10:45 AM - 12:15 PM
[SGD02-P13] Development of GNSS tropospheric delay correction system at MRI (3rd report)
Keywords:GNSS, Tropospheric Delay, Numerical Weather Model
Introduction
We started developing a GNSS tropospheric delay correction system in 2021, and have been improving the system. Last improvement is the implementation of the ray-bending, which improved the delay correction slightly (Okuyama et al., 2022). We then partially introduced the effect of spherical Earth to further improve the correction.
Data and Method
In general, GNSS tropospheric delay correction is accomplished by giving a-priori delay model as zenith path delay and mapping function, then estimating the deviation from the model. Our system replaces well-known VMF1 (Boehm et al., 2006) with the model calculated from JMA Meso-Analysis GPV data (2017-2019: Horizontal grid size = 5km, Number of layers = 50, Time interval = 3hrs). To introduce the effect of spherical Earth, we revised the path length for the integration and incidence angle on each layer. Let dh be the thickness of given atmospheric layer and e be the elevation angle of the ray, path length through the layer dL is given by dLflat=dh/sin(e) assuming flat Earth. On spherical Earth, dLsphere is slightly smaller than dLflat because the layer is spherical shell. Similarly, incidence angle isphere is smaller than iflat=pi/2-e. We introduced the effect of spherical Earth by replacing dLflat and iflat with dLsphere and isphere.
Result
To validate our model, we compared the mapping function at e=10[deg] with that of VMF1. We found that the difference became significantly smaller, from ~0.2 excess to ~0.04. This is because the path length for the integration is now much closer to the real path length. We also applied our delay model to actual observation data and found that the repeatability is improved slightly.
Further improvement
We have not introduced the effect of spherical Earth on the calculation of piercing point of the ray path with each atmospheric layer. Better correction is expected by implementing this feature.
Acknowledgement
We used RINEX data and F5 solution by Geospatial Information Authority of Japan for the calculation of station coordinates. We thank Dr. Tsuyoshi Watanabe for his advice about the configuration of GNSS analysis.
We started developing a GNSS tropospheric delay correction system in 2021, and have been improving the system. Last improvement is the implementation of the ray-bending, which improved the delay correction slightly (Okuyama et al., 2022). We then partially introduced the effect of spherical Earth to further improve the correction.
Data and Method
In general, GNSS tropospheric delay correction is accomplished by giving a-priori delay model as zenith path delay and mapping function, then estimating the deviation from the model. Our system replaces well-known VMF1 (Boehm et al., 2006) with the model calculated from JMA Meso-Analysis GPV data (2017-2019: Horizontal grid size = 5km, Number of layers = 50, Time interval = 3hrs). To introduce the effect of spherical Earth, we revised the path length for the integration and incidence angle on each layer. Let dh be the thickness of given atmospheric layer and e be the elevation angle of the ray, path length through the layer dL is given by dLflat=dh/sin(e) assuming flat Earth. On spherical Earth, dLsphere is slightly smaller than dLflat because the layer is spherical shell. Similarly, incidence angle isphere is smaller than iflat=pi/2-e. We introduced the effect of spherical Earth by replacing dLflat and iflat with dLsphere and isphere.
Result
To validate our model, we compared the mapping function at e=10[deg] with that of VMF1. We found that the difference became significantly smaller, from ~0.2 excess to ~0.04. This is because the path length for the integration is now much closer to the real path length. We also applied our delay model to actual observation data and found that the repeatability is improved slightly.
Further improvement
We have not introduced the effect of spherical Earth on the calculation of piercing point of the ray path with each atmospheric layer. Better correction is expected by implementing this feature.
Acknowledgement
We used RINEX data and F5 solution by Geospatial Information Authority of Japan for the calculation of station coordinates. We thank Dr. Tsuyoshi Watanabe for his advice about the configuration of GNSS analysis.