Understanding Ocean Acoustics by Eigenray Analysis
Round 1
Reviewer 1 Report
I do not see a lot of sense in the paper in its current form. It presents the tutorial regarding specific section of underwater sound and could be a chapter in one of underwater acoustic textbook. There are a lot of books in underwater acoustic with good chapters describing ray analysis application for sound field prediction. I prefer book Urick, R.J., Principles of underwater sound.
I think that the presented material could be good illustration to the real acoustic case. The paper can demonstrate application of the ray theory for prediction of the field of an airgun array briefly mentioned in the end of the paper. The authors can write good tutorial for seismic surveying using airgun systems. This tutorial can be of this this paper with the paper [7].
I also want to mention that the section regarding particle velocity can be extended. There are a lot of publications about vector sensor application in underwater acoustics. Review of vector sensors and its application for the seismic survey can be included to the improved paper.
Author Response
This paper is about underwater acoustics not on seismics
Agree on including
Urick, ,R, J. Principles of Underwater sound, 3rd ed. New York: McGraw_Hill. Reprinted by Peninsula Publishing, CA,1996
Reviewer 2 Report
Paper is easy to read and will be nice companion for potential users of this ray-based program.
A minor comments:
Au are no doubt aware of other publications involving the same PlaneRay results as shown here (e.g., I found one in IEEE). That is fine as this paper goes into more tutorial detail. However, why not include here a more simple benchmark example that new users can easily dublicate? For example, propagation in sloping seabed as first done with PE by Jensen and Kuperman. The simple sloping bottom would be easy for new users to duplicate along with simple penetrable seabed.
Author Response
Au are no doubt aware of other publications involving the same PlaneRay results as shown here (e.g., I found one in IEEE). That is fine as this paper goes into more tutorial detail. However, why not include here a more simple benchmark example that new users can easily dublicate? For example, propagation in sloping seabed as first done with PE by Jensen and Kuperman. The simple sloping bottom would be easy for new users to duplicate along with simple penetrable seabed.
Agree and done by referring a paper reporting exactly the reviewer proposed
1 Hovem, J. M Korakas A. Modelling Low Frequency Loss in the Oceans. Proceedings of the 1st Underwater Acoustics Conference and Exhibition 23 to 28. June 2013 Corfu Island Greece , pp 1517-1522
Reviewer 3 Report
General comments
The manuscript concerns the use of ray modelling and in particular eigenray analysis to obtain increased knowledge and understanding of underwater acoustic propagation. After careful analysis, this reviewer considers that the manuscript can be recommended for publication, but the authors could enhance the content of the manuscript. Such recommendation follows from the assumption that the manuscript successfully manages to present in a coherent manner different theoretical and computational aspects of ray tracing, which are of extreme relevance for signal modeling and for the processing of experimental data.
The authors could also include what this model differs from others and what makes it better, or not!!! (Time consumption, complexity, etc…).
This reviewer also recommends the manuscript to be revised for the elimination of typos.
The list of references should be improved, since from 10 references presented 5 are from the authors.
A few remarks are presented in the following:
Remarks
Line 18 to 35: the Introduction could be improved with a brief State of Art. This reviewer thinks that this section has a lot of duplication of the Abstract.
Line 47: this reviewer considers the number of alternative ray models considered to be surprisingly reduced, namely by mentioning only Bellhop and PlaneRay. A review of the Ocean Acoustics Library allows to identify much more (TRIMAIN, EigenRay, TRACEO, etc.).
Line 68: is the sentence “This section may be divided by subheadings.” necessary?
Line 94 and Figure 1: The text mention 5m but in the caption of the Figure 1 is written 25m.
Line 98: In the caption of Figure 1, The authors could end with “… for northern waters, on the left.”
Line 111: The sentence “A plot of range versus initial angle is shown in Figure 2." is confusing. Consider, for instance, a ray trajectory (r; z) calculated for an initial angle of 30º. A figure showing the initial angle over r would exhibit a straight line. The same would happen for other angles different from 30º. Thus, how is Figure 2 obtained?
- The method of ray history for the calculation of eigenrays certainly has its merit. Yet it is unclear what are the advantages over other methods. The authors should clarify this in the manuscript.
Line 131: Class 13 in Table 1, the initial direction is positive not negative, right?
Eq(2) is different from Eq(13) in reference 5.
Eq(3) is different from Eq(15) in reference 5. The ratio c0/c should be c/c0.
Line 179 and 180: source depth 5m and receiver depth 100m, in the caption these values are different and observing Figure 5, the values are 25m and 150m, respectively.
Line 212 to 215: The authors must clarify this paragraph. What theories? References?
It is unclear how Eq(5) was obtained. Are they frequency dependent? What is the dependence?
Particle velocity is a vector, but the nominal particle velocity introduced with Eq(6) is an scalar. The authors must clarify this, since particle velocity is an issue with a growing interest, as the authors refer in the manuscript.
It is unclear how Eq(7) was obtained.
Section 4.4 Could be improved with comparisons between other ray models’ outputs.
Although a good comparison between experimental results and PlaneRay model is obtained, the authors could improve with comparisons with other ray models.
Line 316: The Appedix A
The validation of the Ray Theory could be included in the body of the manuscript and not on the Appendix. The authors could explore this topic.
Typos
Line 34: “... to obtain increase knowledge ..." should be “... to obtain increased knowledge ..."
Line 65: “MATAB" should be “MATLAB".
Line 66: “... and to understand the code" should be “... and to understand the code."
Line 85: “Raytrcing and Ray Histry" should be “Raytracing and Ray
History".
Line 197: “Figure 6 show a cross…” should be “Figure 6 shows a cross…”
Line 198: “… Figure 6 are for a hard and soft bottom, respectively.” should be “… Figure 6 are for a hard and soft bottom, left and right respectively.”
Line 224: “Modlling" should be “Modelling”
Line 235: “...introduce a nominal particle as..." should be “...introduce a nominal particle velocity as...".
Author Response
Line 18 to 35: and Line 47
Added a general reference to he Ocean Acoustics Library as a source for update on State of the art
Line 68: is the sentence “This section may be divided by subheadings.” necessary?
No and deleted
Line 94 and Figure 1: The text mention 5m but in the caption of the Figure 1 is written 25m.
Corrected to 25 m
Line 98: In the caption of Figure 1, The authors could end with “… for northern waters, on the left.”
Agree and added
Line 111: and later remarks
Agree that this section is confusing. Have now interchanged sections 3.3 and 3.4 such the equations for intensity and TL come in a more logical positions and and a justification and need fro the sorting routine.
Also added in text:.
The main problem with using ray history for calculating eigenrays are the calculation of the incremental range increase for a given change in initial ray angle. A plot of the trajectory of for a single initial angle is a, in general, discontinues function not suited for interpolation. The sorted classes will have relatively continuous range-angle relations and therefore be amendable to interpolation. The calculation of the derivativeis performed using the sorted and interpolated values to ensure high accuracy of the estimates is a unique feature of PlaneRay
Line 131: Class 13 in Table 1, the initial direction is positive not negative, right?
Agree and fixed
Eq(2) is different from Eq(13) in reference 5.
Agree and fixed
Eq(3) is different from Eq(15) in reference 5. The ratio c0/c should be c/c0.
Agree and fixed
Line 179 and 180: source depth 5m and receiver depth 100m, in the caption these values are different and observing Figure 5, the values are 25m and 150m, respectively.
Agree and corrected
Line 212 to 215: The authors must clarify this paragraph. What theories? References?
Inserted reference to Brekhovski h and Lysanov
It is unclear how Eq(5) was obtained. Are they frequency dependent? What is the dependence?
Added:
The eigenrays are plane waves therefore having the property that the particle velocity is the sound pressure divided by the specific acoustic impedance. The particle velocity is proportional to the gradient of sound pressure and therefore the horizontal and vertical components of particle velocities are found by
Particle velocity is a vector, but the nominal particle velocity introduced with Eq(6) is an scalar. The authors must clarify this, since particle velocity is an issue with a growing interest, as the authors refer in the manuscript.
It is unclear how Eq(7) was obtained
Added:
There is no proof for this expression, but it postulates that the transmission loss is purely geometric and is composed of two parts.
.
Section 4.4 Could be improved with comparisons between other ray models’ outputs.
Although a good comparison between experimental results and PlaneRay model is obtained, the authors could improve with comparisons with other ray models.
Line 316: The Appendix
The validation of the Ray Theory could be included in the body of the manuscript and not on the Appendix. The authors could explore this topic.
This has been done r by Hovem and Koroakas in 2013 comparing PlaneRay with OASES and RAMS .( I had forgotten this paper) The reference is now in the main Text and the appendix is removed
Typos
All typos corrected
Round 2
Reviewer 1 Report
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