Review Reports

Round 1

Reviewer 1 Report

GNSS reflection technology is widely used. In this work, taking wheat as an example, the height fluctuation of ground vegetation is analyzed in detail, which is of great significance and hopes to be applied in production as soon as possible.

The format of individual references is not uniform, and it is suggested to modify.

With the Global Navigation Satellite System interferometric reflectometry (GNSS-IR) technique, surface environmental information can be detected. This authors use observations of the GNSS-IR to investigate wheat lodging and obtain some valuable results.

 

This topic is relevant in field of the Journal. This work use special observation data series. The work show very good results, which can be applied to wheat lodging warning in the future.

 

In my opinion, the technique isn’t introduced firstly by the authors. However, with these observation series, the author made a comprehensive analysis and got some meaningful results. This is the greatest contribution of this work.

 

The structure of the paper can be combined with this research and analysis to get corresponding conclusions.

 

 

Author Response

Dear reviewer,

Thanks four your comments and suggestions. We have carefully unified the format of the references you mentioned. We deeply appreciate your consideration of our manuscript, and we look forward to receiving comments from you.

Sincerely.

 

Reviewer 2 Report

please find my comments in the attached pdf. The study is interesting and the article well written and understandable. However, I have a strong concern regarding the weighting you use (references?) and also the measure you chose to compare the results (coerrelation coeff is probably not the best choice here). I would suggest to use the dynamic time warping for instance, to compare features here. A high R is not obligatory a good indicator in statistics. Here, visually, the curves seem close to each other though. Could you please discuss more about the models in the next iteration? What about the reliability since it seems to fit well in most cases. Many thanks for having let me reviewed you article, I am looking forward for the revision.

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Monitoring wheat growth is an original and promising GNSS application, and the paper is interesting in that sense.  However, in my opinion, it lacks rigor, the description of the methodology should be refined, and the general English usage should be improved.  Some specific comments below.

 

Line 135: “previously been modeled”: a reference should be provided here.

Section 2.1: please illustrate these concepts with a figure showing an example of SNR pattern over a satellite pass.

Equation 8: describe N  (number of satellites?)

Eq (9) and Eq(10): these should be ratio, but the equations do not show ratios.  To be explained or corrected.

Line 207: what is “fourth layer”.  To be clarified.

Line 213: the “normalized amplitude” must be defined. 

Line 214: why is the “0.78” value selected? 

Eq (11) this segmentation seems arbitrary.  Why adding exactly a wavelength in some cases?  Why making a special case for L1?  The paper does not provide convincing theoretical ground for this. It seems to me that the authors have chosen Eq (11) to fit the observed data.  How general are these equations?

Eq (11): showing a picture illustrating those segments would help.

Eq (12): the symbol “N” was already used in Eq (11), but with a different definition.  This is misleading.  Please use different symbols for different quantities.

Eq (13): why does the GDD have an index “k”.  How can GDD depend on the constellation “k”?

Line 240-256: for each date (e.g. April 25), also mention the DOY for better readability.

Line 279: “GDD model simulations of each frequency band and each GNSS system”.  Explain how the GDD model depends on the frequency band and constellation.

Line 299: “the retrieval height of L1 and B1-2 are obviously better than these of L2/L5 and B2b/B3”.  Why is this “obvious”?   What is the reason for that?  To be explained.

Line 356: “Obviously, most of the residuals are concentrated within ±0.15 m while those from the L5/G2/E5b/B2b frequency band are slightly larger, with a variation of ±0.20 m. The errors based on L1/G1/E1/B1-2 frequency, are slightly worse than those of the other frequency”.  This seems contradictory.  It is first said that the error in L5/G2 is larger, and then that the error is worse in L1/G1…  To be clarified.

Line 378: ”Compared with the retrievals of single frequency, the results of the proposed method perform better”.  How can this be concluded from Fig 16, which only shows the combined retrieval?

Line 410: “this research aims to verify the relationship between normalized amplitude and WWC”.  WWC is never mentioned or defined in the paper.  This sentence must be deleted from the conclusion, or supported by the text.

Line 423: “Therefore, it was possible to monitor the wheat lodging and give early warning”.  The paper does not present any result about lodging, so this also should be removed from the conclusion.

 

General remarks:

Equation and Table numbering should be reviewed, e.g. on line 141, Eq(2) should be Eq(3).  Table 1 appears twice, on line 263, Fig 6 should be Fig 5, etc…

Many sentences are grammatically incorrect and the paper needs proofreading.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 4 Report

This paper presents a solid experimental study on monitoring of wheat height using multi-GNSS reflected signals. The results validated with ground-truth measurement look promising. I recommend the paper to be published after addressing several minor issues as below.

In Figure 12-15, could you please explain why the retrieval errors change sign after 60 days? Can this be resolved by introducing a phase-wrapping approach?

Page 2, Line 78: upper case for kg/m2

Page9, Line 261: ‘single’ to ‘Single’

Page 11, Line 312: ‘segmented processing’ to ‘Segmented processing’’

Page9, Line 274: ‘Multi-frequency’ to ‘multi-frequency’

Page11, Line 274: ‘In-situ’ to ‘in-situ’

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

my concerns were adressed. There are still a few typos, please check carefully once the paper is accepted.