基于北斗GEO卫星双频观测值连续监测电离层延迟

利用北斗GEO卫星观测数据直接计算电离层延迟。由于GEO卫星具有固定穿刺点和静地的特性,使得观测站监测电离层变化时可不考虑空间变化,并可进行连续不间断监测。通过分析北斗GEO卫星三种频率码伪距和载波相位观测值不同组合,选取B1&B2双频计算电离层延迟为最优组合,采用相位平滑伪距的方法计算电离层延迟TEC,相较其他电离层模型,该方法的优点是不会引入模型误差,可得到连续的高精度的电离层延迟监测结果。     

北斗区域Klobuchar改进模型及其修正精度分析

北斗卫星导航系统采用Klobuchar模型修正单频接收机用户的电离层延迟误差,由于此模型从亚洲地区应用角度考虑,在某一特定区域的修正精度甚至不足50%。为进一步提高区域电离层延迟修正精度,提出在原模型8个改正参数的基础上增加5个关键参数的Klobuchar改进模型,并采用松弛迭代与直线搜索法中的黄金分割相结合的算法对新增参数进行求解。以天津及其附近区域为例,利用GPStation6接收机采集到的实测数据对改进模型与原模型进行计算。将国际全球导航卫星系统服务组织（International GNSS Service,IGS）发布的全球电离层格网数据作为参考值,对比分析改进模型与原模型的修正精度。结果表明,区域Klobuchar改进模型在天津及其附近区域的电离层延迟平均修正精度比原模型提升了10.46%,平均修正精度达到77.51%。     

北斗三号系统广域差分服务精度评估

为了保证北斗系统广域差分服务的平稳过渡，北斗三号系统（BDS-3）通过GEO卫星B1I/B3I信号播发北斗二号协议广域差分改正信息，包括等效钟差改正数与格网点电离层信息。分析了增加BDS-3卫星后，等效钟差改正数和格网点电离层信息的特征，并对BDS-2和BDS-3的用户差分距离误差（UDRE）进行了对比。联合BDS-2和BDS-3实测数据，对BDS-3广域差分服务定位精度进行了评估。分析结果表明:BDS-2卫星广播星历空间信号用户等效距离误差（UERE）约为1 m，经过等效钟差改正数后，用户差分距离误差约为0.3 m；BDS-3卫星广播星历空间信号用户等效距离误差约为0.4 m，经过等效钟差改正数后，用户差分距离误差约为0.2 m。等效钟差改正数可以修正广播电文更新带来的空间信号阶跃误差，显著提升卫星空间信号精度。与基本导航系统播发的Klobuchar 8模型，广域差分系统所播发的格网点电离层信息可将电离层误差修正精度提高约18%。与单独BDS-2卫星相比，BDS-2/BDS-3卫星联合条件下，基本导航的单频用户和双频用户定位精度可分别提升26%和41%；广域差分服务的单频用户定位精度为2.4 m，双频用户定位精度为1.7 m，单频用户和双频用户定位精度分别提升13%和41%。      

基于空间统计方法的电离层折射修正技术

针对中国上空电离层所具有的特殊性和GPS观测站在中国西部分布相对稀疏的特点, 尝试探索中国卫星增强系统电离层时延信息修正技术, 为卫星导航定位以及遥感、遥测等空间应用工程的电波修正提供数据. 利用中国地壳形变监测网提供的双频GPS数据, 以空间统计方法为主要工具, 给出了普通Kriging电离层估计算法, 构建了平静期和磁暴期电离层理论变异模型, 详细分析了电离层折射修正的精度. 结果表明, 将空间统计方法应用于卫星增强系统中的电离层时延改正问题, 有利于提高增强系统的电离层折射修正精度, 特别是在观测样点相对较少的情况下, 有利于系统完整性的实现.      

单接收机GNSS数据组合硬件延迟的联合求解方法

利用GNSS观测数据解算TEC的最大误差源是硬件延迟,包括卫星硬件延迟和接收机硬件延迟.在单接收机情况下,由于数据稀疏以及接收到的卫星信号时间不对齐等特点,已有的解算硬件延迟方法的求解结果往往不理想.在应用局域模式拟合方法和SCORE方法求解单接收机数据基础上,利用局域模型拟合法在电离层平静期拟合较准确的优点,提出一种联合改进方法,同时改正了SCORE方法解算过程中约束过强的缺点.通过利用GPStation-6接收机的GPS和BDS实际观测数据进行解算分析,验证了所提方法的有效性与准确性.      

实时电离层格网数据精度评估

电离层延迟是制约单频接收机定位精度的重要误差源之一.为提高单频接收机的实时电离层改正精度,需要实时电离层数据.以中国科学院空天信息创新研究院提供的实时电离层数据为例,对比分析不同太阳活动期实时电离层数据及预报电离层数据与IGS最终电离层数据之间的差值以及不同太阳活动期、不同纬度测站的电离层数据对电离层延迟进行改正后得到的定位精度.结果表明:在低太阳活动期和高太阳活动期,实时电离层数据无法很好地反映大部分海洋上空的电离层变化特性;对不同太阳活动期,实时电离层数据在高纬度测站的定位精度优于预报数据和广播模型,在中纬度测站的定位精度略低于预报数据而与广播模型定位精度相当,在低纬度测站的定位精度略优于预报数据和广播模型.      

利用北斗观测数据实时监测中国区域电离层变化

北斗卫星导航信号采用三个频点工作,可以利用伪距双频组差方法解算电离层电子含量,为实时监视中国区域电离层变化提供新的技术手段.中国中低纬度处于电离层赤道异常变化区,在北纬20°±5°区域时常发生较大梯度的电离层变化.利用北斗实时多频伪距和相位观测数据,采用相位平滑伪距方法计算电离层穿刺点电子含量,分析通过北斗系统GEO卫星监测的电离层周日变化特性;采用多面函数方法拟合中国区域1°×1°分辨率的电离层延迟量,每5min绘制一幅中国区域电离层图,观测区域所有电离层穿刺点拟合残差RMS为2.778TECU;分析北斗系统实时监测中国区域电离层异常情况,当发生电离层异常变化时,相邻两天的VTEC（Vertical Total Electronic Content）峰值相差约60TECU.      

全球电离层地图TEC数据的插值算法

由IGS工作组提供的全球电离层地图(GIM)是电离层重要的应用数据.卫星高度计能够提供全球实时的电离层延迟误差校正.利用GIM数据,以Jason-3时空分辨率进行电离层总电子含量(TEC)的时间维度插值和空间维度插值,其中空间维度插值采用了Kriging插值和双线性插值两种方法.针对两种插值方法得到的总电子含量,与平滑...     

一种地基GNSS接收机差分码偏差估算方法

GNSS不同频点间的码伪距作差会引入信号的差分码偏差(DCB),包括GNSS卫星及地面接收机的DCB.本文提出一种地基GNSS接收机差分码偏差参数估算方法,首先由电离层文件参数作线性插值,计算出电离层延迟误差.之后对IGS站观测文件进行加权最小二乘法估计,得到GPS卫星和地面GNSS接收机的L1C频点和L2P频点间码偏...     

北斗星基增强系统性能评估

以实际广播星历、精密星历和北斗星基增强系统(BDSBAS)增强报文为实验数据，通过计算BDSBAS轨道误差、卫星钟差、空间信号测距误差和BDSBAS格网电离层有效点、播发时间和电离层延迟误差6个指标，评估分析了BDSBAS空间信号的性能。结果显示：BDSBAS增强后的GPS卫星轨道误差在切向、法向、径向分别降低了34.57%,40.57%,30.90%；卫星钟差均方根降低了24.31%，卫星钟差标准差降低了16.8%；空间信号测距误差相比增强前降低了32.75%;BDSBAS格网电离层有效点覆盖了中国及周边地区；BDSBAS各点电离层延迟播发间隔均达到ICAO对精确差分定位的要求；电离层延迟在0°-5°N范围内误差在0.4 m以上，可信度均达到99.9%，在5°-55°N范围内误差小于0.4 m，可信度均为100%;BDSBAS水平定位误差提升超过25%，垂直定位误差提升超过50%，完好性均在99.9%以上。     

Klobuchar电离层模型误差分析及预测

电离层延迟误差是全球导航卫星系统(global navigation satellite system,GNSS)中的重要误差源之一.目前在电离层延迟改正模型中,应用最广泛的是Klobuchar参数模型,但是该模型的改正率仅能达到60％左右,无法满足日益增长的精度需求.将国际GNSS监测评估系统(internation...     

SHAKING: Adjusted spherical harmonics adding KrigING method for near real-time ionospheric modeling with multi-GNSS observations

Precise positioning based on Global Navigation Satellite System (GNSS) technique requires high accuracy ionospheric total electron content (TEC) correction models to account for the ionospheric path delay errors. We present an adjusted Spherical Harmonics Adding KrigING method (SHAKING) approach for regional ionospheric vertical TEC (VTEC) modeling in real time. In the proposed SHAKING method, the VTEC information over the sparse observation data area is extrapolated by the Adjusted Spherical Harmonic (ASH) function, and the boundary distortion in regional VTEC modeling is corrected by the stochastic VTEC estimated using Kriging interpolation. Using real-time GPS, GLONASS and BDS-2/3 data streams of the Crust Movement Observation Network of China (CMONOC), the SHAKING-based regional ionospheric VTEC maps are re-constructed over China and its boundary regions. Compared to GNSS VTECs derived from the independent stations, the quality of SHAKING solution improves by 13–31% and 6–33% with respect to the ASH-only solution during high and low geomagnetic periods, respectively. Compared to the inverse distance weighting (IDW) generated result, significant quality improved of SHAKING-based VTEC maps is also observed, especially over the edge areas with an improvement of 60–80%. Overall, the proposed SHAKING method exhibits notable advantage over the existing regional VTEC modeling techniques, which can be used for regional TEC modeling and associated high-precision positioning applications.     

IGS电离层产品在双向时间频率传递中的应用

利用IGS组织提供的全球电离层资料对卫星双向时间频率传递中的电离层误差进行修正。IGS提供特定时刻、固定经纬度网格点上的电离层总电子含量。对该电离层资料首先进行空间四点网格内插,然后利用双线性内插得到电离层穿刺点所需时刻的总电子含量,最后将得到电离层数据经过处理用于双向时间频率传递修正。结果表明：电离层对C波段的影响在（0～0.5）ns范围内,这对亚纳秒量级的时间比对是必须考虑的。IGS提供的电离层产品适合应用于双向时间频率传递,具有方法简单、准确度高和价格低廉等特点。     

Kalman filter based estimation of differential hardware biases with triangular interpolation technique for IRNSS

Ionosphere delay correction is the main error correction to the computation of single frequency user position using satellite navigation. However ionosphere delay consists of not only delay but also frequency dependent differential hardware biases from satellite and receiver ends. For ionosphere point of view, Indian Regional Navigation Satellite System (IRNSS) service area comes in equatorial anomaly region. It is a unique satellite navigation system which operates at L5 and S frequencies and consists of Geostationary Earth Orbit (GEO) and Geo Synchronous Orbit (GSO) satellite constellation. With IRNSS measurements availability, there is a good opportunity to estimate and analyse differential hardware biases with GEO/GSO combination and with equatorial ionosphere variation. In this paper, Kalman filter based estimation with triangular interpolation technique is used to estimate differential hardware biases for all IRNSS satellites and reference receivers at L5 frequency. The standard deviation of the 15?days of daily estimation of satellite differential hardware biases is in the range of 0.32 to 1.17 TECU for all IRNSS satellites. Similarly, the standard deviation of the 15?days of daily estimation varies up to 2.85 and 6.0 TECU for receiver differential hardware biases during calm and stormy period respectively. The ionosphere delay computed using estimated differential hardware biases is compared with Global Ionosphere Map (GIM) data. A rigorous analysis is carried out to study the error in the estimation in terms of input data noise level, satellite constellation and effect of latitude. Our result reveals that over IRNSS service area, there is an exponential increase in the error in the estimation of receiver differential hardware biases with respect to latitude.     

观测站稀疏地区的WAAS电离层时延网格修正算法

在改进的广域增强系统电离层时延网格算法的基础上，给出了针对观测量比较少的地区比较适用的电离层时延网格修正算法，并通过模拟数据和GPS实测数据与原方法进行了分析比较．结果表明，在观测站稀疏的情况下，本文的计算方法模式的精度比原方法有较大的提高．     

Comparison of observed ionospheric vertical TEC over the sea in Indian region with IRI-2016 model

The vertical ionospheric TEC values obtained from GAGAN grid based ionospheric delay correction values over the sea in the Indian equatorial region have been compared with the corresponding values derived from the International Reference Ionosphere model, IRI-2016. The objective of this work is to study the deviation of the vertical TEC derived from the IRI model from ground truths over the sea for different conditions. This will serve the basic intention of assessing the candidature of the IRI model as an alternative ionospheric correction model in navigation receivers in terms of accuracy. We have chosen different solar activity periods, seasons, geomagnetic conditions, locations etc. for our comparison and analysis. The TEC values by the IRI-2016 were compared with the actual measured values for the given conditions and errors were obtained. The measured vertical TEC values at the ionospheric grid points were derived from the GAGAN broadcast ionospheric delay data and used as reference. The IRI model with standard internal functions was used in estimating the TEC at the same ionospheric grid points. The errors in the model derived values are statistically analysed. Broadly, the results show that, for the Indian sector over the sea, the IRI model performs better on quiet days in off equatorial regions, particularly in the northern region. The overall performance degrades for other conditions with the model generally underestimating the true TEC values and most severely in the equatorial region. The performance is worst in this region for the disturbed days of the equinoctial period. The comparison study is also done with the TEC data measured directly by dual frequency GPS receivers. The results were found to be in general agreement with those obtained by comparing the model with GAGAN broadcast data as reference. This study will be useful in considering the IRI-2016 model for real time estimates of TEC as an alternative to the current parametric model in a satellite navigation receiver in absence of other options.