GPS基准站坐标时间序列中呈现显著的非线性运动特征。研究造成非线性运动的成因，有助于正确解释测站运动的物理机制和建立更为精确的测站运动模型，进而更好地应用于大地测量及地球动力学研究，具有重要的科学意义及应用价值。本项目拟以全球GPS基准站为研究对象，深入研究环境负载与热膨胀效应对GPS坐标时间序列的非线性运动影响。结合GPS观测值精度，评价全球及区域环境模型精度；研究融合多种环境模型建立最优负载位移时间序列的新方法；精化标石和基岩热膨胀模型造成的垂直地表位移，并建立热膨胀模型与水平位移的数值联系；采用最新的GPS数据处理模型及策略对全球IGS站数据进行一致性重新处理，建立更为"干净"的GPS坐标时间序列，并根据本项目获得的环境负载及热膨胀效应位移时间序列对其进行非线性修正，进一步提高环境负载与GPS坐标时间序列的匹配度。研究成果可为地球参考框架的建立与维持及相关的地学研究提供理论支持。

GPS coordinate time series exhibit significant non-linear variation characteristics. To investigate the factors that cause the non-linear motion of stations is of important scientific significance and practical value. It is very helpful to reasonably interpret physical mechanism of stations' motions and establish more accurate motion model. Thus GPS coordinate time series can be better applied to geodesy and geodynamics research. This project will take the global GPS reference stations as objects, make a deep insight into the effects of environmental loading and thermal expansion on the non-linear variations of GPS coordinate time series. Taking advantage of the precision of GPS observables, the quality of the existing global and regional environmental models will be evaluated. Then a new method of generating optimum loading time series using various environmental models will be proposed to correct the non-linear displacements of GPS reference stations. An improved 3-D surface displacement model caused by GPS monument and bedrock thermal expansion will be established to further interpret and weaken the non-linear signals in the GPS coordinate time series. Finally, global IGS reference station data will be reprocessed using state of the art GPS data processing models and strategies to obtain a more "clean" GPS coordinate time series. The environmental loading and thermal expansion displacement time series obtained from this project will then be implemented to correct the non-linear variation of the reprocessed GPS time series to further improve the consistency between environmental loading predictions and the displacement of the IGS reference stations. Results of this project will provide theoretic support for the establishment and maintenance of terrestrial reference frame, together with related geo-science researches.