CAS-DIS数字电离层测高仪系统研制

提出了将射频直接采样数字化的接收方式应用于数字电离层测高仪系统的设计方案, 并详细介绍了该方案在CAS-DIS (Chinese Academy of Sciences, Digital Ionosonde)电离层测高仪系统的应用, 给出了CAS-DIS电离层测高仪在中国武汉电离层探测标校试验场和武汉-北京斜向电离层探测系统中的实验结果. 观测结果表明, 采用本文提出的数字化方案设计的电离层测高仪系统性能优越, 且可以分别工作在垂直和斜向探测模式, 满足了电离层探测的多种应用需求.      

电离层数字测高仪被动接收观测模式研究

利用CADI(Canadian Advanced Digital Ionosonde)电离层数字测高仪平台,实现了新的电离层数字测高仪被动接收观测模式.利用新开发的观测模式,在观测台站开展了一系列实验观测研究,经过信号处理和信息提取,获得了电离层特征参量f0F2回归方程,高频信道背景噪声分布,电离层D层对电波的吸收等电离层探测信息.实验观测结果表明,所获取的f0F2与主动探测结果相关性在0.84以上,高频信道背景噪声分布以及电离层D层吸收状况与电离层实际分析结果相吻合.     

敏捷数字电离层测高仪系统研制及初步观测

在小型天线和低发射功率条件下，保证电离层测高仪观测数据质量和提高观测速度一直是电离层垂测的技术难点.针对这一问题，基于新近发展的高速数字芯片和射频器件，采用窄带跟踪滤波、脉冲压缩、编码复用和天线均衡匹配等技术，设计和研制一种敏捷数字电离层测高仪.该系统采用数米高的小型收发天线和便携式主机系统，配置任意频率扫描方式频高图、高分辨率多普勒频高图和斜向探测等多种工作模式，具有可流动观测布站、系统参数灵活捷变及适合快速电离层扰动探测等能力.敏捷数字电离层测高仪为组网观测获得大范围电离层时空变化和电离层快速扰动及传播提供了一种有效的探测手段.      

风云三号C星GNOS北斗掩星电离层探测初步结果

利用风云三号卫星C星GNOS掩星探测仪电离层数据,分析了2013年10月FY-3C GNOS探测的北斗掩星电离层廓线分布,将2013年10月1日至2015年10月10日期间FY-3C GNOS观测的F₂层峰值电子密度（N_mF₂）与地面电离层测高仪观测结果进行对比,验证了FY-3C GNOS北斗电离层掩星的探测精度.结果表明,FY3-C GNOS北斗电离层掩星与电离层测高仪探测的N_mF₂数据相关系数为0.96,平均偏差为10.21%,标准差为19.61%.在不同情况下其数据精度有如下特征:白天精度高于夜晚;夏季精度高于分季,分季精度高于冬季;中纬地区精度高于低纬地区,低纬地区精度高于高纬地区; BDS倾斜同步轨道（IGSO）卫星精度高于同步轨道（GEO）卫星和中轨道（MEO）卫星.FY-3C GNOS北斗电离层掩星与国际上其他掩星电离层数据精度的一致性对GNSS掩星探测资料的综合利用具有重大意义.      

满州里上空电离层之平均特性及暴时特性

本文对1983年满州里(磁纬38.07°)的测高仪资料和子午仪卫星资料进行了处理.前者主要是对F₂层临界频率f₀F₂,而后者是对微分多普勒的总含量N_T进行分析.得到满州里上空电离层之平均特性,以及磁暴期间电离层的一些异常变化.结果发现,满州里电离层的平均特性具有典型的季节异常,且f₀F₂和N_T的变化呈现较好的一致性.满州里上空电离层的扰动大都发生在两分点季和冬季,且正相大多发生在冬季,双相大多发生在两分点季,负相大多发生在夏季和两分点季.得出1983年满州里暴时N_T和f₀F₂相对于月中值偏移量的均方根值δN_T和δf₀F₂都与磁Ap指数均方根值δAp之间存在一元线性相关.      

电离层虚高的高精度测量与分析

为了提高电离层虚高测量精度,介绍了利用电离层回波相位实现高精度虚高测量的方法,并以CADI(Canadian Advanced Digital Ionosonde)电离层数字测高仪为研究平台,进行组合脉冲控制和回波相位测量分析,开展了一系列虚高测量实验,并与传统的利用回波时间延迟的虚高测量方法进行了分析比较.实验结果表明,基于回波相位的测量分析方法与回波时延测量分析方法相比,其虚高测量精度高一个量级以上,这对精确反演电离层峰下电子浓度剖面及研究电离层精细结构具有重要意义.      

高精度多普勒频高图的获取和分析

电离层高频反射回波的多普勒频移是研究电离层扰动的一个重要参数。在数字测高仪探测中，高分辩率的多普勒频移一般在漂移测量中获得，但这种测量方式探测的频点少，不能获得扰动的高度剖面；而在频高图模式下，虽然工作的频点多，能够获得电子浓度的高度剖面的信息，但探测的多普勒频移的分辩率低，无法用来精确检测电离层扰动。实际的电离层高频回波一般为窄带信号，由此本文中提出了一种新的分析方法，利用DGS-256数字测高仪频高图模式下记录的16个多普勒通道的数据，通过反傅里叶变换还原成时域信号，采用最小二乘法估计相邻时间点的相位差，获得高精度多普勒频高图。作为实例，利用该方法分析武汉电离层观象台数字测高仪观测站的观测数据，得到了多频点的多普勒频移曲线。结果表明：在DGS-256数字测高仪频高图模式下能够得到高精度多普勒频高图，这在电离层扰动探测和研究中很在意义。     

由高频无线电波反射回波参数反演电离层运动和结构的高度剖面

本文从广义电波射线微分方程组出发,导出了时变、不均匀和各向异性电离层介质中高频无线电波反射回波的可测参数与电离层的运动和结构参数之间的积分方程组,并给出了利用现代数字测高仪中的多普勒图、定向图、频高图和测距图,反演电离层的结构和运动随高度的分布剖面的计算方法.根据这种反演方法,单站探测电离层运动和结构剖面时有多种可测参量的组合方式.文中提出了一种最佳的参量组合方案,为探测设备的改进和观测记录的分析提供了理论依据.      

利用F区电离层特性参量获取等效中性风的方法及讨论

讨论利用电离层特性参量获取F层峰值高度附近中性风信息的三类方法.这些方法主要有:传统的和改进的伺服理论方法、借助电离层模式和数据同化思想的方法和刘立波等提出的方法.并以美国Millstone Hill非相干散射雷达浓度剖面和离子速度数据,以及澳大利亚Beveridge(37°S,144°E)FPI风场和测高仪数据为个例,初步考察利用电离层特性数据导出的等效中性风与观测值的一致性.     

一种数字电离层测高仪系统中O波与X波的分离方法

电离层测高仪系统中,O波与X波的分离非常重要.本文提出一种新的O波与X波分离的实现方法,根据电离层回波的极化特性,通过在接收电路上采用数字方法合成圆极化波的方式,实现了对O波与X波的有效分离.与现有DPS-4测高仪系统采用模拟域电信号合成圆极化波的方法相比,本文方法通过在数字下变频处理过程中引入±90°相移,消除了在模拟域电信号合成方法中相移器的带宽限制和非线性问题.另外,该方法在实现发射和接收信号的极化状态转换时不需要连续切换多个模拟开关,从而提高了整个系统的稳定性.      

基于IGS电离层TEC格网的扰动特征统计分析

电离层总电子含量（TEC）是研究空间天气特性的重要参量,通过分析电离层TEC,可以了解空间环境的变化特征.利用IGS提供的1999—2016年全球电离层TEC格网数据,按照地磁纬度将全球划分为高、中、中低、低磁纬四个区域,计算不同区域的电离层扰动;利用大量统计数据选取电离层扰动事件的判定阈值,分析电离层扰动与太阳活动、时空之间的关系;计算电离层扰动指数与地磁活动之间的相关系数.结果显示:电离层扰动与太阳活动变化具有较强的正相关特性.在太阳活动低年,电离层扰动事件发生的概率约为1.79%,在太阳活动高年发生扰动的概率约为10.18%.在空间分布上,无论是太阳活动高年还是低年,高磁纬地区发生扰动事件的概率均大于其他磁纬出现扰动事件的概率.计算得到的中磁纬和中低磁纬地区电离层扰动指数与全球地磁指数Ap的相关系数分别为0.57和0.56,说明电离层扰动指数与Ap具有较好的相关关系;高磁纬电离层扰动指数与Ap的相关系数为0.44;低磁纬扰动指数与Ap的相关系数为0.39.以上结果表明,不同区域电离层扰动与全球地磁指数Ap的相关性不同,测定区域地磁指数可能会提高与电离层扰动的相关性.      

磁纬10°以下哨声路径纬度和所需抬升因子积分中值的估算方法

本文采用国际地磁参考场(1980IGRF,n=8)磁力线经验公式和三层模式电离层,结合哨声波沿磁力线传播所需电子浓度的横向梯度,给出了磁纬10°以下哨声路径纬度和所需抬升因子积分中值的估算方法;从而得出:(1)哨声色散值D不仅与电离层N_mF2正相关,而且与h_mF2也有明显相关性.当路径纬度ф₉₀≤10.5°(IGRF,n=8,下同)时,D与h_mF2负相关;>12时,正相关;在10.5°—12°之间时,正或负相关取决于路径顶点高度与h_m之差值.估算表明,三亚(磁纬7.04°N)收到的哨声中路径纬度ф₉₀≤10.5。的占94.5%,D与h_mF2负相关,这与观测结果一致.(2)所需抬升因子积分中值一般在7—31%之间.      

Models for horizontal E- and F-region drifts

Plasma transport is very important for understanding the space-time variations of the ionosphere. Therefore, following a resolution of URSI Subcommission G4, an effort is made to create a computer code describing the main results of investigations the ionospheric drift which were not considered in IRI-1979.

The experimental data from 23 stations in the Northern Hemisphere were obtained between 1957 and 1970. The worldwide coverage in geographic latitude is 7°N to 71°N (7.5° to 64.1° geomagnetic) and O° to 131°E geographic longitude.

We have developed appropriate procedure which allow us to infer from these data the main parameters of the global ionospheric motions at E- and F-region levels.

An algorithm for computing the zonal and meridional drift components VX, VY can be found in IRI-1990.

The last version of the computer programm called DRIFT which does the test calculation of Ionospheric Drifts Global Model whith printing the tables at the Epson printer is written in Turbo ascal for the IBM PC AT 286/287 compatible computers. Program code (execute module) is about 25 Kbyte. Data files are about 10 Kbyte.

E- and F-region horizontal ionospheric irregularities drift data, worldwide obtained from 1957 to 1970 by D1 and D3 methods, are statistically analysed and a computer code for the average velocity variations in latitude and local time for some solar activity levels is constructed. The PC program DRIFT allows to determine zonal and meridional drift velocities of ionospheric irregularities at the lower (90 < h < = 140 km) and upper (h > 140 km) ionosphere.

The main block of the program DRIFT is the procedure DRIRR for calculating VX and VY for a period (P), geomagnetic (geographic) latitude (FI) and local time (LT) to be specified.

The example of the program DRIFT calculation for F-region (REG=2) and for the whole period of observations (P=1) is in Table. VX > 0 to east, VY > 0 to north. FI is geomagnetic latitude.     

国际参考电离层模型输出参数峰值高度性能

电离层峰值高度H_mF₂是描述电离层形态的重要参数之一,国际参考电离层模型IRI-2016中融入了大量电离层测高仪和无线电掩星探测数据,用以提升H_mF₂的预测精度.本文利用太阳活动低年（2007—2010年）气象、电离层和气候卫星联合观测系统COSMIC探测数据描述全球范围内COSMIC H_mF₂的三维形态变化,对比分析了IRI-2016与IRI-2012模型的预测结果,同时分析了IRI-2016模型输出H_mF₂的性能.结果表明,IRI模型在中高纬度地区的输出结果高于COSMIC反演结果,而赤道及低纬地区则大都偏低.与IRI-2012模型相比,IRI-2016模型的输出结果在夜间至凌晨时段呈现较为明显的纬向梯度变化且大部分区域输出值偏高,但在白天时段赤道附近区域的输出值大都偏低.上述结果为电离层IRI模型的完善提供了一定参考.      

The quiet nighttime low-latitude ionosphere as observed by TIMED/GUVI

In this paper, we examine the nighttime ionosphere climatology structure in the low latitude region and discrepancies between Global Ultraviolet Imager (GUVI) observations and the IRI model predictions using (1) the magnetic zonal mean of electron number density as a function of altitude and magnetic latitude, (2) vertical electron density profiles at various levels of F10.7 index, (3) nighttime descent and magnitude decrease of the ionosphere, (4) point-to-point comparisons of F-peak height (hmF2) and density (NmF2), and (5) the magnetic longitudinal variations of hmF2 and NmF2. The data collected from the Thermosphere, Ionosphere, Mesosphere, Energetics, and Dynamics (TIMED) mission since its launch in December 2001 have provided great opportunities for many scientific investigations of the ionosphere. In this analysis, we investigate the climatology of the nighttime low-latitude ionosphere under low geomagnetic activity (kp ? 4) using the electron density profiles inferred from the airglow measurements obtained by the GUVI aboard the TIMED spacecraft and compared with the results obtained from IRI (International Reference Ionosphere) model-2001. The observed climatology is an essential tool for further understanding the electrodynamics in the low-latitude region and improving the model’s prediction capability. The time range of the GUVI data used in this study is from 2002 (day 053) to 2006 (day 304), and the IRI model predictions were produced at every GUVI location. The ionosphere observed is generally of greater density than what IRI predicts throughout the night for all four seasons for low and moderate solar activity while the model over-predicts the electron density near the F-region peak at high solar activity before midnight. Observations show that the height of the F-region peak has a steep descent from dusk to midnight and near midnight the height of layer is insensitive to solar conditions, significantly different than what is predicted by IRI. Longitudinal features shown in GUVI data are present in the low-latitude ionosphere after sunset and continue through to midnight after which the low-latitude ionosphere is largely zonally symmetric.     

Importance of electric field measurement over low latitudes at stratospheric heights by balloons

The vertical field in the stratosphere around 35 km is predominantly of atmospheric origin whereas the horizontal electric field at these altitude is mainly of ionospheric origin. The electrical coupling between ionosphere and atmosphere is not known for low latitudes. Balloon borne electric field measurements are planned from Hyderabad, India (geographic latitude 17.5° N) to understand this coupling. Measurement of stratospheric electric fields are also important from the point of view of the sun-weather relationship. It si suggested that the balloon borne electric field measurements are important to understand the electrodynamics of the middle atmosphere.     

Evaluation of the IRI-2016 and NeQuick electron content specification by COSMIC GPS radio occultation,ground-based GPS and Jason-2 joint altimeter/GPS observations

We examined performance of two empirical profile-based ionospheric models, namely IRI-2016 and NeQuick-2, in electron content (EC) and total electron content (TEC) representation for different seasons and levels of solar activity. We derived and analyzed EC estimates in several representative altitudinal intervals for the ionosphere and the plasmasphere from the COSMIC GPS radio occultation, ground-based GPS and Jason-2 joint altimeter/GPS observations. It allows us to estimate a quantitative impact of the ionospheric electron density profiles formulation in several altitudinal intervals and to examine the source of the model-data discrepancies of the EC specification from the bottom-side ionosphere towards the GPS orbit altitudes. The most pronounced model-data differences were found at the low latitude region as related to the equatorial ionization anomaly appearance. Both the IRI-2016 and NeQuick-2 models tend to overestimate the daytime ionospheric EC and TEC at low latitudes during all seasons of low solar activity. On the contrary, during high solar activity the model results underestimated the EC/TEC observations at low latitudes. We found that both models underestimated the EC for the topside ionosphere and plasmasphere regions for all levels of solar activity. For low solar activity, the underestimated EC from the topside ionosphere and plasmasphere can compensate the overestimation of the ionospheric EC and, consequently, can slightly decrease the resulted model overestimation of the ground-based TEC. For high solar activity, the underestimated EC from the topside ionosphere and plasmasphere leads to a strengthening of the model underestimation of the ground-based TEC values. We demonstrated that the major source of the model-data discrepancies in the EC/TEC domain comes from the topside ionosphere/plasmasphere system.     

极光强扰动对中低纬电离层的影响

本文考查了120°E附近的五个中低纬电离层观测站在极光强扰动下的f₀F₂行为。共考查了从1966—1970年五年资料中AE>1400日及1969年中AE>1000日的f₀F₂行为。研究得出了与印度站链有所不同特征——在极光强扰动下120°E中低纬五站之f₀F₂均有不同程度的减小,而不是增加,并且在中纬较高纬度的满州里站之f₀F₂减小比北京站要显著。扰日后效在中、低纬区不同,低纬之武昌、广州和海南岛三站均呈现扰动过后次日上午段的f₀F₂增加,中纬较高纬度的满洲里站仍呈现f₀F₂减少。我们认为这是由于低纬区主要受赤道喷泉效应改变的影响,而中纬及亚极光纬区主要受极光强扰时产生的环球电场的直接作用结果,它反映了纬向电场耦合传递的影响。当然极光扰动时对中性大气层的能量输入亦对观测到的现象有贡献。      

GPS derived ionospheric TEC response to geomagnetic storm on 24 August 2005 at Indian low latitude stations

Results pertaining to the response of the low latitude ionosphere to a major geomagnetic storm that occurred on 24 August 2005 are presented. The dual frequency GPS data have been analyzed to retrieve vertical total electron content at two Indian low latitude stations (IGS stations) Hyderabad (Geographic latitude 17°20′N, Geographic longitude 78°30′E, Geomagnetic latitude 8.65°N) and Bangalore (Geographic latitude 12°58′N, Geographic longitude 77°33′E, Geomagnetic latitude 4.58°N). These results show variation of GPS derived total electron content (TEC) due to geomagnetic storm effect, local low latitude electrodynamics response to penetration of high latitude convection electric field and effect of modified fountain effect on GPS–TEC in low latitude zone.     

低纬地区夜间电离层底部电子浓度与磁扰的关系

本文利用100kHz的低频无线电波资料,计算分析了1986—1987年期间,几种不同磁扰情况下,低纬地区夜间电离层中100km以下区域积分电子浓度及其变化的起因.结果表明:该区域电子浓度的变化与地磁扰动关系密切.在磁静日期间,其值较小,且随磁扰而变化,但比磁扰滞后1到2天.在磁暴后,其值较大,会出现几次剧烈起伏.该区域积分电子浓度的起伏可大于一个量级.沉降电子产生的动致辐射可能是引起该区域电子浓度变化的主要原因之