热膨胀效应对GNSS基准站垂向位移非线性变化的影响

天线观测墩及基岩的热膨胀效应会造成GNSS基准站坐标时间序列高程方向的非线性变化。本文提出了一种计算热膨胀效应导致的基准站垂向位移的改进方法:首先利用基岩热膨胀模型和基准站地表温度数据,分别计算热膨胀效应对基准站天线观测墩和基岩的影响量;其次,利用最小二乘拟合方法,同时估计模型中周期项的周期、振幅、相位等信息,而已有方法仅估计振幅与相位信息;最后,基于改进的模型,分析了基准站垂向位移的周期性特征变化。本文利用该方法分析了有代表性的9个IGS基准站的数据。结果表明:基岩热膨胀和天线观测墩热效应能造成测站垂直方向位移变化;在分析的基准站中,最大影响分别可达0.57mm和1.85mm;热膨胀效应造成的GNSS基准站垂直方向位移时间序列具有周年和半周年周期特性,分别可以解释测站U方向坐标时间序列季节性变化的11.2%和3.3%,影响大小随测站纬度的增加而增加,且半周年影响明显小于周年影响;同时,部分测站发现了其他小周期的影响(约51d)。此外,基于该方法,选取了全球107个IGS站,计算了热膨胀造成的各测站垂向位移周年振幅及其相位,结果显示周年振幅最大可达3.3mm,其大小和测站纬度具有比较明显的相关性。

Impact on Nonl inear Vertical Variation of GNSS Reference Stations Caused by Thermal Expansion

Thermal expansion of GPS monuments and nearby bedrock could result in vertical changes in the coordinate time series of GNSS reference stations.In this paper,an improved method was developed to compute the magnitude of vertical variations caused by thermal expansion.Fi rstly,we calculated the effect on GPS monument and bedrock caused by thermal expansion based on land surface temperature data of GNSS reference stations and thermal expansion model.Secondly,we estimated the ci rcular frequencies, ampl itudes and phases using the method of least squares fitting instead of the current method which estimated only the ampl itudes and phases information.Final ly,we studied the periodic characteristics of the vertical variations caused by our modified thermal expansion model.Through analyzing the results of 9 representative IGS stations,we concluded that thermal expansion of GPS monuments and nearby bedrock could result in vertical variations of GNSS stations.The maximum variations could reach up to 0.57 mm and 1.85 mm at these stations respectively.The vertical variation caused by thermal expansion exhibited both annual and semiannual characteristics,which could explain 11.2% and 3.3% of the total annual and semi-annual variations in the up component of the coordinate time series respectively,and the magnitudes became larger with the increasing of thei r latitudes.Meanwhi le,the ampl itudes of the annual variations were much larger than that of the semi-annual variations.Meanwhi le,some other smal l period (about 51 days)was also detected at some of these stations.In addition,we chose 107 IGS reference stations and computed the annual ampl itudes and phases caused by thermal expansion of al l these stations based on the method aforesaid.The results show that the maximum annual ampl itude can reach to 3.3 mm,and thei r magnitudes show positive correlation with thei r latitudes prominently.