An Integrated GNSS/MEMS Accelerometer System for Dynamic Structural Response Monitoring under Thunder Loading

Round 1

Reviewer 1 Report

The manuscript implements a system for dynamic responses of the Great Wall of China, with the thunder loading using an integrated vibration monitoring system that includes a Global Navigation Satellite System (GNSS) receiver and 3-axis MEMS accelerometers. The low/high natural frequencies of the bricks of the Great Wall are extracted by image denoising through Variational Mode Decomposition (VMD) with subsequent Power Spectral Density (PSD) analysis using both GNSS and accelerometer data. The effectiveness of the proposed integrated processing scheme is validated through field monitoring data. The authors claim that thunderstorms can cause the Great Wall to vibrate with a maximum displacement of 14.3 cm. From my perspective, the work done in this manuscript is worthy and interesting but still needs additional efforts to project the severity of the effects as detected by the present procedure.

Specific Comments:

1)      The authors explained the denoising algorithm with VMD, power spectral density method to discriminate the natural frequency and thunderstorm-induced frequency deviations for specific events at a countable number of sites. However, the reason behind the selection of those particular events and sites is not clarified.

2)      The uncertainty level of the biases from one instrument to the other is unknown. Are those instruments calibrated with a common bias.

3)      A strong literature on similar works done for any DAMs, huge construction sites or walls is missing in the literature as well as in the discussion. I suppose the thunderstorm effects could also be harmful for any huge dams or high-rise towers and similar elevated structures. The authors are suggested to include any such works on the current problem that are done in the past.

4)      The natural frequency and thunderstorm-induced frequency are mentioned by the authors. However, the threshold level of frequencies at a site for causing possible deformation is unknown. Maybe, more studies are needed to support the objective with a meaningful advisory to the decision makers about the classified frequency levels are severity.

5)      Moreover, the conclusion looks weak, it just repeats the results, rather than extracting the conclusions and future directions.

6)      While reading the manuscript, however, I encounter a few English corrections as follows, which I am sure the authors could rectify in the subsequent version.

 i.   Line 22 Power Spectral Density (PSD) => PSD as it is already defined at line 17

 ii.   Line 48 Figure 1 is not cited inside the text. Is this deformation of the wall happened due to any specific thunderstorm loading?

iii.   Line 101 characteris tics => characteristics

  iv.   Line 130 power spectral density => PSD

  v.   Line 316 What is the rationale behind selecting only two days to obtain an average natural frequency for a site? The authors should support this with literature.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

The paper investigates the interesting phenomena − the dynamic response of the Great Wall of China on a thunderstorm impact. The special monitoring system and processing methodology were developed by the authors and presented in the manuscript. The topic of the paper is interesting for the appropriate specialists. However, I would like to recommend the moderate revision of the manuscript due to the following aspects:

1) The authors should clarify the main goal of the paper. What kind of research they would like to present  - the new type of a monitoring system and its characteristics or results of investigation of the dynamic response of the Great Wall on a thunderstorm load?

If the second task is solving then much more GNSS/MEMS data collected under different thunderstorm events should be analyzed in order to really investigate the Great Wall response parameters. Only two events and limited set of data are considered here. In my opinion the manuscript in its present form just demonstrates that the Great Wall shows detectable response to some thunderstorm events. However, it does not provide an answer on the question: what events are really dangerous for the Great Wall stability because they excite vibrations which might coincide with resonant frequencies of the construction?

The comparison of the obtained results with similar investigations which have already done by other research groups is very important.

If authors would like to present a new monitoring system they have to clearly demonstrate its sensitivity to thunderstorm events of different scale and effectiveness for the Great Wall deformation monitoring.

2) What GNSS-processing software is used for displacements monitoring? What accuracy level can be achieved (mm- or cm-level displacements can be detected)?

3) The Table 2 can be reduced till the time span 19:00 - 22:00. The remaining part of the table can be explained by a few sentences in the text.

4) I did not find the Table 3 anywhere in the manuscript!

5) The last paragraph of the conclusion (Lines 338-342) do not related with the present study. It contains just general and obvious words. I recommend to remove or significantly update it.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The manuscript might be accepted in its present form.