Estimation of Coarse Root System Diameter Based on Ground-Penetrating Radar Forward Modeling

Round 1

Reviewer 1 Report

This is a review report of the manuscript titled "Estimation of Coarse Root System Diameter Based on Ground Penetrating Radar Forward Modeling."

The manuscript presents a new method for estimating the diameter of coarse roots using Ground Penetrating Radar (GPR) operating at a frequency of 900 MHz. The method is developed to address the limitations of traditional approaches that may harm plants and their growing environment. The manuscript provides a clear outline of the steps involved in establishing the estimation model and validating its practical applicability.

The manuscript begins by describing the creation of a simulation model that accurately replicates natural root systems. This model serves as the basis for establishing the root diameter estimation model using GPR scanning results. The authors also investigate the influence of soil and root relative permittivity on the estimation model, developing a method that allows for the determination of the model under varying soil and root conditions.

To assess the effectiveness of the diameter estimation model, the researchers test it on roots with different growth orientations by simulating various root orientations. This analysis confirms the model's applicability to roots in different orientations.

The practical applicability of the proposed method is then validated through field experiments. The results demonstrate that the root diameter estimation model, which involves extracting waveform parameters' pixel distance (Δp) from the 900 MHz scanning results, consistently provides accurate estimations.

The manuscript highlights that the proposed method is effective for estimating the diameter of coarse roots with a minimum diameter of 2 cm and a relative permittivity greater than 5. It proves to be applicable to roots in any orientation and various soil environments.

The significance of accurately estimating the coarse root diameter is emphasized, as it offers valuable experimental data for promoting healthy tree growth. Additionally, it contributes to the study of coarse root ecology.

In summary, the manuscript introduces a nondestructive method for estimating the diameter of coarse roots using GPR. The method is thoroughly validated through simulations and field experiments, demonstrating its effectiveness across various root and soil conditions.

 

Author Response

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Reviewer 2 Report

This study proposes a new non-destructive method for estimating underground root diameter using ground penetrating radar (GPR) at 900 MHz. Through simulation of the root system and analysis of signal parameters obtained from scanning, a root diameter estimation model was developed and tested under different soil conditions and growth orientations. The GPR system consists of a control unit, an antenna and a display unit. By emitting electromagnetic waves into the soil and detecting received reflections, the GPR generates a radargram showing reflective features at different depths. In the case of roots, the radiation will detect the upper and lower apex of the root system, providing information about its location and structure. A total of 240 combinations of root and soil permittivity were examined, with each group containing data from 335 scans of seven roots with diameters between 0.01 m and 0.07 m. Root analysis by simulation indicated a definite positive linear relationship between root diameter and the distance in pixels between the vertices of two hyperbolas obtained from it. The results of the scans were used to develop models for estimating root diameter based on the distance in pixels. Different combinations of root and soil permittivity were considered. The propagation speed of electromagnetic waves through roots is related to the relative permittivity of the roots. The accuracy of the estimation models depends on the knowledge of the relative permittivity of the roots and soil. The validity of the models was verified by comparing estimates of root diameters with actual values. The results confirm the effectiveness of the method, offering a new opportunity to obtain reliable root diameter estimates in complex situations and providing useful information for healthy plant growth and the study of root ecology. The article is well organized and provides a comprehensive abstract describing the objectives of the work and the methodologies used. The topic is covered in detail, referring to the provinces analyzed and the time frame considered. The text is clear, well structured and relevant to the estimation of root system diameter based on Ground Penetrating Radar. A good percentage of recent literature references within the last five years is cited. The work is scientifically sound and the experimental design is adequate to test the proposed hypotheses. The figures, diagrams, tables, and images correctly present the data analyzed and are easy to interpret. The conclusions are consistent with the evidence and arguments presented. Overall, the study is clear, comprehensive and relevant to the field of experimentation considered. The objectives of the work and the method/approach used are addressed effectively, showing good logical coherence between the different parts of the work. The text is grammatically correct, easy to understand and pleasant to read. The results obtained are clearly presented and commented on. All in all, the article, in addition to having significant bibliographic/dissemination value, has many elements of scientific interest. The article is consistent with the purpose of the journal.

Author Response

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Reviewer 3 Report

Please find here comments on your interesting article titled “Estimation of coarse root system diameter based on ground penetrating radar forward modeling”, where you present your experimental results on estimating root diameter from ground penetrating radar. I will focus on the statistical methods and presentation of results.

In general, I found the article well-written and clear, but I have some concerns about some of the presentation of the results. Below, I suggest some changes that I believe should improve the presentation of the article.

The figure captions are mostly lacking in description, and I present a few examples here, where extra detail should be added so that the reader can understand what each diagram represents:

-          Figure 2: There seem to be three separate figures here, but it is not clear what they show. Please can you give a lot more detail to explain what each plot shows?

-          Figure 3: What do the blue and red areas represent? The axis labels are too small to read.

-          Figure 4: There are lots of labels that are not included in the text (R0 etc.) These should be explained in the figure caption.

-          Figure 5: the x- and y-axes should be labelled in the diagram.

-          Figure 6: More explanation is required. E.g., what are the letters A, B and C?

In terms of presenting your results on page 12, you note that the results showed a “good” estimation effect (line 426). Can you please add to the text how you are defining “good”, i.e., how is this assessed?

I think that Figure 15 might not be the best way to present your results here. It is not clear which black circle each red circle is associated with, so that the reader cannot tell from this diagram how well the method is performing. I think that a scatterplot might be a better choice here, since you could then show more clearly how the observations and predictions relate to each other. (You could colour the points by diameter or permittivity to retain this information in the diagram.)

In terms of the 14 models over different soil relative permittivity values, I think that looking into mixed effects models might be a good idea for future work, since you could then consider whether a single model would be appropriate or whether separate models are really required for each permittivity value. However, I will not suggest doing this for the current paper, as I think the methods that you have used get the point across.

In line 620, you refer to Models 2 and 3, but it is not clear what these refer to. Can this be updated, so that the reader can identify these models, please?

Below, I have added some additional minor comments:

-          Line 54: “significant” does not make sense here. I think this should maybe be “indicator”.

-          Line 58-60: The finding that root system diameter increases with age seems obvious. Could you add a bit more detail on how exactly the authors found that this increased with age (e.g., linear/nonlinear).

-          Line 87: The word “the” should be removed.

-          Line 91: I think that “volume water” should be “water volume”.

-          Line 299: Can you please add the units of measurement for permittivity and water content?

-          Line 454: “were almost a straight line” is not clear. Do you mean that the values were all very similar? I think the wording can be improved here.

-          Line 558 to 559: I do not understand what “reference significance” means here. Could the wording please be changed to make this sentence clearer?

Aside from the minor comments that I have made in my comments to the authors, I found the article clearly written, and I have no concerns about the quality of English language use.

Author Response

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Author Response File: Author Response.docx