Tropospheric delay is a significant error source in Global Navigation Satellite Systems (GNSS) positioning. Slant Path Delay (SPD) is commonly derived by multiplying Zenith Tropospheric Delay (ZTD) with a mapping function. However, mapping functions, assuming atmospheric isotropy, restrict the accuracy of derived SPDs. To improve the accuracy, a horizontal gradient correction is introduced to account for azimuth-dependent SPD variations, treating the atmosphere as anisotropic. This study uncovers that, amidst atmospheric dynamics and spatiotemporal changes in moisture content, the SPD deviates from that based on traditional isotropy or anisotropy assumption. It innovatively introduces the concept that SPD exhibits non-isotropy with respect to azimuth angles. Hypothesis validation involves assessing SPD accuracy using three mapping functions at five International GNSS Service (IGS) stations, referencing the SPD with the ray-tracing method. It subsequently evaluates the SPD accuracy with horizontal gradient correction based on Vienna Mapping Function 3 (VMF3) estimation. Lastly, the non-isotropic of SPD is analyzed through the ray-tracing method. The results indicate the smallest residual (1.1–82.7 mm) between the SPDs with VMF3 and those with the ray-tracing. However, introducing horizontal gradient correction yields no significant improvement of SPD accuracy. Considering potential decimeter-level differences in SPD due to non-isotropic tropospheric delay across azimuth angles, a precise grasp and summary of these variations is pivotal for accurate tropospheric delay modeling. This finding provides vital support for future high-precision tropospheric delay modeling.

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GNSS对流层延迟非各向同性特征的初步研究

对流层延迟是全球导航卫星系统 (GNSS) 定位的一个重要误差源。倾斜路径延迟 (SPD) 通常是通过将天顶对流层延迟 (ZTD) 与映射函数相乘得出的。然而，假设大气各向同性的映射函数限制了导出的 SPD 的准确性。为了提高精度，引入了水平梯度校正来考虑与方位角相关的 SPD 变化，将大气视为各向异性。这项研究发现，在大气动力学和水分含量的时空变化中，SPD 偏离了基于传统各向同性或各向异性假设的 SPD。它创新性地引入了SPD在方位角方面表现出非各向同性的概念。假设验证涉及使用五个国际 GNSS 服务 (IGS) 站的三个测绘函数来评估 SPD 精度，并使用射线追踪方法参考 SPD。随后，它使用基于维也纳映射函数 3 (VMF3) 估计的水平梯度校正来评估 SPD 精度。最后，通过光线追踪方法分析了SPD的非各向同性。结果表明，采用 VMF3 的 SPD 和采用光线追踪的 SPD 之间的残差最小 (1.1–82.7 mm)。然而，引入水平梯度校正并没有显着提高 SPD 精度。考虑到由于跨方位角的非各向同性对流层延迟而导致 SPD 潜在的分米级差异，精确掌握和总结这些变化对于精确的对流层延迟建模至关重要。这一发现为未来高精度对流层延迟建模提供了重要支持。