区域GPS网实测电离层变化和卫星硬件延迟的可靠性研究

根据高精度卫星导航定位的实际需要,介绍了利用中国GPS区域网双频相位平滑伪距实测数据,准实时监测区域网电离层电子总含量(TEC)变化和GPS卫星硬件延迟(DCB)的方法和结果.着重研究了区域网独立测定DCB的可靠性,利用中国境内的GPS站点分别构造了3个大小不同的区域网,通过实测DCB和垂直电子总含量(VTEC)与CO...     

IGS产品在GPS时间比对中的应用

在利用GPS CV(GPS Common View)技术进行高精度时间比对时，电离层和卫星位置误差对观测到的卫星信号的影响是不容忽视的，需要对它进行精确的估计和改正．讨论IGS精密星历和CODE全球总电子含量图(TECMAPs)在GPS时间传递中的应用．计算结果表明，采用IGS产品可有效提高单站定时和远距离时间传递的精度。     

GPS实时监测和预报电离层电子含量

GPS能高精度地实时监测电离层总电子含量(TEC)变化，对纠正单频GPS接收机电离层延迟和监测电离层活动及其所反映的太阳活动规律具有重要意义．上海地区GPS综合应用网的建立，为监测长江三角洲地区电离层变化提供了宝贵的资料，利用这些双频GPS接收机的连续观测资料，可近实时地监测和预报该地区电离层总电子含量，其内外符精度和外推预报30分钟的精度均优于0.4m．     

利用Bernese5.0软件实现LEO卫星精密定轨

越来越多的LEO卫星装载了高精度的星载GPS接收机,星载GPS定轨已成为LEO卫星精密定轨的重要手段之一。星载GPS精密定轨精度依赖于GPS星历及钟差精度,采用CODE(Center for Orbit Determination in Europe)官方网站提供的GPS精密星历及钟差数据,基于瑞士伯尼尔大学开发的Bernese 5.0软件,采用非差减缩动力学定轨方法,解算了60天的CHAMP卫星和SAC-C卫星轨道,并将所得轨道与JPL和GFZ事后科学轨道比较,得出的轨道位置三维精度优于20 cm量级,速度三维精度约为0.20 mm/s。     

GIM在LEO卫星单频GPS定轨中的应用

电离层延迟误差是单频GPS(Global Positioning System)数据最主要的误差源,为提高基于单频GPS数据的LEO(Low Earth Orbiting)卫星定轨精度,必须消除/减弱GPS观测数据中电离层延迟影响.研究了全球电离层模型GIM(Global IonosphericMaps)在基于单频GPS伪距数据的低轨卫星运动学和动力学定轨中的应用,并通过估算电离层尺度因子的方法消除C/A码伪距观测量中电离层延迟影响.由于LEO卫星星载GPS信号受电离层延迟影响与卫星轨道高度相关,选取了轨道高度在300～800 km的CHAMP(CHAllenging Mini-satellite Payload)、GRACE(Gravity Recovery AndClimate Experiment)、TerraSAR-X及SAC-C等LEO卫星C/A码伪距观测量作为试算数据.CHAMP等卫星实测数据计算结果表明:以JPL(Jet Propulsion Laboratory)发布的GIM模型作为背景模型,通过电离层比例因子法能很好地消除C/A码伪距观测量中电离层延迟影响,提高LEO卫星运动学和动力学定轨精度,其中,CHAMP卫星轨道最低,受电离层延迟影响最严重,定轨精度提高最显著,分别为55.6%和47.6%;SAC-C卫星轨道高度最高,受电离层延迟影响最小,相应的定轨精度提高幅度也最低,分别为47.8%和38.2%.     

融合IGS和CMONOC的GPS数据反演实测电离层研究

利用国际卫星导航系统服务以及中国大陆构造环境监测网络的实测数据,构建电离层球谐模型SHAG(Shanghai Astronomical Observatory global model),并与欧洲定轨中心(Center for Orbit Determination in Europe,CODE)提供的电离层数据比较,得到如下结果:1)在全球范围内,二者解算的卫星硬件延迟误差的均方根值(root mean square,RMS)为0.11 ns,观测站硬件延迟误差的RMS为0.59 ns;2)对于中国大陆及邻区,二者电离层总电子含量(total electronic content,TEC)的RMS为2.1 TECu(1 TECu=0.35 ns),但SHAG模型解算观测站TEC更接近GNSS双频解算的结果;3)通过与数字测高仪的观测资料比较,发现SHAG模型解算的电离层结果可较好地描述不同观测站区域的电离层变化趋势。综合结果表明,中国大陆构造环境监测网络数据的大量引入改善了SHAG模型的中国区域电离层特性,能较好地描述中国区域电离层空间分布及变化特征。     

北斗星地双向时频传递与广广播钟差精度分析

与其他卫星导航系统不同,北斗卫星导航系统采用星地双向时间比对技术,直接测量卫星钟相对于地面保持的系统时间的钟差,并用于广播电文钟差参数的建模。讨论了电离层延迟误差、卫星相位中心误差等不同误差源对不同类型卫星双向时间同步卫星钟差精度的影响。实测数据分析结果表明,星地双向卫星钟差内符合精度(RMS)优于0.15 ns。利用双向卫星钟差序列,对广播星历钟差参数预报精度进行了分析,统计结果显示广播电文钟差参数预报1 h,精度在2 ns以内,移动卫星刚入境时,钟差参数预报6 h误差可达10 ns。     

电离层TEC对GRB041227的响应

2004年12月27日世界时21时30分,一个非常强的γ射线暴扫过地球,它使得暴露在这次事件中的地球高层大气产生额外电离.在爆发期间,地球上多个甚低频(VLF)电波台站都同时观测到了电离层突然骚扰(SID)事件.对GOES卫星的X射线数据、ACE卫星的太阳风和行星际数据以及理论分析表明,地球上观测到的SID事件是由GRB041227引起的.另外,利用国际GPS服务网(IGS)提供的观测数据,采用相干求和的数据处理方法研究了电离层总电子含量(TEC)对这次γ射线暴的响应.结果表明,SGR1806-20产生的GRB041227对地球电离层产生了明显的影响.在爆发期间,平均电离层TEC有一定的增加,其最大增加值约0.04TECU(1TECU=10~(16)el/m~2),产生效果与一个C级或者低于C级的太阳耀斑相当.计算结果还表明了遥远的天体也能对地球的近地空间环境产生或多或少的影响.     

利用时间序列模型预报电离层TEC

以IGS(international GPS service)发布的电离层TEC(total electron content)资料为样本,用时间序列模型对全球的电离层总电子含量进行了预报.在时间序列预报模型中,不同的定阶方法导致不同的预报结果;实践证明本文使用的BIC定阶准则较好地实现了电离层总电子含量的预报.结果表明:对10 d左右的预报时间段,时间序列模型的TEC计算结果相对精度高,预报相对精度优于60%的网格点数在总网格点数中所占百分比可达90%以上.     

BDS-2导航电文的TGD参数精度及其对用户导航定位精度的影响

北斗二号(Bei Dou Navigation Satellite System-2, BDS-2)卫星播发以B3频点为基准的卫星钟差参数,并播发B1和B2频点相对于B3频点的群延迟(time group delay, TGD)参数。以差分码偏差(differential code bias, DCB)参数为基准,计算BDS-2群延迟参数的精度。在计算过程中,发现在2017年年积日202 d以前,各颗卫星TGD1参数精度较差,与DCB1参数互差在2～4 ns之间,TGD2与DCB2的互差约为0.5 ns。在2017年年积日202―203 d处,所有卫星群延迟参数均发生明显跳变,该跳变主要是因参与群延迟解算的北斗系统的接收机不再采用抗多径算法所致。跳变后,群延迟参数与MGEX (Multi-GNSS Experiment)公布的差分码偏差参数的差值小于0.5 ns,与GPS卫星播发的群延迟参数精度接近。进一步利用实测数据计算了群延迟参数改正精度对用户导航定位精度的影响。结果表明,使用跳变前的群延迟参数,单频定位精度为2.078 m,双频定位N方向精度为1.451 m,E方向精度为1.648 m,U方向精度为3.467 m;使用跳变后的群延迟参数,单频定位精度为1.968 m,双频定位N方向精度为1.361 m,E方向精度为0.998 m,U方向精度为2.789 m,在双频定位的N, E, U方向,双频定位精度分别提升6.2%, 39.4%, 19.5%。     

电离层TEC对小耀斑的响应

利用国际GPS观测网(IGS)提供的多个台站的观测数据,分析了M级别以下的小、暗太阳耀斑对向阳面电离层TEC的影响．利用传统分析方法的结果表明,从单条视线(LOS)观测数据得到的电离层TEC及其时间变化率曲线来看,由于它们的波动水平和正常情况下的背景电离层变化相当,使此类小耀斑的信息完全淹没在背景噪声中,不能够显示和分辨出耀斑的发生．利用相干求和的数据处理方法,选用向阳面18个GPS台站的观测数据研究了一次C级SF耀斑引起的电离层TEC增加,结果发现,这种方法能有效地消除背景电离层变化噪声,电离层对耀斑的响应非常清楚和明显,这通常只能在X级别的大耀斑中看到．和GOES卫星X射线数据相比,电离层TEC变化的时间特征和耀斑爆发的开始、最大和结束时间均有很好的符合,其最大平均TEC增量在0．1TECU以下,和X级别的大耀斑相比有一个或多个量级上的差别．     

Evaluation of LEO based GPS slant TEC using a simulation technique

With the increased number of low Earth orbit (LEO) satellites equipped with Global Positioning System (GPS) receiver, the LEO based GPS slant total electron content (STEC) data play a more important role in ionospheric research due to better global coverage. The accuracy of LEO TEC is hardly evaluated by comparison with the independent TEC measurement simultaneously. We propose an approach based on the simulated data to verify the accuracy of TEC determination. The simulated data (i.e., the pseudorange and carrier phase observations) was generated based on the consideration of the effect of the ionosphere, the so-called differential code bias (DCB) and observational noise. The errors of carrier phase to code leveling process and DCB estimation are analyzed quantitatively. Also, the effect of observational noise, solar activity and LEO orbit altitude on the accuracy of TEC determination will be discussed in detail. The accuracy of TEC determination is relative to solar activity and LEO orbit altitude, the higher LEO orbit and lower F10.7 index, the higher accuracy of TEC determination. It is found by the first time that, with the amplification of the pseudorange noise, the accuracy of leveling process and TEC determination declines almost linearly. With the LEO missions in the near future, it is hoped that the GPS satellite DCBs estimated based on LEO observations would be better than those based on ground-based observations.     

Study of total electron content variations over equatorial and low latitude ionosphere during extreme solar minimum

In recent years with the advancement in satellite based navigational applications, study of Total Electron Content (TEC) has gained significant importance. It is well known that due to dynamical behaviour of equatorial and low latitude ionosphere, the levels of ionization is relatively high herein. The sustained decrease in solar extreme ultraviolet radiations during the current minimum is greater than any in recent history. This gives us the opportunity to study the observations of global positioning system total electron content (GPS-TEC) dual frequency signals from the GPS satellites continuously recorded at Trivandrum (an equatorial station) and Delhi (a low latitude station) during the extremely low solar activity period from January 2007 to June 2009. This study illustrates the diurnal, seasonal and annual variations of TEC during the extended solar minimum period. This study also investigates the behaviour of daytime ionosphere around spring and autumn equinoxes at low solar activity period. The results clearly reveal the presence of equinoctial asymmetry which is more pronounced at equatorial station Trivandrum. The diurnal variation of TEC shows a short-lived day minimum which occurs between 0500 to 0600 LT at both the stations. Delhi TEC values show its steep increase and reach at its peak value between 1200 and 1400 LT, while at the equator the peak is broad and occurs around 1600 LT. Further, the daily maximum TEC ranges from about 5 to 40 TEC units at Trivandrum and about 10 to 40 TEC units at Delhi, which correspond to range delay variations of about 1 to 8 m at the GPS L1 frequency of 1.575 GHz. The Maximum values of TEC were observed during spring equinox rather than autumn equinox, showing presence of semi annual variation at both the locations. The minimum values of TEC were observed during the summer solstice at Trivandrum indicating the presence of winter anomaly at equatorial region while Delhi TEC values were minimum during winter solstice showing absence of winter anomaly. Also the TEC values at both the locations have been decreasing since 2007 onwards exhibit good positive correlation with solar activity.     

A Study on the Reliability of the Ionospheric VTEC and Satellite DCB Derived from a Regional GPS Network

According to the requirement of high-precision satellite navigation, we have introduced the method for the quasi-realtime monitoring of variations of the regional ionospheric total electron content (TEC) and GPS satellite differential code bias (DCB), based on the dual-frequency carrier-phase smoothed pseudorange data obtained from a regional GPS network in China. Especially, we have studied the feasibility of retrieving DCB independently from the regional GPS networks with different sizes. For this purpose, 3 regional networks based on the countrywide GPS stations are investigated. The comparisons of the computed DCB and VTEC(vertical total electron content) with those of CODE(the Center for Orbit Determination in Europe) indicate that in order to realize a reliable quasi-realtime measurement of DCB by a regional network, there is a certain requirement on the size of the regional network, and that the relative accuracies of the quasi-realtime VTEC and DCB measured by using a Chinese GPS regional network can reach 2.0TECu and 0.25 ns, respectively.     

GPS共视时间比对中的电离层时延改正问题

众所周知，GPS共视是目前国际上主要的时间传递比对技术，其中扣除电离层时延是很重要的一个方面。介绍了如何采用国际GPS服务中心(IGS-International GPS Service)公布的电离总电子含量(TEC-Total Electron Content)图来进行电离层时延改正。结果表明：对于单频GPS接收机，采用TEC图作电离层时延改正后的单站定时和共视比对精度比用理论模型作改正的精度有很大的提高。通过比较还表明，亚太地区的时间实验室之室的时间传递精度比欧美地区的要低，这可能是因为亚太地区用于测量TEC的IGS测站少，因而导致该地区的TEC的精度较低。     

GPS监测电离层活动的方法和最新进展

全球定位系统(GPS)可以快速、准确地提供电离层总电子含量(TEC)信息。简要介绍了GPS技术精确测量TEC、监测电离层的原理和方法，指出进行TEC绝对量估计时求解差分群延迟(DCB)的重要性，以及建立多层和实时电离层监测模型的必要性。分析了影响TEC估计的主要误差源，着重介绍了目前GPS监测电离层的最新成果和进展。     

Comparison of total electron content obtained from GPS with IRI

The comparison of the IRI model with TEC estimated using the continuous GPS observations of European part of IGS network is considered. The variability of a measured TEC was analyzed for the low solar activity in the period 1996–1997. We used IRI 90 version with upped height limit 2000 km and IRI 95 up to 1000 km. It is shown that the difference between model and measured TEC depends on latitude and season.Generally, IRI 95 underestimate and IRI 90 overestimate the TEC relative to GPS measurements. The relative difference may reach over 50%.