Kinematic ZTD Estimation from Train-Borne Single-Frequency GNSS: Validation and Assimilation
Round 1
Reviewer 1 Report
The idea of using train-borne SF GNSS ZTD to improve the numerical weather prediction is very interesting and promising since we have a large amount of kinematic platforms in daily life. This manuscript provides an initial validation of idea which mainly focused on the assessment of train-borne SF GNSS ZTD estimations. The manuscript is generally well written and organized, but there are still some concerns need to be addressed as below.
1. The data assimilation analysis is not too weak and not convincing. Acceptance rate cannot represent the benefit of the GNSS-derived ZTD to data assimilation. I would suggest the authors comparing the WRF-ZTD after the assimilation with GNSS ZTD at some independent geodetic stations to check the improvements compared to WRF-ZTD without ZTD assimilation.
2. The settings in different schemes were not well designed. You should use the same mapping function and a-priori ZHD model in different schemes, or we cannot distinguish that which factors made the PPP results different.
3. L290: how about the spatial resolution of the height coordinates in the database? Are they geodetic height or height above the mean sea level (MSL)? If they are height above the MSL, how did you convert them to geodetic height that used in GNSS data processing? How about the introduced errors in this conversion? How did you constrain the height in PPP? i.e., the a-priori height error.
4. Exchange the order of Figure 3 and Figure4 because Figure 4 is mentioned before Figure 3 in the texts.
5. Font size is too small in some Figures
6. L433: the possible reason?
7. L438: any reference to support this statement?
8. Why no SGAMP result for CS2?
9. Why CSRS-PPP is worst in CS1 but best in CS2?
10. Table 8: no PPPW-HC result?
Author Response
Please see the attachment
Author Response File: 
Author Response.docx
Reviewer 2 Report
First of all, I would like to express my deep respect to all the co-authors for this excellent study related to GNSSZTD. The topic of this study is interesting and the authors have presented the results with sufficient analyses. The present study will provide further better understating on the impact of GNSS ZTD observations on NWP systems. Thus I recommend the paper published in the Remote Sensing Journal.
Author Response
We would like to express our gratitude for this very positive feedback on our work.
We are pleased to know that our work is valued and hope to push forward this topic in the future, taking into account all lessons learned from this initial study.
Round 2
Reviewer 1 Report
The authors have addressed all my concerns. I recommend the acceptance of the manuscript after the revision of the following two minor problems.
1. Table 7 and Table 10: show the difference with EPOSA rather than the absolute values
2. L312: Please provide reference for the geoid undulation accuracy of about 2 centimeters
Author Response
We are glad that all major points could be addressed.
We have updated the tables for the ZTD difference to the EPOSA stations and provided the reference for the Geoid accuracy as requested.
