中国地震科学实验场BDS-3定位精度和地壳运动初步分析

Preliminary analysis to positioning precision and crustal movement of BDS-3 data recorded by the China seismic experiment site

我国BDS-3卫星导航系统于2020年7月建成,并为全球用户提供服务,自此开始,中国地震科学实验场(简称“实验场”)的GNSS测站相继接收BDS-3卫星数据,目前已经积累了2年多的观测数据,为BDS-3应用于川滇地区地壳运动监测提供了重要平台和数据保障。为评估实验场BDS-3观测数据的精度及其应用于地壳监测的可行性,本文首先根据各测站所记录的BDS-3的B1I和B3I两个频点的多路径效应和信噪比与卫星高度角之间的关系,对BDS-3的数据质量进行评价。然后,基于高精度数据处理软件GAMIT/GLOBK (10.7版)对各测站同期记录的BDS-3和GPS数据分别进行处理,得到BDS-3和GPS坐标时间序列。基于包括线性项、年周期项和半年周期项等分量的函数模型,利用极大似然法分别对BDS-3和GPS时间序列进行拟合估计,得到各测站的线性速度、年周期和半年周期信号,并对拟合结果对比分析,评定BDS-3和GPS的定位精度。最后,讨论BDS-3定位精度的影响因素和BDS-3水平速度场的区域性特征。研究表明:实验场BDS-3与GPS原始数据质量相当,BDS-3坐标时间序列的均方根残差(RMS)的平均值在N、E、U方向上分别为4.42、4.25和8.34 mm,稍大于GPS的结果。BDS-3与GPS速度场在E方向存在约2.0 mm/a系统性差异。在区域分布特征方面,BDS-3和GPS的速度场、周年期和半年信号没有明显差别。认为目前影响BDS-3定位精度的因素主要为卫星轨道产品不够完善,经验型太阳光压模型和卫星天线相位中心改正模型等欠缺。造成BDS-3和GPS速度场差异的原因主要为两者的定位基准不一致。随着实验场BDS-3观测数据的积累和数据解算模型的改进,BDS-3可望达到GPS的定位精度,并形成独立于GPS的监测系统,为该区地壳运动监测和地震预测提供优质的大地测量产品。

The BDS-3 navigation satellite system of China was completely accomplished in July 2020,then starting to provide services for global users.GNSS stations in the China seismic experiment site(CSES)have been receiving BDS-3 satellite data ever since,and accumulated observational data for more than 2 years,providing an important platform in acquiring observational data for the application of BDS-3 in exploring crustal movement in Sichuan-Yunan area.To assess the current precision of the BDS-3 positioning and its performance in crustal movement monitoring,we first evaluate the quality of BDS-3 observational data according to the relationship of multi-path effect and signal-to-noise ration with elevation angles.Using GAMIT/GLOBK(version 10.7),we have processed the simultaneously recorded BDS-3 and GPS data separately to obtain coordinate time series for each station.Fitting the time series of three coordinate components separately with a functional model which encompasses linear,annual,semi-annual and other terms by the maximum probability estimation method,we obtain velocity,amplitude and phase for E,N and U components of the coordinate time series.Furthermore,we evaluate the precision of BDS-3 and GPS by comparative analysis of the fitting results.Finally we discuss the possible factors which could influence the positioning precision of BDS-3,and regional features of the horizontal velocity field derived from BDS-3 observations.The results show that the quality of raw data for BDS-3 observations is comparable with GPS data.The data fitting for BDS-3 and GPS time series shows that the average value of root mean square(RMS)of the BDS-3 residual time series are 4.42,4.25 and 8.34 mm for the E,N and U components,respectively,larger than those of GPS data.Systematic difference is identified of about 2 mm/a in E direction between velocity fields of BDS-3 and GPS.The velocity fields,and the annual and semi-annual signals derived from BDS-3 and GPS data do not show obvious differences in regional distribution.We think that currently the factors affecting the positioning precision of BDS-3 are the relatively lower precision of satellite orbit and clock difference products,the shortage of empirical solar pressure and satellite antenna phase center correction for BDS-3 and so on.The difference between the velocity fields of BDS-3 and GPS is due to the inconsistence of their reference frames.We expect that,with the continuous accumulation of BDS-3 observational data and the improvement of the data processing models,the positioning precision of BDS-3 will enhance with time,and the BDS-3 will be used independently from GPS to provide geodetic products of high-precision for monitoring crustal movement at CSES.