Experimental Research on Evaluation of Soil Water Content Using Ground Penetrating Radar and Wavelet Packet-Based Energy Analysis

Round 1

Reviewer 1 Report

The authors conducted a laboratory experiment to estimate soil moisture content using a Ground Penetrating Radar (GPR) and an optimized method called Wavelet Packed-based Energy Index Method. I believe the paper is in a good shape to be published. I have the only minor suggestions:

1. In the list of keywords, I suggest changing those that are already stated in the title. The keywords are a bit too long. For example, “biorthogonal wavelet basis” is better than “construction of biorthogonal wavelet basis”.
2. L69-73: The use of infrared spectra for estimating soil moisture is not so common. On the other hand, there are plenty of studies using microwave spectra (synthetic aperture radar). I suggest searching papers using SAR and soil moisture keywords and then adding a couple of key papers on this subject.
3. L117-123: I suggest moving this part of the manuscript into the Method section.
4. In Figure 5, it seems that there is no change after 15 ns. In order to save space, the range of Y-axis values could be 0-15 ns. Same comment for Figures 9 and 10.
5. Figure 6 shows the saturation point of the energy index whenever soil moisture is higher than 18%. This saturation can be seen in Figure 12 as well. I believe the authors should provide some comments on this.
6. The paper is missing more discussion. Authors go straight from Results to Conclusion. In the Results section, the results are presented, but not discussed in the light of literature (I found only 2 citations). I suggest including at least 2-3 paragraphs at the end of the Results section and adding more citations.
7. Remote Sensing journal uses the abbreviated form of journal names in the Reference section. Please, change them.

Author Response

Dear the Reviewer,

All the authors highly appreciate all the constructive comments and suggestions from the Reviewer. Following are the detailed replies to the reviewers’ comments. In the revised manuscript, all the revisions in the revised version have been highlighted by blue color. The comments from the reviewers have been addressed individually. All the details are listed as follows. More revised parts can be found in the updated version of this manuscript.

Author Response File: Author Response.docx

Reviewer 2 Report

The paper has been significantly improved since the last submission. Now, I think the authors have improved and well explained their work. In my opinion current form of work is suitable for publication. However, I think that some form aspects should be attended by the author prior to be published.

I add some, comments and suggestions which may be useful for the authors.

- pp. 1. Line 21-24 (According to…proposed). In my opinion, the authors should make it explicitly clear what their proposal is in this paper. In this sense, I recommend that the authors include a small piece of the paragraph as appropriate. For instance: ... GPR signals, in this paper a new biorthogonal...

- pp2. line 59-60 (....soil water content in the world…accurate results.) I believe that the authors cannot justify that this is the most used method in the world with just two references. In this sense, I suggest the authors remove the word "in the world" or rephrase as appropriate. In addition, it is not clear there what "simple operation equipment" means, please rephrase this part as appropriate.

- pp2. 61 (…low efficiency, strong destructiveness…). Please rephrase in terms of what you mean when you said "low efficiency" and "strong destructiveness". Rephrase.

- pp2. Line 67 (…less expensive…) “less expensive” compared to what?. Please rephrase.

- pp.3. Line 100-101 (As well…and processing.) This phrase is very strong, not correct, and is not supported. Please rephrase, support with literature and avoid to generalise.

- pp.5 line 207 (…where Z represents an integer.) The domain of Z is missing. In addition, check the Font of the variables throughout the document (e.g. Cambria Match).

- pp.7. line 242-243 (The GPR is used… is inconsistent). Support your assertion with suitable references.

- pp.7. line 243-244 (The Energy can … properties of the medium). Support your assertion with suitable references.

- pp.7. line 244-245 (The WPEI … single-channel signals). Support your assertion with suitable references.

- pp.9. line 316 (Topp and Liu). For clarity, please accompany this quote with its corresponding reference. and I believe that “J.,” it is not necessary.

- pp.12 line 400 (…high energy…). “high energy” compared to what?

- pp.13 line 419 (…is high…). “high” compared to what? What does “high” mean in this context.

- pp16. Line 469 (…demonstrates…). I suggest replace this word with something more appropriate. For example: “These results suggest that…”

Author Response

Dear the Reviewer,

All the authors highly appreciate all the constructive comments and suggestions from the Reviewer. Following are the detailed replies to the reviewers’ comments. In the revised manuscript, all the revisions in the revised version have been highlighted by blue color. The comments from the reviewers have been addressed individually. All the details are listed as follows. More revised parts can be found in the updated version of this manuscript.

PEER REVIEW COMMENTS

The paper has been significantly improved since the last submission. Now, I think the authors have improved and well explained their work. In my opinion current form of work is suitable for publication. However, I think that some form aspects should be attended by the author prior to be published.

Reply: Thanks very much for your constructive and positive comments. The comments from the review sheet have been addressed individually.

I add some, comments and suggestions which may be useful for the authors.

1. pp. 1. Line 21-24 (According to…proposed). In my opinion, the authors should make it explicitly clear what their proposal is in this paper. In this sense, I recommend that the authors include a small piece of the paragraph as appropriate. For instance: ... GPR signals, in this paper a new biorthogonal...

Reply: Thanks very much for your constructive and positive comments.

The sentence has been revised as “According to the time-frequency characteristics of GPR signals, in this paper a new biorthogonal wavelet basis which was highly matched with the GPR waveform was constructed by using the lifting framework of wavelet theory, and then an evaluation method, namely the wavelet packet-based energy analysis (WPEA) method, was proposed.”(Page 1, Lines 21 to 25 of the revised manuscript).

2. pp2. line 59-60 (....soil water content in the world…accurate results.) I believe that the authors cannot justify that this is the most used method in the world with just two references. In this sense, I suggest the authors remove the word "in the world" or rephrase as appropriate. In addition, it is not clear there what "simple operation equipment" means, please rephrase this part as appropriate.

Reply: Thank you very much for your comment.

(1) According to the recommendation of reviewer, the word “in the world” (Page 2, Lines 59 to 60 of the original manuscript) has been removed in the revised manuscript.

(2) The sentence “……because of its simple operation equipment and accurate results” has been revised as “The oven-drying method is a common and standard approach for measuring soil water content, because it can provide more accurate and reliable results than other methods [13, 14].” (Page 2, Lines 57 to 59 of the revised manuscript).

3. pp2. 61 (…low efficiency, strong destructiveness…). Please rephrase in terms of what you mean when you said "low efficiency" and "strong destructiveness". Rephrase.

Reply: Thanks a lot for the constructive comments.

The sentence has been revised as “But it also has some disadvantages, such as long-time testing because the soil sample is subjected to oven drying for 24 h, at 105 ℃, low efficiency for only one sample can be tested at a time, strong destructiveness since the original soil is destroyed for getting one sample [15].”(Page 2, Lines 59 to 62 of the revised manuscript).

4. pp2. Line 67 (…less expensive…) “less expensive” compared to what?. Please rephrase.

Reply: Many thanks for the good comments and advice.

The sentence has been revised as “Compared with the neutron-ray and gamma-ray method, the electrical resistance and capacitance method are less expensive to test the soil moisture content, but both methods are affected by pore distribution, particle size, and salinity [20, 21].” (Page 2, Lines 67 to 69 of the revised manuscript).

5. pp.3. Line 100-101 (As well…and processing.) This phrase is very strong, not correct, and is not supported. Please rephrase, support with literature and avoid to generalise.

Reply: Thanks very much for the valuable comments.

The sentence “As we all know, Fourier transform, just as a frequency-domain analysis method, is not suitable for GPR signals analysis and processing.” (Page 3, Lines 100 and 101 of the original manuscript) has been deleted in the revised manuscript.

6. pp.5 line 207 (…where Z represents an integer.) The domain of Z is missing. In addition, check the Font of the variables throughout the document (e.g. Cambria Match).

Reply: Many thanks for the valuable comments.

Since the parameter k in formula (9) is an integer, from negative infinity to positive infinity. The parameter k belongs to z, and z belongs to an integer in the original manuscript. Therefore, formula (9) is directly rewritten as follows (Page 5, Line 200 of the revised manuscript):

                               (9)

 

7. pp.7. line 242-243 (The GPR is used… is inconsistent). Support your assertion with suitable references.

Reply: Thanks a lot for your good comments.

The sentence “The GPR is used… is inconsistent” (Page 7, Lines 242 and 243 of the original manuscript) has been deleted in the revised manuscript.

8. pp.7. line 243-244 (The Energy can … properties of the medium). Support your assertion with suitable references.

Reply: Thanks a lot for your constructive comments.

The sentence “The Energy can … properties of the medium” (Page 7, Lines 243 and 244 of the original manuscript) has been deleted in the revised manuscript.

9. pp.7. line 244-245 (The WPEI … single-channel signals). Support your assertion with suitable references.

Reply: Many thanks for the good comments.

The sentence “The WPEI … single-channel signals” (Page 7, Lines 244 and 245 of the original manuscript) has been deleted in the revised manuscript.

10. pp.9. line 316 (Topp and Liu). For clarity, please accompany this quote with its corresponding reference. and I believe that “J.,” it is not necessary.

Reply: Thanks a lot for the constructive comments.

The sentence has been revised as “According to the formulas of Topp and Liu, the relative dielectric constant and electrical conductivity of the soil with different water content is calculated in this paper [68, 69].” (Page 9, Line 299 and 300 of the revised manuscript).

The lists of Reference [68, 69] are added in the revised manuscript (Page 24, Lines 772 to 775), which are also shown in the follows.

[68] Topp, G. C. Electromagnetic determination of soil water content: Measurements in coaxial transmission lines. Water Resour. Res. 1980, 16(3), 574-582.

[69] Liu, J. Methods of detection on moisture of railway subgrage by using the ground penetrating radar. PhD thesis, China University of Mining & Technology, Beijing, China. 2015.

11. pp.12 line 400 (…high energy…). “high energy” compared to what?

Reply: Thanks very much for your constructive comments.

The sentence has been revised as “Figure 10 shows that the direct wave signals have a large amplitude and high energy compared to the electromagnetic wave reflection signals, which seriously interfere with the reflection signals of the model boxes and reduce the quality and resolution of GPR images.” (Page 14, Lines 425 to 428 of the revised manuscript).

12. pp.13 line 419 (…is high…). “high” compared to what? What does “high” mean in this context.

Reply: Many thanks for the valuable comments and advice.

The sentence has been revised as “The results show that the resolution of the GPR images in Figure 11 is high compared with the resolution in Figure 10 when the direct wave and noise are removed and the reflected signals of the model boxes can be displayed more clearly and intuitively.” (Page 16, Lines 449 to 451 of the revised manuscript).

13. pp16. Line 469 (…demonstrates…). I suggest replace this word with something more appropriate. For example: “These results suggest that…”

Reply: Thanks very much for the valuable comments.

According to the reviewer’s suggestion, the sentence has been revised as “These results suggest that the WPEI of the GPR signals continue to increase as the water contents of clay increase and the correspondence are highly correlated.” (Page 17, Lines 488 and 489 of the revised manuscript).

Author Response File: Author Response.docx

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Im not a native english speaker but it is clear the text has certain flaws just starting from the abstract: Line 17-18 "First of all, taking soils samples with water content in THE model box as an example, THE GPR forward simulation software was used to perform..." when then reader does not know still what model box or simulation software the authors refer  
But in general in my opinion the text is well elaborated a has a nice flow even if sometimes is unnecessarily repetitive (I think could be well reduced to half number of pages keeping the important content).   
The theoretical background looks good even if I confess I havent gone into the formulas in detail.
The part regarding the simulation fails a bit in my opinion when authors claim they are trying to simulate clay. It looks to me their model is a simple homogeneous material with different permittivities. If a real attempt to simulate clay under different mositure levels were made then would be very interesting for the readers to know some info how they constructed the model (Debye, Havriliak-Negami....) 
The part regarding the experiments is really great, very nice setup and data with a lot of potential for analysis.
In my opinion when I think the paper fails really is when demonstrating how well the method performs. From physics point of view is clear that we will have more energy in the reflected signal with more contrast in permittivity. A simple analysis of the energy of the reflected signals seems  a nicer template for comparison than daubechies. I say this mainly because two things: 1) amplitude analysis is one of the most used methods in GPR to calculate permitivity values and 2) daubechies in the example fail even to follow the increased energy profile with moisture (something that is practically visible with naked eye comparing the radargrams in Figure 9). 
The title claims "determination of soil water content" but what the authors present seems at most a valuable method to differenciate between different moisture levels.  

Reviewer 2 Report

This study aims to determine soil water contents using a new energy index based on wavelet packet transform (EIWPT) method. This method was used to calculate the energy indices of the GPR signals from clayey soils with different moisture contents.

Unfortunately, I cannot recommend publication of this paper in the Remote Sensing journal just because there is no remote sensing in the manuscript. The GPR and EIWPT methods provide point-based soil moisture estimations, similar to the field soil sampling for volumetric soil moisture estimations. In other words, they are not spatial data, which is the basic principle of remote sensing. I believe there are more appropriated journals to submit it (e.g., Sensors, Journal of Applied Geophysics, and Journal of Hydrology, which are cited several times by the authors).

Reviewer 3 Report

Although the study is interesting, the relevance, novelty, intentionality, and usability of this study is not reflected enough in the document. The methods proposed in the work, are raised in a very superficial way, they are not duly justified and it is not a straightforward task to follow the author's argument, with which it is difficult to identify both the novelty and the usefulness. I think that the authors have to make an effort at this point to try to show the new aspects that are included in their proposal and why the real need to carry out this new approach. This not only in the introduction but also when the formulations are explained.

 

The selection of the case studies selected to verify the effectiveness of the proposal made are not duly justified. I think that it should be better justified what is the usefulness of identifying clay samples with different water content in a sand box and no other stratum, e.g. pavement or better express what is the intention of the authors with these targets. Similarly, the selection of the frequency used in the study and the depths of the samples are not properly justified, making it difficult to adequately explore the effectiveness of the proposed method. Furthermore, it is difficult to verify how this method is better than previous processes for this type of analysis, as the authors argue.

 

In reference to the body of the work, quantity and diversity of the used works in the papers could be improved. The paper is correctly written and the mathematical treatment should be improved. However, formal aspects such as the definition of the all variables used in the document should be improved. The analysis of the results is presented in superficial way and I consider a more deep analysis of the data and images is required. The justification and the uses of the information are not properly used in the document. Regarding the literature review that supports the document, I consider that the information has been treated in a superficial way which loses its value. One of the main problems in this regard is that the author tends to generalize and many of the arguments are not properly supported. The use of summary tables and synoptically schemes which allow the reader to orientate is missing. The figures and diagram are not adequately explained within the document. This is especially critical in the absence of a diagram to guide the reader through the steps of the proposed method. Since at this point the reader could better identify what is new.

 

About the rest of the document, individual analysis of the results in this document should be improved. In some cases this seems like a simple comment made in a superficial manner. The general approach of the paper is a bit blurring and the general analysis about the used data, the proposed method and how it what selected at each step of the proposed process in this work, and the relationship between them should be improved.

 

Novelty, intentionality, relevance and usability are not reflected in the abstract. Furthermore, the abstract has many vague sentences that need to be improved. The selection of the methodology is not properly justified and explained. These in aspects such as the selection of methods, antennas, number of tests, characteristics of the targets, results, among others. This aspect is very important in validation (part that is missing or not easily to be found) of the obtained results. There is not clear why the paper required a section of results, discussions and conclusions. It is not clear why the document required a poor results, discussions and conclusions sections. In my opinion, it would be more effective if the discussion section was divided between the results section and the conclusions section. This with the aim of making these two stronger. The conclusions are poor and do not highlight the findings of the work and their relevance.

 

I add some, comments and suggestions which may be useful for the authors.

 

1. 1. line 10-11 (Therefore...foundations) Why GPR and no other destructive method? Please rephrase

 

1. 1. Line 11- 4 (The time-frequency… personnel). Why wavelet and no other processing techniques? Please rephrase

 

1. 1. line 16-14 (According to...constructed). Where was it constructed? Rephrase.

 

1. 1. line 16-17 (A new...proposed) I suggest that these sentence can be merged with the previous one or rearranged in order to get a stronger sentence. Improve.

 

1. 1. line 17-19 (First... method.) This sentence is not clear this looks like if the study attempt to verified the feasibility of the EIWPT instead the feasibility of uses of EIWPT to....

Please rephrase.

 

- In addition, what does mean GPR forward simulation software?

 

1. 1. line 21 (...conduct four repetitive experiments....) What does "four repetitive experiments" mean? Rephrase.

 

pp.1. 38 (...the physical...) Some examples with references of physical properties are required here.

 

pp.1. line 39 (...mechanical properties...) Some examples of mechanical properties that you are referring are required here.

 

1. 1, line 40 (...engineering properties...) What does "engineering properties" mean? Explain.

 

Entire document. Check the missing space among the word and references in entire document (e.g. pp.1 line 43 "...etc[3,4].".

 

Please, support your assertion in the following sentences:

 

pp2. line 54-55 (The oven...common approach…) Support your assertion with references different than 7-9.

 

pp2. line 54-55 (...of its simple...results.) Support your assertion

 

pp2. Line 56-58 (But it…detection data)

 

pp2. Line 59-60 (but its response…is narrow)

 

pp2. Line 60-61 (…quickly determine the soil water content on site…)

 

pp2. Line 61 (the operation… complicated…)

 

pp2. Line 62 (may have… human health) Support your assertion and some examples of human health impact as consequence of the uses of this technique are required.

 

pp.2. line 63 (…but they….soil,…) Support about this method is required. In addition a brief explanation about why these are destructive methods is missing.

 

pp.2. line 71 (…employs…) I suggest replace by “captures” or similar word.

 

pp.2. line 71 (…waves to distinguish…) I suggest to change this part for something more appropriate, for example “...waves that potentially may allow to distinguish...”

 

pp.2. line 74 (…soil material,…etc.) Put one or more references at the end of each example. For instance, “soil material [reference]”.

 

pp.2. line 78 (…estimate…content,…) support your assertion.

 

pp.2. line 78-79 (…but the…to determine,…) support your assertion.

 

pp.2. line 80-81 (The spectrum analysis method…) Why this method as an example and no others. Explain.

 

pp.2. line 81-82 (…can convert…signal,…) support your assertion.

 

pp.2. line 83-84 (…its depth are difficult to determine…) support your assertion and explain briefly.

 

pp2. Line 87 (…multiphase and variability of soil…) support your assertion.

 

pp.2. line 87-91 (For long time…and processing.) There are several methods in order to analise the GPR signals. Rephrase, justify and support your assertion.

 

pp.3. line 100 (on the experience…personnel.) support your assertion.

 

pp.3. line 101-106 (Moreover…processing.) Support and justify your assertion and some examples are required.

 

pp.3. line 109 (…biorthogonal wavelet…) Brief explanation about biorthogonal wavelet is required.

 

pp.3. line 110 (…energy index based…) Brief description about this index is required.

 

pp.3. line 118 (…superiority…) Consider changing the word “superiority” to a more appropriate word. Rephrase.

 

3. 3. Between line 137-138. I suggest here to put a figure with the schematic architecture of the proposal with a brief introduction of the steps that make it up.

 

pp.3. line 139 (…better extract…) Comparing with? Rehprase

 

pp.3. line 145 (…decomposition… are) The meaning of the "decomposition end" and "reconstruction end" are missing. Explain and support.

 

Please, check in entire document that all the variables involved in the formulations are explained into the text. For instance, in equation 1, z and q are missing.

 

pp.4. line 168-169 (…Haar…bank with…) A brief explanation is needed on the meaning and relevance of the Haaretz wavelet filter. In addition, a justification of its uses is required.

 

pp.4. line 175 (…the following relationship…) How do you find these relationships? A short explanation about it is required.

 

pp.5. line 177 (…scale filter.. a new…) Briefly explain the relevance of this scale filter.

 

pp.5. line 191 (…approximate…component D.) Explain and support the meaning of the component A and D.

 

Figure 1. The figure is not explained in depth in the text. A brief explanation about the meaning and relevance of this figure, as well as its components, is required.

 

pp.5. line 197 (and… expression is…) Provide the source of this formulation.

 

In the same manner, the relevance of this step in the entire proposed process is missing. Explain the uses and relevance of this section.

 

pp.6. line 202 (…the EIWPT employed…) There is not any justification about the uses of this method. explain, support and justify it.

 

pp.6. line 207 (…energy…obtained.) Why you want to obtain it?

 

pp.6. line 208 (…packet…GPR.) There is not any justification about the uses of this method. explain, support and justify it.

 

pp.6. line 210 (…sampling theorem…) support with references.

 

pp.6. line 213 Verify that the variable s has not been used before. In the same way, establish the ranges of the variables used in the entire document.

 

pp.6. line 212 (…Nyquist frequency…) A brief explanation about Nyquist frequency is required.

 

Please verify that all equations that are not proposed by you have their corresponding reference to support them. For example pp6. line 215.

 

6. 6. Line 225-227. Explain why this part is needed for the proposed approach. In addition, check that all the variables have been explained into the text.

 

pp.6. line 238 (…by the control unit. ) Signals are received for the antennas, not for the control unit. In addition there are several configurations for these antennas (e.g. monostatic, bistatic, among others). In this sense, although the GPR principle is the same, its analysis sometimes requires some considerations. Please, explain briefly the type of system that you are considering in your approach.

 

pp.7. line 249 (The propagation…complicated.) Vague and not exact sentence, please improve it.

 

pp7. Line 259 (…was dry sand…) Why dry sand? Explain.

 

pp7. Line 261 (…was 1600 MHz…) What was the criteria for the selection of the antenna? Why is this antenna appropriate for this type of study? Explain

 

pp.7. line 265 (GPR …software…) Which software. Please provide the reference.

 

pp.7. line 265 (…adapted to perform…) This mean that you have modified the code or only you have used it?

 

Pp7. Line 266 (…cavity model…) Explain briefly what is the relationship between a cavity model with soil water content or why you need a cavity model in this study.

 

Figure 4. Define epsilon into the text.

 

pp.11. line 343 (…signal… by direct waves…) Improve the explanation of the figures.

 

Figure 8 and Figure 9. Check the location of the red box.

 

pp.12 line 360-361 (image…is high…) What does mean “that the image resolution of the GPR signal in Figure 9 is high,”. Improve the sentence.

 

pp.12 line 361-362 (…the outline of…is clearly visible.) Highlight the outline of the model box in the figures.

 

1. 13 line 378-379 (Among them,…by analogy.) and pp.14 line 393-394 (Among them,…and others are analogized.) and pp.15 line 429-430 (Among them,…and others are analogized.) The analysis is vague and superficial. Improve.

 

pp.15 line 412 (this demonstrates that…) why this demonstrate that? Explain and support your assertion.

 

pp.15 line 415 (…slightly different…) what does “slightly different” mean?

 

pp.15 line 419. (“superiority”) replace for a suitable word.

 

pp 15 line 422-424 (Many analyses… GPR signals.) Support your assertion.

 

pp 15 line 424 (…db6..) Define and explain db6 wavelet basis.

 

1. 16 line 437-438 (Figure 12… the law.) It is not clear how the author demonstrate this. Improve your explanation.