基于空间变异特性的格网电离层延迟估计方法

广域增强系统采用格网模型校正用户电离层延迟误差,为保证理想的校正效果,必须精确估计格网点电离层延迟。电离层延迟的空间相关性是完成这一估计的理论依据。针对传统反距离加权法因不能准确描述这种空间相关性而使得估计效果受限的问题,依据空间统计学原理建立了电离层延迟空间变异函数模型,提出一种新的权值计算方法,并通过实际观测数据进行了仿真验证。结果表明,相比于传统方法,这一方法能明显改善格网点电离层延迟估计效果,尤其在穿透点观测数据稀疏的区域,其改善效果更为明显。     

基于BDS-2/BDS-3联合处理的北斗超快速钟差预报优化策略

针对北斗卫星导航系统(BDS)钟差预报产品无法满足高精度快速服务需求的现状，提出了一种基于BDS-2/BDS-3联合估计的超快速卫星钟差预报优化策略。区别于传统两步法预报模型，利用稀疏建模方法一步求解所有模型项，并通过BDS-2/BDS-3星间相关性实现了模型系数解的增强；为进一步降低模型残差的影响，基于残差序列时空相关性，利用半变异函数重构了模型估计的权阵。为验证提出的钟差预报模型，设计了12套对比方案，实验结果表明：基于稀疏建模的钟差模型参数一步估计可略微提高钟差预报精度；通过引入星间相关性对随机模型进行精化，钟差序列一步建模可分别将BDS-2与BDS-3卫星钟差18h预报精度提升28.6%与27.2%；基于半变异函数建模的模型残差相关性提取，可实现BDS-2与BDS-3预报钟差精度8.0%与11.1%的提升。因此，提出的优化策略对当前北斗超快速卫星钟差预报产品精化具有重要意义。     

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.     

On the estimation of regional covariance functions of TEC variations over Canada

Spatial and temporal variations of Total Electron Content (TEC) can affect GNSS high accuracy positioning. Enhanced estimation of ionospheric variations and their de-correlation can benefit differential and point positioning rapid solutions. Global and regional TEC maps can provide the overall state of ionopsheric variations in space and time domains within their accuracy limits. In this paper, these maps are exploited to retrieve ionospheric variations by means of variograms and their associated covariance functions of TEC residuals over Canadian region during geomagnetically quiet and disturbed conditions. A number of theoretical variogram functions are reviewed for modeling covariance of TEC residuals. The variogram modeling of residuals during a strong geomagnetic storm revealed variances of one order of magnitude larger compared to a rather quiet condition. Variogram models are also used in regional and local kriging interpolation experiments and their performances are evaluated. Global maps of TEC RMS by International GNSS Service and two of its analysis centres are also compared over the Canadian region during a two-year period. Realistic representation of regional variances using estimated variograms when compared to global ionospheric RMS maps are also presented.