穿过电离层电子密度不均匀体的脉冲平均到达时间

本文利用前向多重散射理论的新进展，推导了穿过电离层电子密度不均匀体脉冲平均到达时间的理论计算公式，其中包括背景介质折射效应的贡献、色散效应的贡献、电离层电子密度不均匀体的散射效应的贡献和色散效应的贡献，在水平分层背景电离层和高频近似的情况下，给出了背景电离层折射效应、一阶色散效应、电子密度不均匀体的散射效应和一阶色散效应对对称脉冲平均到达时间影响的计算公式。针对特定的电离层情况，分别计算了上述几种     

电离层不均匀性对GPS系统的误差影响分析

在ＧＰＳ定位误差分析中，对电离层误差大多只考虑了折射效应，采用双频技术即可消除折射一阶项的影响，更进一步的误差分析通常是考虑电离层折射的高阶项（主要是二阶项）。但均未考虑电离层不均匀性对ＧＰＳ系统误差的影响。本文根据波在电离层随机介质脉冲平均到达时间的理论结果，对ＧＰＳ信号穿越电离层的情况进行了模拟计算，在得出了典型背景电离层参数条件下折射一阶项、二阶项引起的ＧＰＳ信号延迟误差的基础上，重点讨论了     

背景各向异性不均匀的随机起伏电离层中高频电波散射的几何光学近似

本文讨论了背景为各向异性、不均匀的随机起伏电离层中高频电波的传播和散射问题。在几何光学近似下，给出了电子浓度不均匀体散射引起的高频电波的相位与振幅的起伏，并在此基础上，讨论了起伏的统计特性。结果表明，由各向异性引起的侧向偏移与极化效应对高频电波波场的起伏有显著的影响，往往不能忽略。     

Experimental observations of carrier phase acceleration in conditions of polar ionosphere

The paper presents a comparative analysis of the quality of measuring the phase carrier of signals from GLONASS and GPS navigation satellites and spectrum of small-scale irregularities of electron density in conditions of a nonstationary and inhomogeneous polar ionosphere. It is shown that small-scale irregularities of the electron density in the ionosphere can lead to a substantial nonstationary increase in the acceleration of the phase carrier of both GPS and GLONASS by a factor of 1.3–2.5 from the background level.     

Distortions of the low frequency signal by Martian ionosphere at vertical propagation

A mathematical tool is described that takes into account signal distortions caused by phase dispersion and signal absorption in the Mars ionosphere during reflection from the Mars surface below the orbiter. This tool is used to estimate the distortion of the cross-correlation function by phase dispersion and signal absorption caused during a double traverse of the radio signal through the Mars nighttime ionosphere on frequencies used for the radar experiment MARSIS. Ionospheric absorption reduces the cross-correlation function distortions caused by ionospheric dispersion. It is shown, that the value of signal absorption depends on free electron number density in the lower part of an ionosphere.     

天波雷达电离层相位污染模式认知与分析

电离层相位污染模式认知是天波超视距雷达电离层污染校正准确性的基础。由于电离层的复杂性和模式的不准确性，已有算法在实测数据处理中校正效果不佳。为了提高电离层相位污染校正的准确性，对电离层相位污染模式的分类开展研究，给出电离层相位污染统一模型，分析了3种不同模式的电离层相位污染对海杂波回波多普勒谱一阶Bragg峰的影响，仿真分析验证了3种相位污染均使海杂波回波多普勒谱一阶Bragg峰展宽，将纯正弦模式的相位污染进一步细化分类，为电离层相位污染的分类校正方法研究提供参考。     

应用武汉电离层斜向返回探测系统测量回波相位

电离层作为时空随机变化介质,除了规则变化外还存在着不规则结构和随机变化,即电离层不稳定性,其直接影响是经过电离层传播的电波产生相位随机起伏.利用垂测仪和信标接收机测量精确相位数据的各种方法已被广泛应用,而应用具有大范围电离层探测能力的高频天波超视距雷达测量回波相位的方法还没有文献提出.文中提出了一种从相位编码脉冲压缩体制电离层探测雷达测量的电离层信道双时响应中提取相位数据的理论.此理论被成功地应用于自行研制的武汉电离层斜向返回探测系统中,探测获得了有效的回波相位数据.     

Development and use of a GPS ionospheric scintillation monitor

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 propagate through ionospheric electron density irregularities. This paper outlines the design, testing, and operation of a specialized GPS receiver to monitor L-band amplitude scintillations: the Cornell scintillation monitor. The Cornell scintillation monitor consists of a commercial GPS receiver development kit with its software modified to log signal strength from up to 12 channels at a high data rate (50 samples/s). Other features of the receiver include the optional assignment of a channel to monitor the receiver noise level in the absence of signal tracking and the means to synchronize measurements between nearby independent receivers to perform drift measurements and correlation studies. The Cornell scintillation monitor provides characterization of the operational L-band scintillation environment and additionally permits study of the multipath environment of a static antenna, GPS scintillation monitors can provide information about the state of ionospheric irregularities for pure research purposes as well. Their strength lies in the fact that they are inexpensive and compact and therefore can he readily proliferated. Even a single scintillation monitor can supplement radar spatial coverage of irregularities in a limited way because it monitors several satellite lines of sight simultaneously     

基于多手段观测的海口站电离层闪烁对地磁暴响应研究

联合利用CHAMP卫星等离子体密度就位观测数据和海口站GPS电离层闪烁监测仪数据，分析了2004年1月、2月和11月三次地磁暴期间海口站的电离层闪烁特征.我们发现海口站电离层对3次磁暴事件的响应特征明显不同.就磁暴期间B_z分量和Dst指数的观测值来说，2004年11月的磁暴事件最强，其次是1月的，2月的最弱.而地基闪烁监测仪的观测结果表明:1月磁暴事件期间，L波段电离层闪烁最强，闪烁指数S₄最大值接近于1.0，闪烁出现率的最大值超过80%；2月磁暴事件期间，电离层闪烁持续时间最长，S₄最大值接近于1.0，闪烁出现率的最大值接近63%；11月磁暴主相和恢复相期间，无电离层闪烁现象出现.CHAMP卫星和地面闪烁监测仪观测到的结果一致，表明多重尺度的电离层不均匀体通常同时存在，但是小尺度的电离层不规则体通常会先消失.对比上述三次实验的观测结果，我们推断造成电离层响应特征差异的原因与环电流的影响有关，Aarons准则可较好地解释电离层对3次磁暴事件的响应.同时跨赤道风场可能也有贡献，它通过增加沿场向积分的Pedersen电导率，降低了R-T不稳定性，从而抑制了电离层闪烁的发生.     

Investigation of the parameters of signals reflected from the ionosphere on the basis of regular radio-field measurements performed in the long-wave band

Diurnal and seasonal variations of the signal reflected from the ionosphere are investigated on the basis of regular measurements of the amplitude and phase of the radio field of a reference radio station operating at a frequency of 50 kHz. The reflected signal is extracted from the mixture of the ground-wavel and reflected-wave fields using a special procedure. Effective parameters of an exponential ionospheric model, which characterize the statistical parameters of the signals in the long-wave band at medium distances, are proposed.     

电离层色散效应对宽带BOC信号的影响

电离层色散特性导致宽带二进制偏移载波(Binary Offset Carrier,BOC)信号的码片时域波形和相关函数曲线产生畸变,影响BOC信号完好性和跟踪性能。为了评估电离层对BOC信号传输的影响,构建了宽带BOC信号的电离层影响分析框架,分析了电离层色散效应对码片时域波形和相关特性的影响,并评估了三类典型BOC信号的带内电离层色散效应在码跟踪环路和载波跟踪环路引入的偏差。研究结果表明,电离层色散效应会导致宽带BOC信号时域码片实部和虚部边缘产生抖动现象,色散信号与标准信号间的互相关函数会产生明显的相关损耗;在电离层活跃期间,电离层色散效应在码跟踪与载波相位跟踪中均引入明显的鉴别误差。该结果对BOC信号的电离层误差的评估与校正有一定的参考意义。     

A Study of Signal Decorrelation Through the Ionosphere

Signals in a satellite-earth communication link pass through the ionosphere where there may exist random irregularities. These random irregularities will scatter and distort the Signal, producing a fading channel. Such a channel is generally characterized by the symmetric and asymmetric correlation functions. Approximate solutions for these functions have been obtained and the results plotted for typical ionospheric parameters. Some of the results are shown in terms of coherence bandwidth.     

天波雷达电离层污染校正与海杂波抑制

在天波超视距雷达（OTHR）中,舰船目标的多普勒频率与海杂波谱接近,电离层污染会导致海杂波频谱展宽,从而淹没邻近的舰船目标信号。考虑到电离层污染会导致OTHR回波信号的相位缓慢变化,提出了采用相位梯度法对回波信号进行电离层污染校正;利用污染校正后的海杂波可以近似为两个单频信号之和这一特点,提出了应用奇异值分解来实现对海杂波的抑制。仿真结果表明,文中算法可以有效地校正电离层污染,抑制海杂波,显著提高信杂比,从而有效解决强海杂波对舰船目标的遮蔽问题。与现有的HRR—SVD算法相比,文中算法可以适用于相干积累时间较长和电离层污染较大的情况,防止残留的海杂波形成虚警,提高了OTHR对海杂波附近舰船目标的检测能力。     

Potential Accuracy of Estimation and Compensation of Ionospheric Errors of Radar Measurements of the Ranges of Space Objects Using Chirp Pulses

The expression for the complex envelope of the reflected chirp pulse at the input of the radar receiver is derived taking into account the dispersion distortions in the ionosphere in the geometric optics approximation. The relations for the lower limits of the rms values of fluctuation errors of estimates of the radar range and the ionospheric correction as functions of the signal-to-noise ratio, the wavelength, and the relative deviation frequency are obtained. The possibilities of refinement of estimates of the ionospheric correction with the use of empirical models of the ionosphere are considered.     

A method to correct HF skywave backscattered signals forionospheric frequency modulation

A method is described to correct HF signals reflected by the ionosphere and backscattered by the sea surface for ionospheric frequency modulation, which produces spectral-line smearing. The statistical mean of the time derivative of the phase of the signal, weighted by the signal energy, is proposed as an estimator of this modulation. The accuracy of the estimator is measured and the efficiency of the signal processing is tested by synthetically contaminating high-quality signals obtained via sporadic E-layer propagation. Examples of data corrected for F2-layer ionospheric perturbations are shown     

斜入射下电离层闪烁对GEO SAR成像影响分析

本文基于多相位屏理论,研究了电离层闪烁对GEO SAR成像的影响。首先针对电离层各向异性的特点,修正了各向异性电子密度起伏的功率谱,并重新推导了斜入射条件下随机介质中的电磁波传播方程,改进了传统的基于垂直入射和各向同性电离层条件下的多相屏仿真方法,然后结合典型GEO SAR参数,分析了电离层闪烁对GEO SAR成像的影响。最后,通过Monte Carlo仿真,给出了不同电离层电子密度起伏条件下GEO SAR进行合成孔径处理的最优积累时间。分析结果表明,相同GEO SAR系统配置下,电离层闪烁的起伏越大,合成时间越长,GEO SAR成像质量越差,甚至会出现无法聚焦的情况。      

Radio wave scintillations in the ionosphere

The phenomenon of scintillation of radio waves propagating through the ionosphere is reviewed in this paper. The emphasis is on propagational aspects, including both theoretical and experimental results. The review opens with a discussion of the motivation for stochastic formulation of the problem. Based on measurements from in-situ, radar, and propagation experiments, ionospheric irregularities ate found to be characterized, in general, by a power-law spectrum. While earlier measurements indicated a spectral index of about 4, there is recent evidence showing that the index may vary with the strength of the irregularity and possibly a two-component spectrum may exist with different spectral indices for large and small structures. Several scintillation theories including the Phase Screen, Rytov, and Parabolic Equation Method (PEM) are discussed next. Statistical parameters of the signal such as the average signal, scintillation index, rms phase fluctuations, correlation functions, power spectra, distributions, etc., are investigated. Effects of multiple scattering are discussed. Experimental results concerning irregularity structures and signal statics are presented. These results are compared with theoretical predictions. The agreements are shown to be satisfactory in a large measure. Next, the temporal behavior of a transionospheric radio signal is studied in terms of a two-frequency mutual coherence function and the temporal moments. Results including numerical simulations are discussed. Finally, some future efforts in ionospheric scintillation studies in the areas of transionospheric communication and space- and geophysics are recommended.     

Ionospheric modification induced by high-power HF transmitters—A potential for extended range VHF-UHF communications and plasma physics research

When the ionized upper atmosphere of the earth is illuminated by high-power HF radio waves at appropriate frequencies, the temperature of electrons in the ionosphere can be raised substantially. In addition, radio waves with sufficient energy cause parametric instabilities that generate a spectrum of intense plasma waves. Observations of these phenomena have produced new understanding of plasma processes. One consequence of heating and plasma wave generation is that irregularities are formed in the electron distribution which are aligned with the earth's magnetic field. Because of this, a scatterer of large radar cross section is produced, which scatters HF through UHF communication signals over long distance paths, that would not otherwise be normally possible by ionospheric means. This paper summarizes results of radio, radar, communication, and photometric experiments that explored the characteristics of the volume of ionosphere which has been intentionally modified, temporarily, above facilities near Boulder (Platteville), Colo., and at Arecibo, Puerto Rico.     

加热电离层生成不均匀体的理论及模拟研究

针对均匀和平面分层电离层背景,分别建立了描述大功率高频(HF)泵波加热电离层产生不均匀体的物理模型,从理论上解释了加热过程中不均匀体的生成主要是有质动力和热压力共同作用的结果.基于均匀电离层背景下加热电离层生成不均匀体的理论,通过数值模拟得到了加热导致电子密度不均匀体的空间分布.模拟结果表明,电子密度扰动在泵场方向上的特征长度为1km量级,在垂直于泵波电场方向上的特征长度为10～20m;这与电离层加热实验观测到的不均匀体纵向特征长度一般为千米量级、横向特征长度一般为10m量级的结论是相符的.另外,数值模拟得到的电子密度"空洞"和"稠团"的交替分布,可以解释加热过程产生的无线电波自聚焦效应.     

Fluctuations of the group path and the group-delay time of waves obliquely reflected by a plane-layered medium

The spatial correlation properties of the group path and the group-delay time of a radio signal leaving a random plane-layered reflecting medium similar to the ionosphere are considered. The spatial-correlation distances for the group path lying in the incidence plane and oriented perpendicularly to this plane are obtained for various angles of propagation of a wave entering the medium. It is shown that, when a radio signal is scattered by isotropic irregularities of the medium’s permittivity, regular refraction results in anisotropic fluctuations of the signal’s characteristics and the degree of anisotropy grows with the sounding angle.