二阶电离层延迟对GPS PPP时间传递的影响

Influence of the second-order ionospheric delay on GPS PPP time transfer

针对精密单点定位时间传递观测模型无法消除二阶电离层延迟误差的实际问题,推导了顾及二阶电离层延迟误差修正的观测模型。应用两个时段实测数据,比较分析了二阶电离层延迟改正前与改正后的精密单点定位测站钟差和时间传递结果。分析表明,二阶电离层延迟对低纬度地区测站钟差影响显著,对中、高纬度的影响逐渐减弱;测站钟差差异序列呈固定偏差加周日变化,固定偏差在南北半球符号相反。二阶电离层对长基线时间传递的影响最大超过26皮秒,对短基线的影响基本可以忽略。据此,提出亚纳秒级长基线时间传递进行二阶电离层延迟修正是必要的,特别是组成基线的测站位于低纬度地区。

In view of the practical problem that the second-order ionospheric delay error(Ion2)is not corrected in Precise Point Positioning(PPP)time transfer,the PPP observation equation with the Ion2 is derived.The PPP clocks and time transfer with and without the Ion2 correction are compared and analyzed using two test periods.Based on the measured data,analysis shows that the influence of the Ion2 on the PPP clocks at a low-latitude are more significant than that of mid-latitude and polar regions.The difference series of PPP clock solutions shows fixed deviation plus some diurnal variations,and the sign of fixed deviation is opposite in the northern and southern hemispheres.The maximum influence of the Ion2 on the long time-links transfer can be up to more than 26ps,but for the short time-links,it can be ignored.Therefore the Ion2 correction is necessary for sub-nanosecond PPP time transfer over long time-links,especially when the time-links are made by the stations located in low-latitude regions.