毫米级、非线性、自洽的地球参考架和地球定向参数的模型研究

Considering the deficiencies such as the inadequate precision and stability of International Terrestrial Reference Frame (ITRF), the inconsistency between the long-term solution of Earth Orientation Parameters (EOP C04) and ITRF, etc., IAU and IAG organized the Workgroup of Earth Rotation Theory is to provide a new theory and product of EOP to be consistent with ITRF and ICRF. We propose to investigate a new mathematical model for simultaneous estimation of TRF and EOP by taking not only the correlation information between each technique-specific reference frame and its EOP but also non-linear temporal behavior of both fiducial stations and frame datum into account and the products of millimeter-level non-linear TRF and EOP, including seasonal signal existing in the time series of each station position, will be published online regularly. 1) By using of intra-technique combined solutions of SLR, VLBI, GNSS and DORIS, local ties, etc., time series of multi-technique combined Epoch Terrestrial Reference Frame (ETRF) and its consistent EOP are to be computed first by introducing the correlation information between each technique-specific reference frame and EOP, adding necessary conditions for datum definition, and so on. 2) In order to model both station non-linear motion and non-linear variation of frame datum, the features of the change of station position and frame datum will be studied and analyzed using the resulting time series of ETRF, and the datum realization of non-linear TRF will be further discussed. 3) Finally, based on the time series of ETRF and its EOP as well as their correlation information, the simultaneous computation model of the non-linear TRF and EOP will be re-established to generate mm-level non-linear TRF and EOP solution.

针对国际地球参考架（ITRF）精度和稳定性有待提高、地球定向参数（EOP）长期解产品与ITRF存在不一致性等问题，IAU专门成立地球自转理论工作组，其核心目标是研究与天球参考架和地球参考架（TRF）相互匹配的地球自转理论及EOP服务产品。本项目拟构建顾及各技术参考架和EOP的相关性以及基准站和参考架基准非线性时变的TRF和EOP同步解算模型：利用VLBI/SLR/GNSS/DORIS解序列及本地连接资料等，施加基准定义约束，引入各技术参考架和EOP相关性信息，快速同步解算历元地球参考架（ETRF）和EOP；采用ETRF时间序列，分析基准站和参考架基准时变性，建立它们各自的非线性变化模型；引入ETRF及其EOP的相关性信息，顾及基准站和参考架基准非线性变化，研究非线性TRF基准定义方法，构建非线性TRF和EOP同步解算模型，常规发布包括基准站季节性信号的自洽毫米级非线性TRF和EOP产品。

实现多技术综合地球参考架TRF和地球定向参数EOP的自洽解算模型精化是一项持久的基础性科研任务，完全自主程序研发并测试解算策略是至关重要且有必要的。指出了最新国际地球参考框架ITRF2014存在的问题，仍无法满足当今毫米级地球运动和形变监测的需要。本项目构建顾及各技术参考架和EOP的相关性以及基准站和参考架基准非线性时变的TRF和EOP同步解算模型。综合利用国际地球参考框架ITRF2014和IVS、ILRS、IGS、IDS的最新成果，快速同步解算历元地球参考架（ETRF）和EOP，对基准站和基准非线性时变特征开展研究，包括台站不连续性自动探测、季节性信号分析、震后形变模型研究等，初步完成一套自研、自编综合解算的方案和程序代码。项目的主要研究内容和结果如下：.（1）以ITRF2014的不连续性文件为参照，搜集其他辅助资料如测站日志、地震记录等预先确定客观存在的跳变发生时刻，采用DIA方法和多元分析方法自动探测台站不连续性，为确保探测结果的准确率、漏判率和误判率，实际数据分析中还需以人工判读手段进行最终不连续性记录的生成。.（2）为避免因缺失数据插补引入误差，利用改进的Lomb–Scargle谱分析方法对中国陆态网260多个台站直接进行季节性信号提取，结合多元加权总体最小二乘迭代解算得到速度场，残余速度的均方根误差平均减少70%以上。.（3）固连在地球表面的各技术观测台站难免会受到地震的影响，探测台站位置时序中存在的震后形变并建立合适的模型，对于参考框架的维持至关重要。在前期研究工作（发表于ASR）的基础上，利用CNO方法直接估计地震弛豫时间，探讨震后形变表征形式的不同组合及优化，解算得到的全球速度场精度优于1mm/a，在N/E/U三个方向的平均均方根误差分别在0.19，0.19和0.33mm/a，且服从正态分布。