A comparison of GPS, VLBI and model estimates of ocean tide loading displacements
A comparison of GPS, VLBI and model estimates of ocean tide loading displacements
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DOI：
10.1007/s00190-006-0118-9
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发表时间：
2006-12
影响因子：
4.4
通讯作者：
I. Thomas;Matt A. King;P. Clarke
中科院分区：
文献类型：
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作者：
I. Thomas;Matt A. King;P. Clarke
近年来，人们利用全球定位系统（GPS）和甚长基线干涉测量（VLBI）测量了海洋潮汐载荷位移（OTLD）。本研究通过与 VLBI 测量值和数值海潮模型得出的估计值进行比较，评估 OTLD 的 GPS 测量值的准确性。对 25 个站点中每一个站点约 11 年的 GPS 数据进行了每日精确点定位 (PPP) 分析，这些站点之前根据来自同一地点的 VLBI 站点的数据进行了 OTLD 估计。在可能的情况下，歧义被固定为整数值。由此产生的 OTLD 每日估计值（八个主要日潮汐频率和半日潮汐频率）相结合，得出每个站点 OTLD 的 GPS 测量值。将 OTLD 的 3D GPS 和 VLBI 测量值与五种现代海潮模型（CSR4.0、FES2004、GOT00.2、NAO99b 和 TPXO6.2）计算的估计值（通过与格林函数卷积）进行比较。 GPS/模型协议与 VLBI/模型协议类似。在重要的径向方向上，八个潮汐成分中的七个的 GPS/模型失配小于 VLBI/模型失配； K2 成分除外。将 GPS 载波相位模糊度固定为整数值导致 GPS/模型一致性略有改善。从统计上看，OTLD 的 GPS 和 VLBI 测量与模型值的拟合之间没有显着差异。同样，整套 GPS 或 VLBI 估计值与五组模型导出值的拟合差异也无法通过统计显着性来确定。因此得出的结论是，总体而言，我们无法区分 OTLD 的 GPS 和 VLBI 测量，并且在全球范围内，现有的海潮模型在这些技术的当前测量噪声范围内是准确的。
In recent years, ocean tide loading displacements (OTLD) have been measured using the Global Positioning System (GPS) and Very Long Baseline Interferometry (VLBI). This study assesses the accuracy of GPS measurements of OTLD by comparison with VLBI measurements and estimates derived from numerical ocean tide models. A daily precise point positioning (PPP) analysis was carried out on ∼11 years of GPS data for each of 25 sites that have previous OTLD estimates based on data from co-located VLBI sites. Ambiguities were fixed to integer values where possible. The resulting daily estimates of OTLD, at eight principal diurnal and semi-diurnal tidal frequencies, were combined to give GPS measurements of OTLD at each site. The 3D GPS and VLBI measurements of OTLD were compared with estimates computed (by convolution with Green’s functions) from five modern ocean tide models (CSR4.0, FES2004, GOT00.2, NAO99b and TPXO6.2). The GPS/model agreement is shown to be similar to the VLBI/model agreement. In the important radial direction, the GPS/model misfit is shown to be smaller than the VLBI/model misfit for seven of the eight tidal constituents; the exception being the K2 constituent. Fixing of GPS carrier-phase ambiguities to integer values resulted in a marginal improvement to the GPS/model agreement. Statistically, it is shown there is no significance to the difference between the fit of the GPS and VLBI measurements of OTLD to modelled values. Equally, differences in fit of either the complete set of GPS or VLBI estimates to the five sets of model-derived values cannot be identified with statistical significance. It is thus concluded that, overall, we cannot distinguish between GPS and VLBI measurements of OTLD, and that at the global scale, present ocean tide models are accurate to within the current measurement noise of these techniques.