大耀斑期间向日面电离层总电子含量的响应个例分析

利用2001年4月15日1336UT耀斑爆发期间向日面GPS观测数据提取的总电子含量的时间变化曲线。分析了向日面电离层对这次耀斑的响应特点．结果表明，耀斑期间向日面电离层出现了总电子含量突增事件．最大总电子含量增加量约为2．6TECU，在0600LT和1800LT都观测到了总电子含量突增，世增加幅度仅为0．5-1TECU．在高纬地区，由于电离层闪烁，从TEC时间变化曲线提取不出来总电子含量增加值．从各卫星星下点处的TEC增加量和各星下点处的太阳天顶角的关系可以看到，TEC增加量与太阳天顶角有关，太阳天顶角越大，TEC增幅越小。另外，从总电子含量时间变化率曲线上还观测到了时间同步的小尺度扰动，通过与耀斑期间硬X射线辐射通量的比较，发现两者有明显的相关性，电离层中的这种扰动与耀斑期间的硬X射线或远紫外辐射有关．     

太阳活动对电离层TEC变化影响分析ormalsize

为研究太阳活动对电离层TEC变化的影响,从整体到局部分析了2000—2016年的太阳黑子数、太阳射电流量F_10.7指数日均值与电离层TEC的关系,并重点分析了2017年9月6日太阳爆发X9.3级特大耀斑前后15天太阳活动与电离层TEC变化的相关性.结果表明:由2000—2016年的数据整体看来,太阳黑子数、太阳F_10.7指数、TEC两两之间具有很强的整体相关性,但局部相关性强弱不均;此次耀斑爆发前后太阳黑子数、太阳F_10.7指数和TEC具有很强的正相关特性,太阳活动对TEC的影响时延约为2天;太阳活动对全球电离层TEC的影响不同步,从高纬至低纬约有1天的延迟,且对低纬度的影响远大于中高纬度.太阳活动是影响电离层TEC变化的主要原因,但局部也可能存在其他重要影响因素.      

太阳耀斑对电离层总电子含量的影响

本文分析了1978—1979年1级以上的太阳耀斑对电离层总电子含量的影响. 给出了不同持续时间、不同亮度、不同季节、发生在日面不同位置上的太阳耀斑对电离层总电子含量的影响.分析结果表明,持续时间大于等于1.5小时的耀斑对电子含量有明显的扰动,耀斑出现后电子含量随之增加,在第4—5天增加到最大值,扰动持续数日;持续时间小于1.5小时的耀斑对电子含量影响甚微;非亮耀斑对电子含量的扰动小于亮耀斑;夏季出现的耀斑对电子含量无明显扰动,只有冬季出现的亮耀斑对电子含量有明显的扰动;太阳耀斑扰动电子含量有明显的日面位置东西不对称性,只有出现在日面东边、特别是E₃区的太阳耀斑对电子含量才有明显的扰动.      

太阳活动对电离层TEC变化影响分析

为研究太阳活动对电离层TEC变化的影响,从整体到局部分析了2000-2016年的太阳黑子数、太阳射电流量F_(10.7)指数日均值与电离层TEC的关系,并重点分析了2017年9月6日太阳爆发X9.3级特大耀斑前后15天太阳活动与电离层TEC变化的相关性.结果表明:由2000-2016年的数据整体看来,太阳黑子数、太阳F_(10.7)指数、TEC两两之间具有很强的整体相关性,但局部相关性强弱不均;此次耀斑爆发前后太阳黑子数、太阳F_(10.7)指数和TEC具有很强的正相关特性,太阳活动对TEC的影响时延约为2天;太阳活动对全球电离层TEC的影响不同步,从高纬至低纬约有1天的延迟,且对低纬度的影响远大于中高纬度.太阳活动是影响电离层TEC变化的主要原因,但局部也可能存在其他重要影响因素.     

日面耀斑环中物质的运动

利用云南天文台1980年7月14日3B级双带耀斑的光学观测资料,以及SMM卫星对同一耀斑的X射线观测结果,讨论日面耀斑环中物质的运动规律。先比较耀斑Hα象和X射线象的日面位置,根据投影效应确定耀斑环的高度;然后从理论上估算由于耀斑环中物质下落,所形成的耀斑活动区视向速度的分布。所得结果与观测资料基本相符。      

2009年6至7月华南地区电离层TEC扰动研究

电离层TEC（Total Electron Content）扰动与多种扰动源相关联．2009年6至7月期间存在地震和日全食的扰动源．利用广州地区GPS监测网在2009年6至7月连续监测到的TEC数据,通过采用前15天数据的滑动窗口对数据进行处理,从时间序列和空间分布两方面分析了华南地区电离层TEC扰动特征．结果显示,2009年6至7月华南地区电离层TEC扰动和该时期发生的地震以及日全食事件可能有关联;2009年7月多个地震发生引起的电离层扰动特征为,震前出现的是正异常,发震当天或震后有可能是正异常,也有可能是负异常;7月22日日全食当天TEC扰动为正异常,推测该正异常是地磁活动、地震活动及日全食综合效应的结果．     

利用MF雷达对耀斑期间电离层D区电子密度的观测研究

利用MF雷达观测资料对X级别耀斑爆发期间在66-80km高度之间的电子密度进行了研究，观测到了耀斑爆发期间电子密度的突然增加，在较低高度上的电子密度的时间变化趋势与耀斑的软X射线辐射通量相关．电子密度的变化强度依赖于具体的耀斑参数，有些耀斑引起的电子密度增加高达400cm^-3，有些仅为100cm^-3左右．但耀斑期间在这一高度区间增加的总电子含量增量仅占耀斑辐射引起的整个电离层总电子含量增量的千分之一左右．最后，利用恢复阶段电子密度的时间变化过程估算了1997年11月4日耀斑期间部分高度上的有效复合系数．     

磁暴期间电离层扰动的GPS台网观测分析

给出了一种利用GPS台网观测获取TEC快速变化的计算方法，并将该方法用于东亚一澳大利亚扇区的GPS台网观测数据，分析了2000年7月14—18H大磁暴期间的电离层响应，揭示出电离层暴期间赤道异常峰的压缩和移动等特性．计算结果表明，在站点分布不均匀、原始观测数据不足且随时间跳变等多种不利因素的影响下，这种新的算法仍能保持很好的计算稳定性，并能快速地提取给定时空范围内的三维TEC短时变化的特征，适用于研究电离层暴等情况下引起的TEC扰动．     

太阳耀斑和地磁扰动的统计分析(1966—1978)

本文给出了不同等级、不同持续时间、发生在日面不同日心经距上的太阳耀斑所引起的各种地磁指数(Ap、AE、Dst和Kp指数)的变化,讨论了各类耀斑所引起的地磁扰动的特点以及耀斑的日心经距及其喷发物在日地空间的传播速度对磁扰强度的影响。      

2000年7月和2003年10月大磁暴期间东亚地区中低纬电离层的GPS TEC的响应研究

利用武汉电离层观象台研制的GPS TEC的现报方法及现报系统,对东亚地区GPS台网的观测数据进行处理分析,特别对2000年7月14-18日和2003年10月28日至11月1日两次特大磁暴期间的数据进行了对比考察,文中分析了两次磁暴间的电离层响应,得到对应不同磁暴时段电离层TEC的不同变化情况,着重揭示了TEC赤道异常峰的压缩和移动以及赤道异常随时间的压缩—反弹—恢复的过程,并结合高纬电离层的部分响应机制进行了说明,结果显示,两次磁暴期的电离层响应表现出了各自不同的特点,从而反映出因季节变化引起的高纬电离层暴时能量注入的不同而造成的全球性电离层扰动的不同形态,由此看出,磁暴期间电离层TEC的变化直接与太阳扰动发生的时间及其对高纬电离层的耦合有关,若短时期内连续发生多次磁暴,则电离层反应更加复杂,不能简单地当做单一磁暴叠加处理。     

Day-to-day variability of equatorial anomaly in GPS-TEC during low solar activity period

The ionospheric total electron content (TEC) in the northern hemispheric equatorial ionization anomaly (EIA) crest region is investigated by using dual-frequency signals of the Global Positioning System (GPS) acquired from Rajkot (Geog. Lat. 22.29°N, Geog. Long. 70.74°E; Geom. Lat. 14.21°N, Geom. Long. 144.90°E), India. The day-to-day variability of EIA characteristics is examined during low solar activity period (F10.7∼83 sfu). It is found that the daily maximum TEC at EIA crest exhibits a day-to-day and strong semi-annual variability. The seasonal anomaly and equinoctial asymmetry in TEC at EIA is found non-existent and weaker, respectively. We found a moderate and positive correlation of daily magnitude of crest, Ic with daily F10.7 and EUV fluxes with a correlation coefficient of 0.43 and 0.33, respectively indicating an existence of a short-term relation between TEC at EIA and the solar radiation even during low solar activity period. The correlation of daily Ic with Dst index is also moderate (r = −0.35), whereas no correlation is found with the daily Kp index (r = 0.14) respectively. We found that the magnitude of EIA crest is moderately correlated with solar flux in all seasons except winter where it is weakly related (0.27). The magnitude of EIA crest is also found highly related with EEJ strength in spring (r = 0.69) and summer (r = 0.65) than autumn (0.5) and winter (r = 0.47), though EEJ is stronger in autumn than spring.     

流星突发通信信道日变化预测模型

流星突发通信不同于传统的通信, 其是低速率通信, 具有突发、不连续、不定时的特性. 因此, 流星余迹通信的复杂性要求有必要对其通信信道进行建模. 在流星通信链路中, 流星的辐射分布、可用流星率和占空比是影响流星通信信道性能的重要参数. 流星辐射分布在不同季节不同时间都各不相同, 因此准确预测流星通信链路在不同时间的流星辐射分布, 从而改变大圆路径上天线的指向, 对提高通信速率显得非常重要. 同时, 准确预测流星突发通信链路上的可用流星率和占空比, 有助于准确预测并建立流星突发信道模型. 本文分析研究了偶发流星辐射分布建模的发展, 建立了偶发流星日心空间和地心空间的几何关系, 得到了流星突发通信信道参数预测模型. 并将预测模型应用于流星通信链路, 预测结果与通信链路观测结果比较一致, 为流星通信系统的建立提供了技术支持.      

A study on Nighttime Winter Anomaly (NWA) and other related Mid-latitude Summer Nighttime Anomaly (MSNA) in the light of International Reference Ionosphere (IRI) – Model

The ionospheric Nighttime Winter Anomaly (NWA) is a feature observed in the Northern Hemisphere at the American and in the Southern Hemisphere at the Asian longitude sector under low solar activity conditions. Jakowski et al. (2015) analyzed ground-based GPS derived TEC and peak electron density data from radio occultation measurements on Formosat-3/COSMIC satellites and confirmed the persistence of the phenomenon. Further, they assumed that Mid-latitude Summer Nighttime Anomaly (MSNA) and related special anomalies such as the Weddell Sea Anomaly (WSA) and the Okhotsk Sea Anomaly (OSA) are closely related to the NWA via enhanced wind-induced uplifting of the ionosphere. The aim of this paper is to study the factors causing these anomalies and also to investigate if these anomalies are re-produced by IRI. The results show that IRI model does include the NWA effect, though at a different longitude and could be improved for better predictions. The IRI-2016 model does show WSA in TEC but not in NmF2. Further, the IRI-2016 model could clearly predict the OSA both in NmF2 and TEC.     

动力系统的Lyapunov稳定性和吸引性

对度量空间中动力系统的Ｌｙａｐｕｎｏｖ稳定性与吸引性之间的关系进行了研究，证明了连通局部紧空间中吸引子和全局吸引子是等价的     

Accuracy analysis of GNSS-IR snow depth inversion algorithms

In recent years, with the continuous development of Global Navigation Satellite System (GNSS), it has been applied not only to navigation and positioning, but also to Earth surface environment monitoring. At present, when performing GNSS-IR (GNSS Interferometric Reflectometry) snow depth inversion, Lomb-Scargle Periodogram (LSP) spectrum analysis is mainly used to calculate the vertical height from the antenna phase center to the reflection surface. However, it has the problem of low identification of power spectrum analysis, which may lead to frequency leakage. Therefore, Fast Fourier Transform (FFT) spectrum analysis and Nonlinear Least Square Fitting (NLSF) are introduced to calculate the vertical height in this paper. The GNSS-IR snow depth inversion experiment is carried out by using the observation data of P351 station in PBO (Plate Boundary Observatory) network of the United States from 2013 to 2016. Three algorithms are used to invert the snow depth and compared with the actual snow depth provided by the station 490 in the SNOTEL network. The observations data of L1 and L2 bands are respectively used to find the optimal combination between different algorithms further to improve the accuracy of GNSS-IR snow depth inversion. For L1 band, different snow depths correspond to different optimal algorithms. When the snow depth is less than 0.8 m, the inversion accuracy of NLSF algorithm is the highest. When the snow depth is greater than 0.8 m, the inversion accuracy of FFT algorithm is higher. Therefore, according to the different snow depth, a combined algorithm of NLSF + FFT is proposed for GNSS-IR snow depth inversion. Compared with the traditional LSP algorithm, the inversion accuracy of the combined algorithm is improved by 10%. For L2 band data, the results show that the accuracy of snow depth inversion of various algorithms do not change with the variations of snow depth. Among the three single algorithms, the inversion accuracy of FFT algorithm is better than that of LSP and NLSF algorithms.     

Effect of biases in integrity monitoring for RTK positioning

In road transport, continuous high-accuracy positioning is required in real time. To ensure the proper functioning and safety of vehicular applications, integrity monitoring (IM) is needed to protect from the positioning errors under a certain alert limit (AL) with a pre-defined probability of misleading information (MI). In this study, a detailed threat model is developed for real-time kinematic (RTK) positioning application of short baselines. The model distinguishes between ambiguity-float and -fixed scenarios, and considers the influences of phase and code multipath as well as between-receiver atmospheric residuals. With the float ambiguities temporally constrained, the bias contribution that propagates with time-updated ambiguities was studied analytically for the horizontal protection level (HPL) in IM. Based on real data from both static and kinematic experiments, HPL was computed along the direction of the semi-major axis of the horizontal error ellipse. In ambiguity-float and -fixed cases, the HPL was mostly several meters and decimetres, respectively. It was found that time-propagated biases play a dominant role in the ambiguity-float HPL, and among them, phase and code multipath had in general the largest contributions. For ambiguity-fixed case, the phase multipath was found to play a dominant role in the HPL. This shows the importance of considering the biases in the RTK IM for both the ambiguity-float and -fixed scenarios. Given a horizontal alert limit (HAL) of 5 m, the availabilities of ambiguity-float solutions were low, i.e., below 50% for the static roof tests and below 5% for the kinematic road tests. For the ambiguity-fixed scenario, with HAL at 0.5 m, integrity availability was nearly 100% for the static roof tests and above 85% for the kinematic road tests.     

基于DSP的飞机全电刹车模糊神经网络控制系统

介绍了一种基于DSP的飞机全电刹车模糊神经网络控制系统 ,此系统以电作动器取代液压机构。由于不使用液压机构使得系统更加安全 ,同时刹车效率也有所提高。仿真及试验结果显示该系统具有良好的性能 ,达到了设计要求。     

Variation of ionospheric total electron content in Indian low latitude region of the equatorial anomaly during May 2007–April 2008

The ionospheric total electron content (TEC), derived by analyzing dual frequency signals from the Global Positioning System (GPS) recorded near the Indian equatorial anomaly region, Varanasi (geomagnetic latitude 14°, 55′N, geomagnetic longitude 154°E) is studied. Specifically, we studied monthly, seasonal and annual variations as well as solar and geomagnetic effects on the equatorial ionospheric anomaly (EIA) during the solar minimum period from May 2007 to April 2008. It is found that the daily maximum TEC near equatorial anomaly crest yield their maximum values during the equinox months and their minimum values during the summer. Using monthly averaged peak magnitude of TEC, a clear semiannual variation is seen with two maxima occurring in both spring and autumn. Statistical studies indicate that the variation of EIA crest in TEC is poorly correlated with Dst-index (r = −0.03) but correlated well with Kp-index (r = 0.82). The EIA crest in TEC is found to be more developed around 12:30 LT.     

Orbit determination for the GOCE satellite

Precise Orbit Determination (POD) for the Gravity field and steady-state Ocean Circulation Explorer (GOCE), the first core explorer mission by the European Space Agency (ESA), forms an integrated part of the so-called High-Level Processing Facility (HPF). Two POD chains have been set up referred to as quick-look Rapid and Precise Science Orbit determination or RSO and PSO, respectively. These chains make use of different software systems and have latencies of 1 day and 2 weeks, respectively, after tracking data availability. The RSO and PSO solutions have to meet a 3-dimensional (3D) position precision requirement of 50 cm and a few cm, respectively. The tracking data will be collected by the new Lagrange GPS receiver and the predicted characteristics of this receiver have been taken into account during the implementation phase of the two chains.     

粒子群优化粒子滤波的接收机自主完好性监测

接收机自主完好性监测（RAIM）是航空卫星导航接收机必不可少的功能,为保持全球卫星导航系统（GNSS）在卫星发生故障时系统性能不降级,需要对卫星故障进行检测和隔离。针对接收机观测噪声非高斯分布的特点,提出一种基于粒子群优化粒子滤波（PSO-PF）的故障检测和隔离算法。通过粒子群优化粒子滤波对状态估计进行一致性检验实现故障检测。采集实测数据验证算法的检测性能,并与基于基本粒子滤波的完好性监测算法进行比较,结果表明:本文所提算法在非高斯测量噪声下可检测并隔离全球定位系统（GPS）故障卫星,其性能优于基于基本粒子滤波的完好性监测算法性能,对研究北斗卫星导航系统（BDS）接收机自主完好性监测具有一定的意义。