Satellite product combination has been a major effort for the International GNSS Service Analysis Center Coordinator to improve the robustness of orbits, clocks and biases over original AC-specific contributions. While the orbit and clock combinations have been well documented, combining phase biases is more of a challenge since they have to be aligned with the clocks precisely to preserve the exactitude of integer ambiguities in precise point positioning (PPP). In the case of dual-frequency signals, frequency-specific phase biases are first translated into an ionosphere-free form to agree with the IGS satellite clocks, and they can then be integrated as integer clocks to facilitate a joint combination. However, regarding multi-frequency phase biases, forming their ionosphere-free counterparts would be cumbersome as they are linearly dependent. We therefore propose a concept of “frequency-specific integer clock” where all third-frequency phase biases are integrated individually with satellite clocks to enable an efficient frequency-wise combination. The resultant combined product will ensure all-frequency PPP ambiguity resolution over any frequency choices and observable combinations. Our combination test based on the GPS/Galileo satellite products from four IGS-ACs in 2020 showed that the mean phase clock/bias consistencies among ACs for all third-frequency signals (i.e., GPS L5, Galileo E6 and E5b) were as high as 10 ps, and the ambiguity fixing rates were all around 95%. Both quantities reached the same levels as those for the baseline frequencies (i.e., GPS L1/L2 and Galileo E1/E5a). The combined products outperformed AC-specific products since outlier contributions were excluded in the combination.

卫星产品组合是国际 GNSS 服务分析中心协调员的一项重大工作，旨在提高轨道、时钟和偏差的稳健性，超过原始 AC 特定贡献。虽然轨道和时钟组合已得到充分记录，但组合相位偏差更具挑战性，因为它们必须与时钟精确对齐，以保持精确点定位（PPP）中整数模糊度的准确性。在双频信号的情况下，频率特定的相位偏差首先被转换为无电离层形式以与IGS卫星时钟一致，然后它们可以被集成为整数时钟以促进联合组合。然而，对于多频率相位偏差，形成其无电离层对应物将很麻烦，因为它们是线性相关的。因此，我们提出了“频率特定整数时钟”的概念，其中所有第三频率相位偏差都与卫星时钟单独集成，以实现有效的频率组合。由此产生的组合产品将确保对任何频率选择和可观察组合进行全频率 PPP 模糊度解析。我们基于 2020 年四台 IGS-AC 的 GPS/Galileo 卫星产品进行的组合测试表明，所有三频信号（即 GPS L5、Galileo E6 和 E5b）AC 之间的平均相位时钟/偏置一致性高达10 ps，歧义修复率均在 95% 左右。这两个数量都达到了与基线频率（即 GPS L1/L2 和 Galileo E1/E5a）相同的水平。组合产品的性能优于特定于 AC 的产品，因为组合中排除了异常贡献。