Global navigation satellite system (GNSS) remote sensing of the troposphere, called GNSS meteorology, is already a well-established tool in post-processing applications. Real-time GNSS meteorology has been possible since 2013, when the International GNSS Service (IGS) established its real-time service. The reported accuracy of the real-time zenith total delay (ZTD) has not improved significantly over time and usually remains at the level of 5–18 mm, depending on the station and test period studied. Millimeter-level improvements are noticed due to GPS ambiguity resolution, gradient estimation, or multi-GNSS processing. However, neither are these achievements combined in a single processing strategy, nor is the impact of other processing parameters on ZTD accuracy analyzed. Therefore, we discuss these shortcomings in detail and present a comprehensive analysis of the sensitivity of real-time ZTD on processing parameters. First, we identify a so-called common strategy, which combines processing parameters that are identified to be the most popular among published papers on the topic. We question the popular elevation-dependent weighting function and introduce an alternative one. We investigate the impact of selected processing parameters, i.e., PPP functional model, GNSS selection and combination, inter-system weighting, elevation-dependent weighting function, and gradient estimation. We define an advanced strategy dedicated to real-time GNSS meteorology, which is superior to the common one. The a posteriori error of estimated ZTD is reduced by 41%. The accuracy of ZTD estimates with the proposed strategy is improved by 17% with respect to the IGS final products and varies over stations from 5.4 to 10.1 mm. Finally, we confirm the latitude dependency of ZTD accuracy, but also detect its seasonality.

中文翻译：

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在实时天顶对流层估算中考虑GNSS的不同最新进展

对流层的全球导航卫星系统（GNSS）遥感，被称为GNSS气象学，已经是后处理应用中公认的工具。自2013年国际GNSS服务（IGS）建立其实时服务以来，就可以实现实时GNSS气象学。所报告的实时天顶总延迟（ZTD）的准确性并没有随着时间的推移而显着提高，并且通常保持在5-18 mm的水平，具体取决于所研究的测站和测试时间段。由于GPS模糊度分辨率，梯度估计或多GNSS处理，毫米级的改进得到了关注。但是，这些成就既没有组合在单个处理策略中，也没有分析其他处理参数对ZTD精度的影响。因此，我们将详细讨论这些缺点，并对实时ZTD对处理参数的敏感性进行全面分析。首先，我们确定一种所谓的通用策略，该策略结合了处理参数，这些参数被确定是该主题的已发表论文中最受欢迎的。我们质疑流行的基于海拔的加权函数，并介绍一种替代方法。我们调查了所选处理参数（即PPP功能模型，GNSS选择和组合，系统间加权，与海拔相关的加权函数和梯度估计）的影响。我们定义了一种专门用于实时GNSS气象的高级策略，该策略优于普通策略。估计的ZTD的后验误差减少了41％。相对于IGS最终产品，采用拟议策略的ZTD估算精度提高了17％，并且从5.4mm到10.1mm不等。最后，我们确认了ZTD精度的纬度依赖性，还检测了其季节性。