不同太阳活动条件下电离层形态对估算GPS系统硬件延迟的影响

利用两个中纬度台站GPS观测数据提取的GPS卫星硬件延迟,分析了不同太阳活动情况下估算的硬件延迟稳定性和统计特征,结合同期电离层观测数据,研究了电离层状态对硬件延迟估算结果的影响.研究结果表明,基于太阳活动高年(2001年)GPS观测数据估算的硬件延迟稳定性要低于太阳活动低年GPS观测数据的估算结果,利用2001年GPS数据估算的卫星硬件延迟年标准偏差(RMS)平均值约为1TECU,而2009年GPS数据估算的卫星硬件延迟年标准偏差平均值约为0.8TECU.通过对2001年和2009年北京地区电离层F₂层最大电子密度(N_mF₂)变化性分析,结合GPS硬件延迟估算方法对电离层时空变化条件的要求,认为硬件延迟稳定性与太阳活动强度的联系是由不同太阳活动条件下电离层变化的强度差异引起的. 

Influence of Ionospheric Variability in Solar Maximum and Solar Minimum Period on the Stability of Estimated GPS Instrumental Biases

It is an important step to estimate the GPS instrumental biases in the process of calculating the ionospheric Total Electron Content (TEC) from GPS data, and the estimation of GPS instrumental biases is the main source of errors in the GPS observed TEC. Therefore, study of the estimated instrumental biases is helpful for understanding the accuracy of ionospheric TEC derived from GPS observation. In this paper, data from two mid-latitude GPS stations was used to derive the instrumental biases of GPS satellites in solar maximum and minimum periods. The stability and statistical characteristics of estimated instrumental biases observed at BJFS and URUM stations in 2001, 2007 and 2009 are given. The influence of ionospheric morphology on the estimation of GPS instrumental biases was studied by analyzing the ionospheric data in the same periods. By comparing the estimated GPS instrumental biases under different ionospheric condition, the accuracy and usability of GPS observed ionospheric TEC were analyzed. Results show that the stability of estimated instrumental biases using GPS data from solar maximum period (in 2001) is poorer than that from solar minimum period (in 2007 and 2009). The yearly RMS value of estimated instrumental biases in 2001 is about 1TECU, and the yearly RMS value is about 0.8TECU in 2007 and 2009. In view of hypothesis in the process of calculating the ionospheric TEC, combining with the analysis of variability of ionospheric critical frequency observed at Beijing station, it is believed that the connection between stability of estimated instrumental biases and the solar cycle phase is related with the differences of ionospheric variability in solar maximum and minimum. Study on the stability of estimated instrumental biases indicates that the accuracy of ionospheric TEC derived from GPS observation is different in different solar cycle phase, and the error of ionospheric TEC caused by instrumental biases of the satellites is about 1TECU.