利用单频多GNSS观测值同步估计VTEC和卫星DCB的算法研究

In the context of GNSS-based applications, Vertical Total Electron Content (VTEC) is one of the key parameters for ionosphere monitoring, while satellite Differential code biases (DCB) account for one type of correction that is of necessity to the realization of services including precise positioning. At present, the single- and dual-frequency schemes employing, respectively, “code-minus-phase” and “geometry-free” linear combinations, can both serve the needs of VTEC estimation with complementary advantages. Single-frequency scheme corresponds to fairly low expense in relation to receiver hardware. At the same time, dual-frequency scheme is in support of joint estimation of satellite DCB, along with VTEC. ..With these facts in mind, this proposal presents a so-called “modified single-frequency scheme”: its point of departure is the single-frequency, multi-GNSS observations that have been corrected using the precise satellite orbit and clock products, in which information about the satellite DCB shall show up; its key technique is the realization of Kalman-filtered-based “single-frequency, multi-GNSS” uncombined precise point positioning (PPP), serving as a tool for extracting the ionospheric delays; its main feature is the possibility of joint estimation of VTEC and satellite DCB; its advantage is low hardware expense and simple software implementation. ..The outcomes of this proposal shall enrich the model and applicability of uncombined PPP, and further GNSS data processing theory. In the meantime, they can also provide a novel idea for GNSS-based ionosphere monitoring, and contribute a new method to multi-GNSS (including Chinese BDS) satellite DCB calibration.

在全球导航卫星系统（GNSS）应用中，垂向总电子含量（VTEC）是电离层反演的一类重要参数，卫星差分伪距偏差（DCB）则是实现精密定位等服务的一类必要改正。分别采用单频“伪距减相位”和双频“无几何影响”组合观测值的单、双频方案均可用于估计VTEC，且优点互补：单频方案的接收机硬件成本低，双频方案能同步估计卫星DCB。为此，本项目提出一种“单频改进方案”：其出发点是经精密卫星轨道和卫星钟差改正后的单频多GNSS非组合观测值，其中包含了卫星DCB信息；其核心技术是实现“单频多GNSS”非组合PPP的滤波算法，作为获取电离层斜延迟的手段；其特色是可同步估计VTEC和卫星DCB；其优势是硬件投入少、软件实现简单。研究成果将可丰富非组合PPP的模型，拓展非组合PPP的应用，发展GNSS数据处理理论；也可为GNSS电离层反演提供新思路，为包含我国BDS在内的多GNSS卫星DCB标定贡献新方法。

从以我国北斗卫星导航系统为代表的GNSS（Global Navigation Satellite System）观测数据中获取的VTEC（Vertical Total Electron Content）和SDCB（Satellite Differential Code Bias）两类参数可分别应用于大气电离层反演和精密导航定位授时。本项目开展了基于单频多模观测数据同步估计VTEC和SDCB的方法研究。研究内容包括：首先，构建单频多模观测方程，特色在于借助参数重整方法消除若干类参数线性相关引起的秩亏问题。其次，实现了单频多模非组合PPP（Precise Point Positioning）滤波算法，用于（近）实时地提取电离层斜延迟参数，并随后将其输入至薄层假设模型，最终得到了VTEC和SDCB估值。研究结果包括：一、基于最小二乘方差分量估计方法分析了不同类型测地型接收机的单频多模数据，准确构建了顾及精度、互相关和时间相关等性质的单测站观测值随机模型，并率先分析了全球首款支持北斗三号的TRIMBLE-ALLOY接收机的数据质量；二、基于低成本UBLOX接收机的单频多模实测数据，实现了VTEC和多模SDCB的高精度估计，各类估值的RMS量级分别为0.5 TECu（VTEC）、0.2-0.5 ns（GPS-SDCB）、0.4-0.7 ns（GLONASS-SDCB）、0.3-0.5 ns（GALILEO-SDCB）和0.5-1.0 ns（BDS-SDCB）；三、提出了一种能准确分离RDCB（Receiver Differential Code Bias）短时变化趋势的改进平滑伪距方法，分析了全球近400个IGS（International GNSS Service）跟踪站的多频多模数据，发现近三成跟踪站的RDCB存在显著的天内变化，且该变化的主要影响因素是天线的环境温度。科学意义包括：发展了GNSS数据处理理论，精化了PPP模型算法，为实现高反演精度、低硬件成本的大气电离层研究提供了新思路，为北斗等GNSS-SDCB标校贡献了新方法。