There is limited discussion on the impact of SSR corrections based on different ACs on RT ZTD accuracy. In this study, RT-PPP based on multiple ACs is used to estimate the positioning performance and ZTD accuracy of SSR products based on different ACs. GNSS from 8 IGMAS stations is increased from 355 in 2023 to 14 in 2024. WHU-SSR has a higher accuracy of RT-PPP derived ZTD with an RMSE of 6.06 mm and a perfect availability with an integrity rate of 89 %.

In this paper, we propose an improved pixel-based water vapor tomography model, which uses layered optimal polynomial functions by adaptive training for water vapor retrieval. Under different scenarios, tomography results show that the new model outperforms the traditional one by reducing the root-mean-square error (RMSE), and this improvement is more pronounced, at 5.88 % in voxels without the penetration of GNSS rays. The improved model also has advantages in more convenient expression.

This paper proposes an optimal tropospheric tomography approach with the support of an auxiliary area, which has the ability to use the signals crossing out from the top boundary of the tomographic area. Additionally, the top height of the tomography body is determined based on the average water vapour distribution derived from the COSMIC data. The compared result reveals the superiority of the proposed method when compared to the conventional method.

This paper captures the signature of heavy rainfall events using the 2-d-/4-d water vapour information derived from GNSS measurement in Hong Kong. The paper first analyzed the relationship between the two-dimensional (2-d) precipitable water vapour (PWV) and rainfall. And then, the four-dimensional (4-d) variations of atmospheric water vapour derived from the GNSS tomographic technique are discussed, especially in the vertical irection. Finally, some interesting results are found and presented.