【作者】 张杰；

【导师】 李斐；

【作者基本信息】 武汉大学 ， 大地测量学与测量工程， 2014， 博士

【摘要】 以GPS (Global Positioning system)为代表的现代空间定位技术手段的蓬勃发展和广泛应用,近20年来积累了大量的宝贵原始观测数据,也为大地测量和地球物理等地学研究领域开辟了广阔的前景。高精度和高可靠性的GPS数据处理结果是地学研究的基础,海潮负荷位移改正对提高GPS估计精度已经得到了广泛的共识,也为GPS坐标时间序列研究中剥离海潮负荷效应影响提供了有效途径,同时利用GPS坐标时间序列分析可以检验海潮负荷模型的精度和适应性。因此在GPS精密测量中研究海潮负荷效应对大地测量和地球物理学研究获取准确的几何和物理信息具有重要的理论意义和参考价值。本文系统地阐述了GPS精密测量中海潮负荷效应在国内外的发展现状和趋势,分析了海潮负荷影响GPS精密测量的各个关键环节,着重研究了不同海潮负荷模型位移改正对GPS坐标精密定位的修正效果,建立了海潮负荷位移和天顶对流层延迟(ZTD)估计精度的变化特征关系,深入分析了未模型化的海潮负荷位移传播到GPS高程时间序列的混叠信号的周期变化特征。主要研究内容和成果如下：(1)系统研究了海洋潮汐和海潮负荷的理论基础,介绍了海洋潮汐产生的引潮位理论以及海洋潮汐的调和展开,给出了海洋潮汐和海潮负荷分析方法的详细表达式。(2)系统研究了非差精密单点定位所涉及的基本理论,包括各种GPS时间系统及相互转化关系、各种GPS坐标系统及相互转化关系、基本观测方程和参数估计模型,针对数据处理过程中的误差项,着重分析了非差精密单点定位主要误差源和改正模型及方法。(3)利用全球海潮模型FES2004的M2分潮波深入研究了我国海域的海潮空间特征分布,得出我国海域的M2分潮振幅主要分布为：较小振幅的南海区域,较大振幅的渤海、黄海和东海区域以及大陆近海岸的异常区域。在此研究基础上,给出了我国陆海全区域的海潮负荷位移三维坐标分量,海潮负荷的垂向位移分量为水平位移分量的3～4倍,同时在沿海陆地和近海海洋区域海潮位移变化较大。通过7种全球海潮模型分析了不同海潮负荷位移在我国不同区域范围内的影响差异,结果显示近海区域的不同海潮负荷位移的均方根误差较大,间接证明了全球海潮模型在我国近海区域精度具有较低的精度。(4)针对我国及周边地区的13个IGS站,分别采用全球海潮模型和经近海海潮模型修正的全球海潮模型计算及分析了各测站的海潮负荷位移,并利用GPS实测数据研究了海潮负荷对单天解和短时段周期解的精度影响。实验结果表明局部近海海潮模型和全球海潮模型相应区域的精度相当,计算的海潮负荷位移未引起明显的差异。对于GPS单天解精密定位结果,从整体上各海潮负荷位移对测站坐标没有影响,但是在局部沿海地区测站的垂向坐标存在差异；对于GPS短周期精密定位,海潮负荷位移改正对我国沿海地区测站的精度能够提高2.5mm。(5)深入分析了利用映射函数和水平梯度模型进行GPS天顶对流层延迟估计的精度,结果显示选用GMF映射函数会比NMF映射函数从整体上提高了ZTD估计精度。在低高度角和气象变化剧烈条件下,施加水平梯度改正也能提高ZTD估计精度。研究了ZTD与海潮负荷位移的关系,通过解算结果确定了在我国及周边地区的IGS站的海潮负荷位移垂向分量与ZTD变化具有显著的线性对应关系,同时二者的比例因子在2-5范围内变化。为了满足GPS气象学应用PWV值优于1mm的精度要求,特别是在沿海地区必须要顾及海潮负荷效应的作用对ZTD估计偏差的影响。(6)系统研究了GPS高程时间序列的长周期混叠信号传播机制,确定了未建模的海潮负荷位移造成我国及周边地区8个测站的GPS高程时间序列长周期混叠信号周期和振幅分布特征,发现混叠信号主要集中于约14天、半年和周年周期,未建模的海潮负荷垂向位移引起GPS高程时间序列的混叠信号振幅能达到海潮负荷高程分量振幅的12%,而未建模的海潮负荷水平位移引起GPS高程时间序列的混叠信号振幅最大达到海潮负荷水平分量振幅的100%,同时基于未建模海潮负荷三维分量相对于未建模海潮负荷高程分量的GPS高程时间序列的频谱振幅和周期发生了明显变化,分析表明即使水平负荷位移量值很小,但是对于GPS高程时间序列混叠周期信号频谱特征解释具有不可忽视的作用。提出了通过GPS高程时间序列的频谱分析,利用特定频率的振幅峰值评估不同海潮模型的相对精度特征,为海潮负荷模型定量分析提供了简明的评估手段。更多还原

【Abstract】 With the vigorous development and wide application of modern space positioning technology represented by GPS (Global Positioning System), a large amount of valuable raw data has been accumulated in the past20years, which opens up the broad prospects for geoscience’s research such as geodesy and geophysics. High precision and high reliability of GPS data processing result is regarded as a basis for geoscience’s research, ocean tide loading displacement corrections to improve the estimation accuracy of GPS has been adopted widely, it not only provides a effective means to separate the effect of ocean tide loading from GPS coordinate time series, but also can test the accuracy and adaptability of ocean tide model using GPS coordinate time series, so analyzing ocean tide loading effect in GPS precision measurement hold the important theoretical meaning and reference value in better service for geodetic and geophysical research.In this paper, the development trend of ocean loading effect in GPS precision measurement is analyzed and summarized, the different ocean tide loading models are focused on, the relationship between ocean tide loading displacement and the zenith tropospheric delay (ZTD) variation is established, and the spurious long period signal character in GPS height time series is further investigated, which is caused by unmodeled ocean tide loading displacement. The main contents and achievements are as follows:(1) A brief overview of basic theory for modeling ocean tide and ocean tide loading displacement is given. The tide-raising potential and its harmonic expansion are studied, and then the expression analysis methods to ocean tides and ocean tide loading are derivate in detail.(2) The measurement models of zero-difference PPP(Precise Point Positioning) is introduced, including GPS time systems and the transformation between them, GPS coordinate systems and the transformation between them, code pseudo range measurement, phase pseudo range measurement and parameter estimation models. At last the error sources of zero-difference PPP are analyzed and the correction models and methods are summarized.(3) The spatial distribution characteristics in China Sea area is obtained by the M2constituent of the global ocean tide model of FES2004. The result reflects small amplitude region in the South China Sea, the larger amplitude region in the Bohai Sea, the Yellow Sea and the East China Sea, amplitude anomaly region near the coastal areas. On the basis of this study, the ocean tide loading displacements are computed across China, the magnitude of the vertical displacement are3-4times as large as that of the horizontal displacements, meanwhile ocean tidal loading displacement change is great in the coastal and offshore areas.7kinds of global ocean tide models are chosen to analyze the effects of different ocean tide loading displacement in different regions of China, the results show that the root mean square of different ocean tide loading displacement is larger in the offshore area, that indirectly testifies that global ocean tide models have a lower accuracy in the offshore region in China.(4) Using the global ocean tide model and local ocean tide model in China Seas, the ocean tide loading displacements are calculated and analyzed for13IGS stations in China and the surrounding areas. GPS daily and sub-daily solutions are investigated when ocean tide loading displacements are modeled and then not modeled. According to the comparisons, the accuracy of local ocean tide model and those from global ocean tide mode is in the same level, between which ocean tide loading displacements are identified. For GPS daily solution, on the whole the ocean tide loading displacements have no effect on the station coordinate, but have influence on the vertical coordinates of the coastal stations; for GPS sub-daily solutions, ocean tide loading displacement correction can improve2.5mm accuracy on the coastal stations in China.(5) GPS-derived ZTD estimates are researched when the mapping function and the horizontal gradient are taken into account. The results show that GMF is better than NMF, which increases ZTD estimation precision. While horizontal gradient can also improve the accuracy of ZTD estimation, especially under the conditions of low cut-off elevation angle and weather dramatic changes. The effect of ocean tide loading vertical displacement on GPS-derived ZTD estimates is investigated in China and the surrounding areas, the linear relation between ocean tide loading vertical displacement and ZTD is found, the scaling factor is in the range of2-5for a7°cut-off elevation angle. In order to meet the requirements of GPS meteorology application that precipitable water vapor (PWV) is better than1mm, ocean loading effects must be taken into when estimating ZTD from GPS data, especially in the coastal area.(6) The aliasing signal propagation mechanism in GPS height time series is systematically studied. Spurious long period signal characters are investigated by analyzing GPS time series at8stations in China and surrounding areas at which the ocean tide loading displacement is not modeled. It is found that spurious long period signals rang in period from fortnight to one year, mainly focus on fortnight, semiannual and annual periods. It is shown that the unmodeled height component periodic ground displacement can propagate to GPS height signal with admittance of12%, whereas the horizontal admittance maximum reaches a maximum of100%. At the same time the spurious long period signals caused by unmodeled three-dimensional component are obviously different from that caused by unmodeled height component. It is reflected that the horizontal load displacement values are very small, but those can not be ignored for spectrum characteristics interpretation. At last a concise evaluation method is provided for accuracy assessment of ocean tide loading models through the peak amplitude of specific frequency in GPS time series.更多还原