正算法在中国地区部分站点的修正精度,与Klobuchar模型修正法进行了对比,并检验了格网电离层垂直延迟的修正误差GIVE。结果表明,格网电离层修正算法的修正精度普遍优于Klobuchar模型修正法;修正误差也在正常范围内,进一步说明格网电离层延迟算法在中国地区的应用是可行的。