Detection of Vibration Signal by Plane Scanning Utilizing Wavefront Sensors

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Authors,

I greatly enjoyed reading your manuscript.  I have some questions about how to actually use your technology.

1. Is this method only usable "one spot at a time"? By that I mean can you monitor different locations simultaneously?  If you can monitor multiple spots, do they have to be contiguously located?  By that I mean can you have a second spot 50 meters away?  Or do you need one system per location?
2. As earthquake motion is typically much less than 1 Hz in frequency, are there any limitations of sensing this type of motion (sampling requirements, instrument drift, etc.)?
3. As a practical matter, would you expect to need to install some kind of reflector for this method to work well?  If you were to try to monitor a spot on the earth with vegetation for example, there would be lots of extraneous motion from wind etc.  How would it actually be used?
4. Is there a motion magnitude issue?  For example, for large ground motion, the phase of the laser light will alias due to its high frequency (and also small wavelength).  For teleseismic events I would expect this not to be much of an issue, however, for strong motion events (near the earthquake) very large amplitude waves will be generated.  Can you talk about this?

Thank you again for a very nice paper!

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This paper presents a novel approach to remote seismic wave detection using wavefront sensors (WFS) and introduces a plane-scanning method for regional vibration measurement. The study effectively leverages the high resolution and array detection capabilities of WFS to enhance laser remote sensing. The experimental validation demonstrates that the proposed method achieves an error margin between 1% and 2%, outperforming traditional laser triangulation methods. I would like to recommend acceptance after the following concerns being addressed:

 

1. The choice of system parameters, such as laser wavelength and spatial resolution, needs further justification. More details on the experimental setup, including calibration and environmental conditions, should be provided for better reproducibility.
2. The reported error range (1%-2%) lacks statistical validation. Including standard deviations, confidence intervals, and repeatability tests would enhance result reliability.
3. The paper compares the proposed method with laser triangulation but does not discuss other relevant methods such as Laser Doppler Vibrometry (LDV) or interferometry. A broader comparison would strengthen the study’s impact.
4. While laser attenuation is mentioned as a limitation, no mitigation strategies are proposed. The authors should discuss potential improvements, such as higher-power lasers or enhanced signal processing.
5. The discussion on related work is insufficient. More recent advancements in wavefront sensor applications for vibration detection should be included.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The purpose of the study presented in the article is not clearly stated and is only partially outlined in the introduction. The main research question or hypothesis is not clearly formulated, which makes it difficult to understand the scientific novelty and significance of the work. The authors propose a method for detecting vibration signals using WFS and planar scanning of target areas, but do not explain why this method was chosen to solve the problem. It is necessary to justify the choice of this method in more detail, compare it to the alternative approaches, such as traditional interferometers, and explain what advantages it provides in the context of remote sensing of seismic waves.

The “Experiment and Results Analysis” section lacks a detailed description of the equipment setup. Although the authors mention some laser parameters (e.g., 120 mW power and 635 nm wavelength), they do not provide full technical specifications of the equipment used, such as the parameters of the telescopes, filters, and other system components. This makes it difficult to reproduce the experiment and assess its accuracy.

In addition, the paper lacks a comparison of the proposed method with alternative approaches such as traditional interferometers. Such a comparison would allow us to evaluate the advantages and disadvantages of the zonal wavefront reconstruction method in terms of accuracy, sensitivity, and applicability in various conditions. How does the Shack Hartmann method perform in the presence of noise and external interference compared to interferometric methods?

Regarding Figure 2, I doubt that the wavefront from the surface under study would be ideal, like the one depicted here on the left. I think it'll be much closer to the one depicted in Figure 3, the complex one, unless the authors used a flat reflecting surface like mirror.

The data presented in tables and graphs (e.g., Table 1, Figures 9–16) are not interpreted in sufficient detail. For example, Table 1 shows laser power data at different distances, but does not explain how this data affects the accuracy of the measurements. Graphs such as Figure 10 show the dependence of phase changes on the amplitude of oscillations, but do not reveal the physical nature of this dependence. Why does the phase change in this way? What physical processes underlie this dependence? In addition, Table 1 is difficult to understand due to the lack of explanations and analysis.

Lastly and probably the most crucial, the article does not discuss how external factors such as temperature, humidity, or wind can affect the measurement results. These parameters can significantly affect the accuracy and stability of wavefront sensors, especially in remote sensing, when the signal is acquired not from several meters in laboratory conditions, but from far away. The authors briefly discuss that “the laser power attenuation in the experiment limited the long-range detection capability, and in the future, it is necessary to consider using high-power lasers to improve the detection distance.” But apart from output power requirements, there would be a lot of factors that would limit the detection. Simply the atmospheric conditions such as turbulence or temperature changes may significantly limit the applicability of the method in real-world conditions.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have addressed most of the comments I raised in the review and improved the quality of the article. Although there are still some points I'd like to clarify first before recommending it for the publication:

Figure 11 caption: "Phase:12.25593334026800rad; (b) Phase:13.4854730003431rad; (c) Phase:15.5999455342686rad; (d) phase:17.704884597561rad". Writing such phase values make no sense, especially without giving the measurement error. Shorten the decimals and give the corresponding error. 

On lines 220 - 224 the authors speak about 6 x 6 microlens array (36 lenses in total). But on the lines 240 - 244 there are 69 microlenses in the array. What's the difference between two? I assume the same SH WFS was used. And the number of microlenses in the array is bigger (for example 11 x 11 or 13 x 13) with only a part of it illuminated? That point needs a clarification. Because later in Figure 15 and on the lines 267 I can see that only 36 microlenses are illuminated and then to 69 again on the lines 302 - 304. It would be insightful if authors provide the whole numbers of microlenses of the wavefront sensor to avoid this confusing point when reading.

Figure 18 is slightly shrunk width wise in the article. The one in the authors' response letter looks better. I suggest replacing it. Same with Figure 20.

And regarding my last comment in the previous review. I asked the authors not to provide the lab conditions, but to speculate on the limitations of the method when it is implemented in real-world conditions. Because, as I said, the environment changes can happen anytime, and they may significantly limit the applicability of the method.

Author Response

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Author Response File: Author Response.docx