Coastal High-Temporal Sea-Surface Altimetry Using the Posterior Error Estimations of Ionosphere-Free PPP and Information Fusion for Multi-GNSS Retrievals

Round 1

Reviewer 1 Report

Since my research field is SNR-based GNSS-MR, I don't know the details of positioning very well and have some doubts about Section 2.2.

 

Line 263, ” Taking sin? as an independent variable, Equation (8) can then be written as”. Do you mean the detrending method was used to remove the term NIF+T? According to your statement, I have no way of knowing what specific operation I have gone through to get the (L_IF ) ̃.

 

Line 263-269. “Since the multiple effects derived from GNSS PEs are far larger than the random noise of ??1 −??2, the noise component can be ignored”. Do you mean the PE series plotted in Figure 6 is the (L_IF ) ̃ series? How can the PE be obtained? What’s the difference between your method and other GNSS-MR methods using carrier-phase observations?

 

Table 3 and Figure 12. Table 3 shows the retrieval points from carrier-phase observations are significantly greater than these from SNR. But in Figure 12, the retrieval points look almost the same amount. Can you give the explanation?

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Sea level change is an important parameter for oceanographic studies and it is well documented in the literature that GNSS reflectometry can provide meaningful contributions in this regard complementing observations from traditional tide gauge sensors. This study focused on a) establishment of a posteriori error-based GNSS-IR sea sea‑surface altimetry method, b) serious data quality control, and c) modelling of high-temporal sea level retrievals. These results are interesting and contribute to the future study as well. Based on all of the above, I recommend publication of the paper after a minor revision.

 

There are the following several questions regarding the manuscript.

 

1. The paper proposed a new sea level retrieval approach, but I think that the specific processing strategies for the detrended GNSS posteriori error (PE) arcs seem to be not enough clear in Section 2.2. We suggest to add a summaried table to help the readers understand it.

 

2. Line 152: “Both SC02 … EarthScope Plate Boundary Observatory (PBO, http://earthscope.org)”, need some references, e.g.,

 

Larson, K.M.; Nievinski, F.G. GPS snow sensing: results from the EarthScope Plate Boundary Observatory. GPS Solut 2013, 17, 41-52. doi:https://doi.org/10.1007/s10291-012-0259-7.

 

In addition, this URL for PBO (http://earthscope.org) seems no longer possible. Thus, I was able to access GNSS data via the alternative link https://www.unavco.org/data/gps-gnss/gps-gnss.html. Please check.

 

3. Figure 2: Please add a North Arrow and mark the source of this picture.

 

Table 3 and Table 4: we suggest to indicate a time interval for the number of retrieval points, i.e., the number of retrievals per day.

 

4. Figure 16:

In Figure 16b, the red line represents the residuals between the PE-based sea level retrievals and tide gauge, and both black dotted lines determine a distribution interval for most residuals. However, this interval is rough. We suggest to describe the residuals in the intervals of [μ-σ,μ+σ], [μ-2σ,μ+2σ], and [μ-3σ,μ+3σ], respectively.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Dear author,

Thank you very much for your paper “Coastal high-temporal sea-surface altimetry using the posterior error estimations of ionosphere-free PPP and information fusion for multi-GNSS retrievals”.

I find your work very interesting and, in fact, we should use the phase residuals for multipath as well as the SNR. Both are influenced by this effect. A combination of both should lead to an even more stable solution.

You describe your procedure very well, your presentation of the results is also very clear and straight forward. In principle, I have only minor comments on some typos and grammar:

1.       Use present tense in the Abstract

2.       Line 38: what is “rising altimetry”? The interest on altimetry which is rising?

3.       Line 41 one blank to much

4.       Line 61: what does RHCP and LHCP mean? Can it be skipped?

5.       Line 90: “the in of the reflector height”

6.       Skip Figure 3

7.       Line 204: here elevation is ment not azimuth

8.       Line 219: both sides

9.       Line 250: call it speed of light

10.   Line 262: a be is missing: can be simplified

11.   Line 375 “can be significantly improved”

Best regards.

Author Response

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Reviewer 4 Report

Dear Authors,

Review of the paper: “Coastal high-temporal sea surface altimetry using the posteriori error estimations of ionosphere-free PPP and information fusion for multi-GNSS retrievals”

 

In this paper a very interesting and important theme, which deals with proposal of a new sea-surface altimetry method, is discussed.

This topic is of great importance for a large number of activities such as climate change, navigation safety at sea, coastal projects and etc.

I have carefully read the paper. The construction of the paper is good and correct, but I have one small and one big remark.

 The suggestions bellow have the purpose to contribute with the authors.

 My general comments and suggestions are as follows:

1.      The title of chapter 4 is “Conclusions and Discussion”. I suggest that this chapter be separated into two chapters, as is customary in scientific practice: “4. Discussion” and “5. Conclusions”. At the same time, the “Discussion” should be much more extensive.

2.      My main objection is based on the fact that the authors use a small series of measured data to assess the quality and accuracy of the applied method for determining sea-level height. So, in my opinion, the paper is not original scientific work.

 

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 4 Report

Dear Authors,

I think the manuscript has been sufficiently improved so my recommendation is to publish it.

Author Response

Thank you very much for your approval to our manuscript.