Behavior of the equivalent slab thickness over three European stations

The total electron content (TEC) derived from the global positioning system (GPS) and the F2-layer peak electron density obtained from Digisonde data have been used to study the diurnal, seasonal and solar activity variations of the ionospheric equivalent slab thickness (τ) over three European stations located at Pruhonice (50.0°N, 15.0°E), Ebro (40.8°N, 0.5°E) and El Arenosillo (37.1°N, 353.3°E). The diurnal variation of the τ is characterized by daytime values lower than nighttime ones for all seasons at low solar activity while daytime values larger than nighttime characterizes the diurnal variation for summer at high solar activity. A double peak is noticeable at dusk and at dawn, better expressed for winter at low solar activity. The seasonal variations of τ depend on local time and solar activity, the daytime values of τ increases from winter to summer whereas nighttime values of τ show the opposite. The effect of the solar activity on τ depends on local time and season, there being very sensitive for winter nighttime values of τ. The results of this study are compared with those presented by other authors.     

Comparative analysis of TEC disturbances over tropical cyclone zones in the North–West Pacific Ocean

In this paper, we study ionospheric total electron content (TEC) disturbances associated with tropical cyclones (TCs). The study relies on the statistical analysis of six cyclones of different intensity which occurred in the North–West Pacific Ocean in September–November 2005. We have used TEC data from the international network of two-frequency ground-based GPS receivers and NCEP/NCAR meteorological archive. TEC variations of different period ranges (02–20 and 20–60 min) are shown to be more intense during TC peaks under quiet geomagnetic conditions. The highest TEC variation amplitudes are registered when the wind speed in the cyclone and the TC area are maximum. The intensification of TEC disturbances is more pronounced when several cyclones occur simultaneously. We have revealed that the ionospheric response to TC can be observed only after the cyclone has reached typhoon intensity. The ionospheric response is more pronounced at low satellite elevation angles.     

空运油料容器地面模拟试验技术研究

空运油料容器地面模拟试验是验证飞机空运油料容器在正常飞行状态、紧急着陆时油料容器的结构强度是否满足设计要求的重要手段之一。针对试验中的碰撞波形控制技术、试验误差要求、软体油料容器的重心变化量等关键技术进行了探讨,为油料容器模拟试验方面的研究工作提供参考。     

WAAS电离层延迟网格校正中的用户算法研究

从广域增强系统WAAS中对电离层延迟的网格校正算法出发,分析了用户基于网格校正的电离层校正算法,阐明了核算法的原理并详细推导了计算公式和计算过程.     

地磁活动对电离层f0F2月中值的影响与国际参考电离层误差

利用我国9个中低纬度的电离层观测站在1977-1986年间观测的f0F2月中值,按每月的平均地磁活动指数Ap分为地磁活动高（Ap≥5）和低（Ap＜15）两种情况,研究了地磁活动对f0F2月中值平均低纬电离层驼峰区演变的影响,并考察了国际参考电离层（IRI）的误差．     

基于偏差模型的导弹发射动力学仿真

基于偏差模型的导弹发射动力学仿真是根据偏差来源建立相应的偏差模型,将偏差力、力矩与标准状态下的受力叠加得到导弹实际受力,再进行运动状态的求解.这种基于偏差模型的仿真系统既能够单独分析各项干扰因素对发射精度的影响,还能够综合多项干扰进行数值打靶模拟分析.针对某舰载倾斜发射导弹,仿真分析了发射臂振动、推力偏心、导轨不平、舰船运动等干扰因素对初始扰动的影响,并进行了5 000次数值打靶统计分析.在给定的干扰概率分布条件下,命中概率达到93.86%.     

基于时频域增强和全变差的群目标信号分离

针对低分辨雷达获取的群目标信号的弱时频正交性以及难以分离的问题,在进行时频域增强处理的基础上,提出了一种基于全变差(TV)的群目标信号分离方法。在旋转目标模型的基础上,首先通过分析群目标信号的稀疏性,指出了进行时频域增强处理的必要性。然后利用群目标中各子目标对应的微动周期的差异性,通过双向延迟处理,对多次观测得到的群目标信号进行时频域增强处理。最后根据群目标信号能量区域的分布特性,利用局部TV融合和主分量分析相结合的方法,实现了群目标信号的高保真分离。仿真结果表明,在采样率较低的情况下,文中方法有效地解决了群目标信号中弱信号分量的分离及提取问题,其融合分辨效果明显优于基于TV范数的融合方法。      

Multi-station observation of ionospheric irregularities over South Africa during strong geomagnetic storms

This paper presents results pertaining to the response of the mid-latitude ionosphere to strong geomagnetic storms that occurred from 31 March to 02 April 2001 and 07–09 September 2002. The results are based on (i) Global Positioning Systems (GPSs) derived total electron content (TEC) variations accompanying the storm, (ii) ionosonde measurements of the ionospheric electrodynamic response towards the storms and (iii) effect of storm induced travelling ionospheric disturbances (TIDs) on GPS derived TEC. Ionospheric data comprising of ionospheric TEC obtained from GPS measurements, ionograms, solar wind data obtained from Advanced Composition Explorer (ACE) and magnetic data from ground based magnetometers were used in this study. Storm induced features in vertical TEC (VTEC) have been obtained and compared with the mean VTEC of quiet days. The response of the mid-latitude ionosphere during the two storm periods examined may be characterised in terms of increased or decreased level of VTEC, wave-like structures in VTEC perturbation and sudden enhancement in hmF2 and h′F. The study reveals both positive and negative ionospheric storm effects on the ionosphere over South Africa during the two strong storm conditions. These ionospheric features have been mainly attributed to the travelling ionospheric disturbances (TIDs) as the driving mechanism for the irregularities causing the perturbations observed. TEC perturbations due to the irregularities encountered by the satellites were observed on satellites with pseudo random numbers (PRNs) 15, 17, 18 and 23 between 17:00 and 23:00 UT on 07 September 2002.     

A study of L band scintillations during the initial phase of rising solar activity at an Indian low latitude station

The ionospheric scintillation and TEC (Total Electron Content) variations are studied using GPS (Global Positioning System) measurements at an Indian low latitude station Surat (21.16°N, 72.78°E; Geomagnetic: 12.90°N, 147.35°E), situated near the northern crest of the equatorial anomaly region. The results are presented for data collected during the initial phase of current rising solar activity (low to moderate solar activity) period between January 2009 and December 2011. The results show that within a total number of 656 night-time scintillation events, 340 events are observed with TEC depletions, Rate of change of TEC (ROT) fluctuations and enhancement of Rate of change of TEC Index (ROTI). A comparison of night-time scintillation events from the considered period reveal strong correlation amongst the duration of scintillation activity in S₄ index_, TEC depletion, ROT fluctuations and ROTI enhancement in the year 2011, followed by the year 2010 and least in 2009. The statistical analyses of scintillation activity with enhancement of ROTI also show that about 70–96% scintillation activity took place in equinox and winter months. Moreover, from a nocturnal variation in occurrence of scintillation with (S₄ ? 0.2) and enhancement of ROTI with (ROTI ? 0.5), a general trend of higher occurrence in pre-midnight hours of equinox and winter seasons is observed in both indices during the year 2011 and 2010, while no significant trend is observed in the year 2009. The results suggest the presence of F-region ionospheric irregularities with scale sizes of few kilometers and few hundred meters over Surat and are found to be influenced by solar and magnetic activity.     

In situ measurements of ionospheric plasma turbulence over five frequency decades: Heritage flight of the Plasma Local Anomalous Noise Experiment (PLANE)

Observations of ionospheric plasma density and frequency-dependent broadband plasma turbulence made during the heritage flight of the Plasma Local Anomalous Noise Experiment (PLANE) are presented. Rather than record high frequency time series data, the experiment was designed to record Power Spectral Distributions (PSDs) in five decadal frequency bins with upper limits ranging from 1.0 Hz to 10 kHz. Additionally, PLANE was designed distinguish turbulence in the ambient plasma from that local to the spacecraft. The instrument consists of two retarding potential analyzers (RPAs) connected together via a feedback loop to force one analyzer into the I–V trace retardation region at all times. Fluctuations in this measurement are believed to be ambient only as the RPA’s voltage would be too high for locally turbulent plasma to surmount the potential barrier, which is nominally at ram energy. The instrument requires pointing along the spacecraft’s ram velocity vector to make this measurement, thus requiring stabilization in pitch and yaw. During PLANE’s heritage flight, though the satellite’s attitude control system failed early in the mission, plasma data were collected during opportune times in which the instrument rotated into and out of the ram. Observations of plasma density and PSDs of high frequency plasma turbulence were recorded on several occasions. Additionally, a plasma source onboard the satellite was used to generate artificial plasma turbulence, and the PLANE data observed periodic structure presumably associated with the rotation of the spacecraft during these source firings. A brief comparison with other high frequency in situ plasma instruments is presented.