GNSS provide invaluable positioning data for countless applications, from everyday navigation to scientific research. Tropospheric delays, caused by the refractive properties of the atmosphere, significantly impact the accuracy of GNSS positioning. The standard practice of multiplying Zenith Tropospheric Delay (ZTD) by a Mapping Function (MF) to derive SPD operates under an assumption of atmospheric isotropy, limiting precision in GNSS applications.
On a recently published study in the journal Satellite Navigation, researchers from Shandong University of Science and Technology introduces a novel concept that SPDs are non-isotropic with respect to azimuth angles, departing from traditional isotropic and anisotropic assumptions. They utilized three different mapping functions and conducted evaluations at five International GNSS Service (IGS) stations, employing the ray-tracing method as a benchmark. The study compared SPD accuracy using Vienna Mapping Function 3 (VMF3) and found the smallest residual between VMF3-derived SPDs and ray-traced SPDs. Surprisingly, introducing a horizontal gradient correction for azimuth-dependent SPD variations showed no significant improvement in accuracy.
