基于单站多系统的GNSS硬件延迟估算方法及其应用

随着全球导航卫星系统(Global Navigation Satellite Systems,GNSS)的不断发展,中国地区单个GNSS接收站在一个时刻可以接收到超过30颗GNSS卫星的信号,这为单站GNSS硬件延迟估算方法的研究提供了有利条件.本文首先通过GNSS硬件实验,分析了不同温度条件下GNSS系统硬件延迟的变化特征,研究结果显示:当温度快速变化时,硬件延迟变化比较剧烈,变化幅度可达12.53TECU(1TECU=10 16el·m-2);在恒温条件或室温条件下,硬件延迟变化比较缓慢,变化幅度在1.00TECU左右.在GNSS系统硬件延迟实验的基础上,充分利用单站多星观测的特点,提出了一种基于单站多系统的GNSS硬件延迟的估算方法——单站三角分解与差分消元法,并将该方法应用于河北保定站2015—2017年GNSS系统硬件延迟的求解中.通过对估算的GNSS系统硬件延迟进行分析显示:单站三角分解与差分消元法具有计算速度快、独立性好的特点;在北斗系统上硬件延迟的求解效果优于GPS、GLONASS系统,硬件延迟求解的结果整体上比利用欧洲定轨中心全球电离层地图校正的结果大2.50~3.00TECU左右;同时,该方法在消除GNSS系统硬件延迟后,获得的垂直总电子含量(Total Electron Content,TEC)能较好地反映电离层TEC的周日变化、日出增强、半年变化、年变化和春秋分不对称性等特征.

应用经验正交函数估算顶部电离层电子密度剖面

本文基于IRI模型、地面数字测高仪和GNSS TEC数据,提出了一种利用经验正交函数(Empirical Orthogonal Function,简称EOF)估算顶部电离层电子密度剖面的方法,并将其应用于美国Millstone Hill测高仪和GNSS数据以估算顶部电离层电子密度剖面.通过将估算的临界频率、峰值高度、400km以上电子密度分别与测高仪实测临界频率、测高仪实测峰值高度以及非相干散射雷达实测400km以上电子密度作对比以对方法的有效性进行验证.统计结果显示估算临界频率、峰值高度与测高仪实测数据基本一致,400km以上估算电子密度相较于非相干散射雷达实测的绝对误差平均值仅是测高仪推算400km以上电子密度绝对误差平均值的一半左右.所以本文提出的方法可以更加精确地估算顶部电离层电子密度.

火星电离层电子浓度昼夜变化特性研究

本文利用MAVEN卫星Langmuir Probe and Waves(LPW)仪器的在轨电子浓度探测数据,研究了火星电离层电子浓度随太阳天顶角(Solar Zenith Angle,SZA)的变化以及昼夜电子浓度变化的异同.基于2014年至2017年期间MAVEN的电子浓度数据,我们发现:在200km以下,白天电离层电子浓度主要受光化学平衡控制,由于白天光电离过程使得昼夜电子浓度差异较大,此时电离层昼夜传输能影响到的最大范围约在SZA=110°;而在200km以上,白天电离层受输运过程控制,此时昼夜电子浓度差别较小,电离层昼夜间电子浓度变化较为缓慢.通过研究MAVEN在deep-dip(低高度深入探测)期间的电子浓度数据,我们发现火星磁场会显著影响夜间200km以下的电子浓度分布结构,强磁场中闭合磁力线对电子沉降过程的阻碍作用使得在夜间该区域的电子浓度小于相邻区域.同时,通过比较deep-dip期间昼夜电子浓度随高度的变化,发现夜间电子沉降作用的影响可能主要集中在160km以下.

Recent Progresses on Ionospheric Climatology Investigations

The ionosphere varies over multiple time scales,which are classified into two categories: the climatology and weather variations.In this national report,we give a brief summary of recent progresses in ionospheric climatology with focus on(1) the seasonal variations,(2) solar cycle effects, and(3) empirical modeling of the ionosphere.The seasonal variations of the ionosphere have been explored in many works to give a more detailed picture with regional and global features at various altitudes by analyzing the observation data from various sources and models.Moreover,a series of studies reported the response of the ionosphere to solar cycle variations,which revealed some novel and detailed features of solar activity dependence of ionospheric parameters at different altitudes. These investigations have improved our understanding on the states of the ionosphere and underlying fundamental processes,provided clues to future studies on ionospheric weather,and guided ionospheric modeling,forecasting and related applications.

A Simulation of the Mid-and Low-latitude Ionospheric Electric Fields

A theoretical model of ionospheric electric fields at mid-and low-latitudes is developed.In the geomagnetic dipolar coordinate system,the ionospheric dynamo equations were solved,and the ionospheric electric potential and electric field were derived respectively.Major parameters for the model inputs,such as the neutral winds,the densities and temperatures of electron,ions and neutrals,are obtained from empirical models.The global ionospheric electrical potential and field at mid-and low-latitudes derived from our model are largely in agreement with the results presented by other authors and the empirical model.Using our model,it is found that the diurnal component of the HWM93 wind mainly contributed to the formation of the vertical electric field,while the semidiurnal component mainly contributed to the zonal electric field.Finally,by adjustment of the input F region winds and conductivities,most discrepancies between our model and the empirical one can be eliminated,and it is proved that the F region dynamo is the most significant contribution to the electric fields.

A Review of the Ionospheric Investigations in China:Progress During 2008-2010

In the ionospheric research,various progresses have been made during the last two years.This paper reviews the recent works of Chinese scientists.For convenience,the contents include:ionospheric storms and space weather;ionospheric irregularities and scintillation;ionospheric variability;ionospheric disturbances;ionospheric response to solar eclipses;ionospheric coupling with atmosphere and lithosphere;ionospheric climatology;ionospheric modeling;and ionospheric prediction and application.

Some Investigations on the Ionosphere during 2012–2014 in China

In this national biannual report, we will outline some recent progresses in ionospheric studies conducted by Chinese scientists since 2012. The mentioned aspects include: the solar activity control of the ionosphere; couplings between the ionosphere, lower atmosphere and plasmasphere;ionospheric climatology and disturbances; ionospheric irregularities and scintillation; models, data assimilation and simulations; unusual phenomena of the ionosphere; possible seismic signatures presented in ionospheric observations, and some methodology progresses. These progresses will enhance our ability to observe the ionosphere, provide more reasonable understanding about the states of the ionosphere and underlying fundamental processes, and stimulate ionospheric modeling, forecasting and related applications.

A Review on the Ionospheric Research:Chinese Works During 2006—2008

This paper reviews various progresses on the ionospheric studies by the scientists in China during the last two years.The main contents concern the 4 aspects of the ionospheric re-search:(1) ionospheric weather and coupling with magnetosphere(polar and auroral ionosphere,ionospheric response to substorms,ionospheric storms);(2) mid-and low-latitude ionospheric clima-tology(ionospheric properties,yearly variations and solar activity dependence,long term variation);(3) ionospheric coupling with neutral atmosphere(gravity waves,tides,planetary waves,background upper atmosphere,and ionospheric response);and(4) ionospheric diagnostics(observation,modeling,and prediction).

Preclinical pharmacology study of neutral myocardial imaging agent ^(99m)TcN(NOEt)_2

To explore the biological properties of a new neutral myocardial imaging agent 99mTcN（NOEt）2,preparation and characterization of 99mTeN（NOEt）2, kinetics of blood-drug clearance in rabbits, biodistribution in rats, test of undue toxicity in mice and myocardial imaging in dogs were performed and volunteer imaging. Radiochemical purity of 99mTeN（NOEt）2 was over than 90% and stable for 6 hours at room temperature. Blood disappearance was analyzed with biexponential model, T1/2（α）=2.53 min, T1/2 （β）=330 min and Cl=378 mL/h were obtained. Biodistribution studies demonstrated that 99mTcN（NOEt）2 localized selectively in myocardium of rats. Cardiac uptake were 2.79, 2.25, 2.00 and 1.88%ID/organ at 5, 30, 60 and 90min of postinjection, respectively. The heart-to-lung activity ratio was 1.16 at 60 min. Images showed that pulmonary uptake decreased faster than cardiac uptake in a dog. The mean heart-to-lung activity ratios in a dog were 1.69, 2.40 and 2.55 at 10, 30 and 60min of postinjection, respectively. The heart was distinguishable on scans at 30min. Whole body imaging showed that cardiac uptake was 2.82%ID at 90min, but hepatic uptake was 30%ID and remained constant. The test of undue toxicity showed that the dose received by mice was 614 times as by human. Volunteer imaging suggests 99mTcN（NOEt）2 redistribution with time. 99mTcN（NOEt）2 exhibited favorable stabilities, biological properties and safety. It is worth for further studying in human.

从深空探测大国迈向行星科学强国

自伽利略1609年将望远镜指向星空迄今,已逾400年。1959年苏联“月球2号”首次抵达月球,开启深空探测时代。1969年美国“阿波罗11号”首次载人登月,催生建立行星科学。纵观人类深空探测60年,先后出现两次探测热潮、两个深空探测大国(美国、苏联)。苏联领先又衰落,仅留给历史一个深空探测大国的背影,而美国成功转型为深空探测强国,至今在世界行星科学最前沿领航。探索浩瀚宇宙,是全人类的共同梦想。作为正在发展中的深空探测大国,我国应该怎样立足国情,走出一条有中国特色的行星科学强国之路?文章参照历史,梳理现状,畅想未来,给出我们的思考:大力培养行星科学人才,尽快实现科学引领深空探测。

2017年5月磁暴过程及近地空间环境响应分析

世界时间2017年5月27日15:37,地磁场开始发生强烈扰动,达到大磁暴水平.分析显示, 5月23日的日冕物质抛射(CME)在行星际空间形成磁云,其携带的行星际磁场南向分量持续12 h小于-10 nT,最小达到-20.71 nT.长时间强南向磁场分量与磁层顶地磁场相互作用,地磁场发生强扰动, SYM-H指数最小达到-142 nT.全球多个电离层台站监测到电离层扰动.综合电离层测高仪、TIMED-GUVI观测和模式同化TEC数据分析表明,此次电离层暴具有南北半球不对称性,大气成分(N2, O2)扰动很可能是此次电离层负暴的主要原因,赤道向热层风抬升或者O/N2的升高是正暴的可能原因.磁暴期间热层大气密度增加,引起低轨道航天器从29~30日开始轨道衰减速度显著加快,与HPI有很好的对应关系.

Solar activity effects of the ionosphere: A brief review

Solar radiation, which varies over multiple temporal scales, modulates remarkably the evolution of the ionosphere. The solar activity dependence of the ionosphere is a key and fundamental issue in ionospheric physics, providing information essential to understanding the variations in the ionosphere and its processes. Selected recent studies on solar activity effects of the ionosphere are briefly reviewed in this report. This report focuses on (1) observations of solar irradiance at X-ray and extreme ultraviolet wavelengths and the outstanding problems of solar proxies, in the view of ionospheric studies, (2) new findings and improved representations of the features of the solar activity dependence of ionospheric key parameters and the corresponding physical processes, (3) possible phenomena in the ionosphere under extremely high and low solar activity conditions that are unique, as indicated by historical solar datasets and the deep solar minimum of solar cycle 23/24, and (4) statistical studies and model simulations of the ionosphere response to solar flares. The above-mentioned studies provide new clues for comprehensively explaining basic processes in the ionosphere and improving the prediction capability of ionospheric models and related applications.

Modeling the global ionospheric total electron content with empirical orthogonal function analysis

In the present work we model the global ionospheric total electron content (TEC) with the analysis of empirical orthogonal functions (EOF). The obtained statistical eigen modes, which makeup the modeled TEC, consist of two factors: the eigen vectors mapping TEC patterns at latitude and longitude (or local time LT), and the corresponding coefficients displaying the TEC variations in different time scales, i.e., the solar cycle, the yearly (annual and semiannual) and the diurnal universal time variations. It is found that the EOF analysis can separate the TEC variations into chief processes and the first two modes illustrate the most of the ionospheric climate properties. The first mode contains both the semiannual component which shows the semiannual ionospheric anomaly and the annual component which shows the annual or non-seasonal ionospheric anomaly. The second mode contains mainly the annual component and shows the normal seasonal ionospheric variation at most latitudes and local time sectors. The annual component in the second mode also manifests seasonal anomaly of the ionosphere at higher mid-latitudes around noontime. It is concluded that the EOF analysis, as a statistical eigen mode method, is resultful in analyzing the ionospheric climatology hence can be used to construct the empirical model for the ionospheric climatology.

The first time observations of low-latitude ionospheric irregularities by VHF radar in Hainan

Sanya VHF radar (18.4°N, 109.6°E, dip latitude 12.8°N) at Hainan Island is the first coherent backscatter radar for sounding low-latitude ionospheric irregularities in the mainland of China. In this paper, we present the first results of low-latitude ionospheric E and F region irregularities using the radar data during the period from February 2009 to March 2010. The Doppler velocity of radar echoes from E region field aligned irregularities (FAIs) was about several tens of meters per second, while the Doppler spectral width was appreciably larger than the velocity, and could reach one hundred meters per second, indicating that the observed E region FAIs belonged to type 2 irregularities. The observations of range time intensity (RTI) maps of FAIs showed that E region irregularities most often occurred at night within the altitude range 85-115 km, and were rarely observed at afternoon hours. The percentage occurrence of E region FAIs maximized during spring months (Feb.-May) with a peak value over 80%. The heights at which the strongest echo related FAIs occurred were mainly around 100 km, lower than h'Es and the difference is mostly 10-20 km. December solstice seemed to be the minimum period of occurrence when the FAI echoes were commonly detected at a narrow altitude range 90-100 km. Moreover, simultaneous radar and GPS observations during spread F events in the pre-midnight hours of solar minimum revealed that significant GPS L band scintillations coincided with the appearance of F region plasma plume structures, which extended up to 450 km in altitude.

A comparison of mesospheric winds measured by FPI and meteor radar located at 40N

In this paper, winds derived from OH Meinel 892.0 nm detection by an FPI (Fabry-Perot Interferometer) are compared with the simultaneous wind measurements from a meteor radar during April-May of 2010. The peak height of OH Meinel 892.0 nm is about 87 km. The variations of FPI wind at 87 km mostly have the similar track to meteor radar wind at 87 km, and the data values of FPI wind mainly fall into the range of meteor radar wind. However, there are still quantitative differences between the observations of the two systems. The best cross-correlation occurs in meridional winds from two systems in April of 2010. An obvious wave signal with 0.2 cycle/d frequency is found in meridional winds observed by both FPI and meteor radar.

Enhanced anti-sunward flow near local noon during a period of horizontal IMF and high solar wind velocity V_Y

It is believed that a southward interplanetary magnetic field (IMF) is mainly responsible for the energy input from solar wind into the magnetosphere.This paper presents an unusual case of strong anti-sunward plasma flow (up to 2 km/s) in the polar cap ionosphere and large cross-polar cap potential (CPCP) during a period of horizontal IMF (|BZ| < 2 nT) observed by both ACE (at the L1 point) and Geotail (on the dusk flank of the magnetosheath).The CPCP is even higher than that under preceding BZ ≈-23 nT.Furthermore,GOES8 observed that the magnetosheath field turns northward as the anti-sunward plasma flow and CPCP start to increase,which implies that the magnetosheath field interacting with the Earth's magnetopause has significantly rotated and differs from the IMF observed by ACE and Geotail.In accordance with previous theoretical work,we suggest that the magnetic field line draping produces a southward magnetosheath field and enhances anti-sunward plasma flow and the CPCP.

Recent investigation on the coupling between the ionosphere and upper atmosphere

Scientific attention has recently been focused on the coupling of the earth's upper atmosphere and ionosphere. In the present work, we review the advances in this field, emphasizing the studies and contributions of Chinese scholars. This work first introduces new developments in the observation instruments of the upper atmosphere. Two kinds of instruments are involved: optical instruments(lidars, FP interferometers and all-sky airglow imagers) and radio instruments(MST radars and all-sky meteor radars). Based on the data from these instruments and satellites, the researches on climatology and wave disturbances in the upper atmosphere are then introduced. The studies on both the sporadic sodium layer and sporadic E-layer are presented as the main works concerning the coupling of the upper atmosphere and the low ionosphere. We then review the investigations on the ionospheric longitudinal structure and the causative atmospheric non-migrating tide as the main progress of the coupling between the atmosphere and the ionospheric F2-region. Regarding the ionosphere-thermosphere coupling, we introduce studies on the equatorial thermospheric anomaly, as well as the influence of the thermospheric winds and gravity waves to the ionospheric F2-region. Chinese scholars have made much advancement on the coupling of the ionosphere and upper atmosphere, including the observation instruments, data precession, and modeling, as well as the mechanism analysis.

Correlation between ionospheric longitudinal harmonic components and upper atmospheric tides

There is strong correlation among the ionospheric longitudinal structures of wavenumber-3(WN3),wavenumber-4(WN4),and eastward-propagating diurnal tides with zonal wave numbers s = 2 and 3(DE2 and DE3) in the upper atmosphere.The total electron content derived from the Global Ionospheric Maps of the Jet Propulsion Laboratory is used to deduce the latitudinally total electron content(ITEC) in the low-latitude ionosphere,and TIDE/TIMED observations are employed to obtain zonal and meridian winds of the mesopause and lower thermosphere.Through Fourier transformation,various ionospheric longitudinal harmonic components and tidal patterns are derived from the ionospheric and upper-atmospheric observations,and we compare the annual/inter-annual variations in ionospheric harmonic components WN3 and WN4 with those in atmospheric tides(DE2 and DE3).It is found that the annual and inter-annual variations in WN3 and WN4 are consistent with those in DE2 and DE3 zonal wind components respectively,while they are inconsistent with those in the meridian components.We then decompose the harmonic components into "tidal patterns",finding that the "DE2" and "DE3" patterns are the main parts of WN3 and WN4 respectively.Their annual and inter-annual variations are similar to those of atmospheric tidal patterns(DE2 and DE3).Complex correlation results show that correlation between the ionospheric "DE2" in WN3 and the atmospheric tidal DE2 zonal wind component is quite strong in the Northern Hemisphere,while that between the ionospheric "DE3" in WN4 and the atmospheric tidal DE3 zonal wind component is much stronger at low latitudes.At the same time,the contribution of the meridian wind component is very weak.Above all,the atmospheric tidal DE2 and DE3 patterns are important factors of the ionospheric WN3 and WN4 structures.

A theoretical model for mid-and low-latitude ionospheric electric fields in realistic geomagnetic fields

The geomagnetic fields,which play important roles in the ionospheric dynamo,can greatly affect the global distribution of ionospheric electric fields,currents and other ionospheric electrodynamics phenomena.In the study of ionospheric electrodynamics phenomena,such as the longitudinal variations of ionospheric electric fields,the non-dipolar component of the geomagnetic fields must be taken into account.In this paper,we deduce a theoretical electric field model for ionospheric dynamo at mid-and low-latitude which adopt a modified magnetic apex coordinates system.In the new electric field model,the geomagnetic fields can be calculated from either the IGRF model or the dipole field model,and the neutral winds and conductivities are calculated based on empirical models.Then the dynamo equation for the electric potential is finally solved in terms of the line-by-line iteration method,and the ionospheric electric fields and currents are derived from the calculated potential.Our model can reproduce the main features of the ionospheric electrodynamics processes,so it will be a useful tool for the investigation of the upper atmosphere and ionosphere.

Development of a middle and low latitude theoretical ionospheric model and an observation system data assimilation experiment

On the basis of previous work, we develop a middle and low latitude theoretical ionospheric model in this paper, named Theoretical Ionospheric Model of the Earth in the Institute of Geology and Geophysics, Chinese Academy of Sciences (TIME-IGGCAS). TIME-IGGCAS solves the equations of mass continuity, motion and energy of electron and ions self-consistently and uses an eccentric dipole field approxima-tion to the Earth’s magnetic field. We combine the Eulerian and Lagrangian approaches in the model and take account of the plasma E×B drift velocity. Calculation results reveal that the model is steady and credible and can reproduce most large-scale features of ionosphere. By using TIME-IGGCAS, we carried out an observation system data assimilation experiment. Assimilation results show that the E×B drift velocity can be accurately estimated by ingesting the observed foF2 and hmF2 into the model ap-plying nonlinear least-square fit method. We suggest that this work is of great significance in the de-velopment of ionospheric data assimilation model to give better nowcast and forecast of ionosphere.