Ionospheric wave processes during HF heating experiments

Effects of ionospheric modification produced by powerful high frequency radio waves are studied using the method of field-aligned scattering of diagnostic HF radio signals. Observations of scattered HF signals have been made by the Doppler spectrum method. Analysis of the experimental data shows the appearance of quasiperiodic variations in Doppler frequency shift f_d, with periods 30–60 s during the heating cycles. Powerful HF waves are assumed to excite the Alfvén resonator generating oscillations of the magnetic field lines in the heated region and giving rise to f_d artificial variations and magnetic pulsations. In the case of continuous action of the powerful HF transmitter ionospheric waves are sometimes observed with periods 12–25 min, typical of medium-scale travelling ionospheric disturbances.     

The use of ionospheric tomography and elevation masks to reduce the overall error in single-frequency GPS timing applications

Signals from Global Positioning System (GPS) satellites at the horizon or at low elevations are often excluded from a GPS solution because they experience considerable ionospheric delays and multipath effects. Their exclusion can degrade the overall satellite geometry for the calculations, resulting in greater errors; an effect known as the Dilution of Precision (DOP). In contrast, signals from high elevation satellites experience less ionospheric delays and multipath effects. The aim is to find a balance in the choice of elevation mask, to reduce the propagation delays and multipath whilst maintaining good satellite geometry, and to use tomography to correct for the ionosphere and thus improve single-frequency GPS timing accuracy. GPS data, collected from a global network of dual-frequency GPS receivers, have been used to produce four GPS timing solutions, each with a different ionospheric compensation technique. One solution uses a 4D tomographic algorithm, Multi-Instrument Data Analysis System (MIDAS), to compensate for the ionospheric delay. Maps of ionospheric electron density are produced and used to correct the single-frequency pseudorange observations. This method is compared to a dual-frequency solution and two other single-frequency solutions: one does not include any ionospheric compensation and the other uses the broadcast Klobuchar model. Data from the solar maximum year 2002 and October 2003 have been investigated to display results when the ionospheric delays are large and variable. The study focuses on Europe and results are produced for the chosen test site, VILL (Villafranca, Spain). The effects of excluding all of the GPS satellites below various elevation masks, ranging from 5° to 40°, on timing solutions for fixed (static) and mobile (moving) situations are presented. The greatest timing accuracies when using the fixed GPS receiver technique are obtained by using a 40° mask, rather than a 5° mask. The mobile GPS timing solutions are most accurate when satellites at lower elevations continue to be included: using a mask between 10° and 20°. MIDAS offers the most accurate and least variable single-frequency timing solution and accuracies to within 10 ns are achieved for fixed GPS receiver situations. Future improvements are anticipated by combining both GPS and Galileo data towards computing a timing solution.     

Manifestation of the cotton-mouton effect in the ionosphere plasma

Polarization methods used to sound ionospheric plasma are based on the Faraday and Cotton-Mouton effects. While the Faraday effect (rotation of the polarization plane) covers almost the entire ray path, the Cotton-Mouton effect gives rise to local transformation of circularly polarized waves near a point of orthogonality of the ray and the Earth's magnetic field. Comparison of the input and output polarization of probing electromagnetic waves, emitted by a satellite and received by ground stations, can provide valuable information about local plasma parameters near the orthogonality point. This paper presents a theory of interaction of circular waves near this point based on the quasi-isotropic approximation (QIA) of geometrical optics and describes algorithms that can be used to retrieve local plasma parameters from polarization measurements. Experimental configurations to observe the Cotton-Mouton effect with linearly and arbitrarily polarized receivers are discussed.     

同步卫星讯号显示的电离层闪烁特性

本文利用1983年5—8月,1984年5—12月在武昌(114.4°E,30.6°N)对日本ETS-Ⅱ卫星(130.0°E)发出的136.1124MHz讯号的观测资料进行了统计分析。结果表明:(1)武昌电离层闪烁不但有日变化,而且有季变化。每年5—7月为闪烁最大活动期,在这些月份的夜间常出现法拉弟旋转角类波扰动伴随有强闪烁现象。武昌电离层闪烁是属于中纬闪烁型;(2)闪烁指数与法拉弟旋转角起伏密切相关,它们出现率之间的相关系数为0.8以上;夜间闪烁与扩展F层,白天闪烁与突发E层出现率之间的相关系数分别为0.6和0.55。      

DEMETER卫星记录到的电离层加热现象

在法国DEMETER卫星运行期间, 地基电离层加热装置SURA和HAARP开展了一系列加热试验, 记录到各类电离层异常信息, 发现电离层加热过程中卫星观测的电离层扰动信号包括HF发射泵波及边带泵波、VLF人工源增强及频谱拓展、ULF/ELF/VLF调制波、ELF电磁扰动、ULF谐振波、等离子体特征参量扰动及高能粒子沉降等. 由于传播及耦合机制的差异, 发射泵波可以穿透电离层直达卫星高度, 其观测概率最高达到68%以上, 其他扰动受发射调制模式及当地电磁环境等影响,观测概率相对较低, 均在40%左右, 有些甚至是某次试验中出现的个别事例. 结合中国地震电磁监测试验卫星飞行轨道设计及载荷配置等,对未来开展加热试验进行了分析论证, 并参考DEMETER卫星试验结果给出了一些建议.      

1984年4月24日大太阳耀斑爆发对电离层电子总含量的影响

本文给出1984年4月24日2356UT太阳耀斑爆发期间在新乡和重庆两地利用法拉第技术接收日本同步卫星ETS-Ⅱ的甚高频信号所得到的电离层电子总含量的异常变化。两站在耀斑爆发期间的三分半钟内同时观测到电离层电子总含量的突然急剧增加。它们的增量分别为9.4×1016和14.3×1016ele/m2.本文还将偏振仪所观测到的现象与电离层垂测记录及甚低频锁相接收机所观测到的记录作了比较。分析的结果表明,大太阳耀斑期间不仅D层的电子浓度大大增加,而且F层的电子浓度也显着增加,后者是这次总含量剧增的主要部分。      

利用C频段卫星电视信号研究电离层闪烁

本文介绍卫星电视信号特性和电高层闪烁的观测结果。结果说明在民用卫星TV接收机上配接口电路接收卫星电视信号能作c频段电离层闪烁研究。      

Statistical evaluation of GLONASS amplitude scintillation over low latitudes in the Brazilian territory

The ionospheric scintillation, generated by the ionospheric plasma irregularities, affects the radio signals that pass through it. Their effects are widely studied in the literature with two different approaches. The first one deals with the use of radio signals to study and understand the morphology of this phenomenon, while the second one seeks to understand and model how much this phenomenon interferes in the radio signals and consequently in the services to which these systems work. The interest of several areas, particularly to those that are life critical, has increased using the concept of satellite multi-constellation, which consists of receiving, processing and using data from different navigation and positioning systems. Although there is a vast literature analyzing the effects of ionospheric scintillation on satellite navigation systems, the number of studies using signals received from the Russian satellite positioning system (named GLONASS) is still very rare. This work presents for the first time in the Brazilian low-latitude sector a statistical analysis of ionospheric scintillation data for all levels of magnetic activities obtained by a set of scintillation monitors that receive signals from the GLONASS system. In this study, data collected from four stations were used in the analysis; Fortaleza, Presidente Prudente, São José dos Campos and Porto Alegre. The GLONASS L-band signals were analyzed for the period from December 21, 2012 to June 20, 2016, which includes the peak of the solar cycle 24 that occurred in 2014. The main characteristics of scintillation presented in this study include: (1) the statistical evaluation of seasonal and solar activity, showing the chances that an user on similar geophysical conditions may be susceptible to the effects of ionospheric scintillation; (2) a temporal analysis based on the local time distribution of scintillation at different seasons and intensity levels; and (3) the evaluation of number of simultaneously affected channels and its effects on the dilution of precision (DOP) for GNSS users are also presented in order to alert the timetables in which navigation will be most susceptible to such effects, as well as statistics on simultaneously affected channels. Relevant results about these statistical characteristics of scintillation are presented and analyzed providing relevant information about availability of a navigation system.     

High-frequency radio experiments with the WISP system on Spacelab

WISP/HF is the medium- and high-frequency part of the Waves-In-Space-Plasmas facility. It is a flexible Shuttle/Spacelab instrument for transmitting, receiving and processing signals in the 0.3 to 30 MHz range. WISP/HF will be used to study the transmitting antenna, fundamentals of electromagnetic (EM) and electrostatic (ES) waves in magnetoplasmas, plasma instabilities and nonlinearities, and sounding of ionospheric structure.     

基于单频星载GPS数据的低轨卫星精密定轨

为满足搭载单频GPS接收机低轨卫星的精密定轨需求以及深化单频定轨研究,文中解决了单频星载GPS数据的周跳探测问题,并利用“海洋二号”（HY-2A）卫星及“资源三号”（ZY-3）卫星的单频星载GPS实测数据采用两种方法确定了二者的简化动力学轨道,并通过观测值残差分析、与双频精密轨道比较、激光测卫数据检核等方法对所得轨道精度进行评定。结果表明,在不考虑电离层延迟影响的情况下,HY-2A卫星定轨精度为2~3dm,ZY-3卫星为1m左右;而采用半和改正组合消除电离层延迟一阶项影响后,二者定轨精度均显著提高,HY-2A卫星三维精度提高至1dm左右,ZY-3卫星提高至1~2dm。文章的研究成果表明,搭载单频GPS接收机的低轨卫星也可获得厘米级的定轨精度。     

An improved approach to model regional ionosphere and accelerate convergence for precise point positioning

Given the severe effects of the ionosphere on global navigation satellite system (GNSS) signals, single-frequency (SF) precise point positioning (PPP) users can only achieve decimeter-level positioning results. Ionosphere-free combinations can eliminate the majority of ionospheric delay, but increase observation noise and slow down dual-frequency (DF) PPP convergence. In this paper, we develop a regional ionosphere modeling and rapid convergence approach to improve SF PPP (SFPPP) accuracy and accelerate DF PPP (DFPPP) convergence speed. Instead of area model, ionospheric delay is modeled for each satellite to be used as a priori correction. With the ionospheric, wide-lane uncalibrated phase delay (UPD) and residuals satellite DCBs product, the wide-lane observations for DF users change to be high-precision pseudorange observations. The validation of a continuously operating reference station (CORS) network was analyzed. The experimental results confirm that the approach considerably improves the accuracy of SFPPP. For DF users, convergence time is substantially reduced.     

New field of application of the IRI modeling – Determination of ionosphere transfer characteristic for radio astronomical signals

We suggest a new field of application of IRI modeling – determination of ionosphere transfer characteristic (ITC) for radio astronomical signals (RAS). VHF and HF RAS are widely used for observations of the Sun and pulsars. It is necessary to take into account possible distortions of RAS in the Earth ionosphere. However, in contrast to modern navigation systems (GPS, GLONASS, GALILEO), where very accurate reconstruction of ionosphere parameters is a built-in function, in present-day radio astronomy a retrieve of ITC has not been appropriately worked out yet. It collides with increasing requirements to accuracy of the analysis of RAS amplitude profile and to the angular and polarizing resolution of radio telescopes of new generation. We have developed a method and software for calculation of the ionosphere measure of rotation (RM) and the measure of dispersion (DM). We used the ionosphere model IRI-2001, magnetic-field model IGRF-10 and values of ionosphere total electron content as deduced from GPS measurements. The obtained values of the ionosphere DM and RM were recalculated into characteristics of phase delay, Faraday amplitude modulation and polarization changes. We made calculations for different levels of geomagnetic activity and for different angular position of radio sources as well.     

从射电天文观测中提取电离层信息的一种统计方法

本文在分析了法拉第旋转效应、多源观测效应和程差补偿误差等对可见度函数的相位的影响的基础上,确认了:当电离层不规则性尺度较基线长为大时,仅有电离层引起的可见度函数的相位与基线长成正比且具有随时间快变化的特点这一物理事实;从而提出了从米波综合孔径射电望远镜的观测数据中提取电离层信息的统计方法,并分析了该法的特点,给出了统计实例.      

Fading in the HF ionospheric channel and the role of irregularities

It is well known that the ionosphere affects radio wave propagation especially in the high frequency (HF) range. HF radio waves reflected by the ionosphere can reach considerable distances, often with changes in amplitude, phase, and frequency. The ionosphere is a dispersive in frequency and time, bi-refractive, absorbing medium, in which multipath propagation due to traveling irregularities is very frequent. The traveling irregularities undulate the reflecting ionospheric layer, introducing variations in signal amplitude (fading). In this multipath time variant channel fading is mainly considered, even though it is not the sole effect. Echo signals from a single reflection, as in ionospheric vertical sounding (VIS) techniques, are affected by a certain degree of variability even in quiet ionospheric conditions. In this work the behavior of the ionospheric channel is studied and characterized by observing the power variation of received echoes using the VIS technique. Multipath fading was analyzed quantifying the power variation of the signal echo due to irregularities on a temporal scale from 0.5 to 256 s. An experimental set-up derived from an ionosonde was implemented and the analysis was performed employing a special numerical algorithm operating off-line on the acquired time sequence of the signal. The gain-loss of the irregularity shapes are determined in some special cases.     

Impact of geomagnetic storm of September 7–8, 2017 on ionosphere and HF propagation: A multi-instrument study

The present study reveals the features of ionospheric parameters variations during the geomagnetic storm of September 7–8, 2017. In particular, parameters of vertical (foF2, foEs) and oblique ionospheric sounding (MOF, modes), absorption level, Total Electron Content (TEC) and particle fluxes at high altitudes were under analysis. The storm was characterized by two Dst-index mimima and can be considered as a sequence of two storms: first - with Dstmin?=??142?nT at 02 UT on September 8th and second - with Dstmin?=??122?nT and at 15 UT on September 8th. It was found that these two storms had different impacts on the ionosphere and HF propagation at mid- and high-latitudes of Northern Hemisphere. The signals of vertical and oblique ionospheric sounding were present in all ionograms before the first storm. Further, at the maximum of the first storm these signals were totally absorbed. Then, before the second storm and during its maximum the signals were detected again in the ionograms due to the low absorption. GOES satellite data showed the significant burst of electrons and protons only during the first storm and small particle fluxes - during the second storm. This feature was also confirmed with GPS data: TEC increased during the first storm and decreased during the second storm.     

Impact of heliogeophysical disturbances on ionospheric HF channels

The article presents the results of the observation of a strong magnetic storm and two X-ray flares during the summer solstice in 2015, and their impact on the HF signals characteristics in ionospheric oblique sounding. It was found that the negative phase of the magnetic storm led to a strong degradation of the ionospheric channel, ultimately causing a long blackout on paths adjacent to subauroral latitudes. On mid-latitude paths, the decrease in 1FMOF reached ～50% relative to the average values for the quiet ionosphere. It is shown that the propagation conditions via the sporadic Es layer during the magnetic storm on a subauroral path are substantially better than those for F-mode propagation via the upper ionosphere. The delay of the sharp decrease in 1FMOF during the main phase of the magnetic storm allowed us to determine the propagation velocity of the negative phase disturbances (～100 m/s) from subauroral to mid-latitude ionosphere along two paths: Lovozero – Yoshkar-Ola and Cyprus – Nizhny Novgorod. It is shown that both the LOF and the signal/noise ratio averaged over the frequency band corresponding to the propagation mode via the sporadic Es layer correlate well with the auroral AE index. Using an over-the-horizon chirp radar with a bistatic configuration on the Cyprus – Rostov-on-Don path, we located small-scale scattering irregularities responsible for abnormal signals in the region of the equatorial boundary of the auroral oval.     

Application of small-size antennas for estimation of angles of arrival of HF signals scattered by ionospheric irregularities

A modification of the Doppler Interferometry Technique is suggested to enable estimating angles of arrival of comparatively broadband HF signals scattered by random irregularities of the ionospheric plasma with the use of small-size weakly directional antennas. The technique is based on the measurements of cross-spectra phases of the probe radiation recorded at least in three spatially separated points. The developed algorithm has been used to investigate the angular and frequency-time characteristics of HF signals propagating at frequencies above the maximum usable one (MUF) for the direct radio path Moscow-Kharkiv. The received signal spectra show presence of three families of spatial components attributed, respectively, to scattering by plasma irregularities near the middle point of the radio path, ground backscatter signals and scattering of the sounding signals by the intense plasma turbulence associated with auroral activations. It has been shown that the regions responsible for the formation of the third family components are located well inside the auroral oval. The drift velocity and direction of the auroral ionosphere plasma have been determined. The obtained estimates are consistent with the classical conception of the ionospheric plasma convection at high latitudes and do not contradict the results of investigations of the auroral ionosphere dynamics using the SuperDARN network.     

基于星载AIS数据的TEC测量方法

基于星载船舶自动识别系统（AIS），提出一种计算全球电离层电子总含量（TEC）的方法。通过在卫星上搭载两个相互垂直的线极化天线，测量AIS信号穿过电离层时的法拉第旋转角，再通过法拉第旋转角与TEC的关系估算TEC。基于天拓五号卫星的AIS数据进行了实验验证，并分析了硬件设备误差和观测参数误差对结果造成的影响。实验表明，本方法测量出的TEC值与基于全球定位系统（GPS）测量的TEC值差值平均为0.762 TECU，证明了此方法的可行性。与现有的TEC测量方法相比，该方法只需利用现有的AIS系统，无需部署地面站，可大幅提高数据更新速率。      

Comparison between HF propagation and DEMETER satellite measurements within the mid-latitude trough

The morphology of the auroral, sub-auroral and mid-latitude trough region of the ionosphere is strongly dependent on the interplanetary magnetic field and the level of geomagnetic activity. Changes in the morphology impact on the characteristics of HF signals propagating through these regions of the ionosphere. In order to develop a better understanding of these effects, a number of experiments have recently been undertaken in which the time of flight and direction of arrival of HF signals have been measured over several paths aligned along the mid-latitude trough. In addition, observations made by the DEMETER satellite of the mid-latitude trough electron density structure, dynamics and wave activity were used in order to investigate the effect of the fine structure of the ionosphere on HF signals. For two types of relatively common night time HF time of flight and azimuth of arrival behaviour (referred to here and elsewhere as ‘Type 1’ and ‘Type 2’ propagation), the signal behaviour is consistent with scatter from irregularities in the auroral region in the one case, and from irregularities present on the floor of the trough in the other.     

VHF/UHF振幅闪烁和VHF快速法拉弟旋转起伏

本文利用1988年9月至1989年5月在武昌(114.4°E,30.6°N)同时接收日本ETS-Ⅱ卫星(130.0°E)发出的VHF(136MHz)信标信号和苏联静止站-T卫星(99.0°E)发出的UHP(714MHz)广播电视信号时获得的观测记录,对夜间出现的双频(VHF/UHF)闪烁和VHF快速(每分钟大于5次的起伏)法拉弟旋转起伏(以下用FRF表示法拉弟旋转起伏)进行了统计分析,结果发现在临近太阳黑子最大年份观测到的双频夜间闪烁主要为急始型,呈赤道特性,且在临近二分点的月份里有最大出现率,秋季更为明显;伴随VHF振幅闪烁出现的快速FRF常与UHF振幅闪烁共存,以及产生这种现象的不规则体由西向东漂移,东-西向的漂移速度分量,在子夜前为140m/s,在子夜后为90m/s。