Latest Advances in Common Signal Processing of Pulsed Thermography for Enhanced Detectability: A Review
Round 1
Reviewer 1 Report
The review is focused on the latest advances in signal processing of optical thermography. The authors describe the basic concept of infrared thermography and non-destructive testing at first. Then they focused on recent advances in signal processing techniques.
The review is easy to read and contains the most important information about IRT NDT algorithms. In its current form, the review is interesting predominantly for students and scholars with limited knowledge of active thermography. I believe this review could be a big help for them. Introduced techniques are well known and were described in many other reviews (for example Recent Advances in Active Infrared Thermography for Non-Destructive Testing of Aerospace Components, Optically and non-optically excited thermography for composites: A review). That limits the usability of the review for professionals and researchers working in the field of active thermography.
The review is very good but the title is misleading. Please change the title or add some new (not that common) signal processing techniques. I would strongly suggest authors add the newest processing techniques for active thermography. Recently I saw many interesting new methods as methods based on virtual wave-based image processing, thermal effusivity method, super-resolution laser thermography, dynamic thermal tomography, time power transformation method, structured heating, and its evaluation. I believe there are many more and reviews like that would be interesting to a broader audience. The article also didn’t contain much information about the latest advances in laser thermography.
Some notes:
The review contains excessive citations of some authors. E.g., Ranjit Shrestha - the total number is 17 plus 3 which are badly cited (Ranjit instead of Shrestha). The same applies to Wontae Kim (22). Those authors are most cited in your review and I believe the number of those citations is too high.
The part about Lock-in thermography looks a bit obsolete. You describe the 4 bucket method as a standard signal processing technique. This method was the first one used but it seems to me that now the standard lock-in method is more commonly used as described in O. Breitenstein, W. Warta, and M. Langenkamp, Lock-in thermography, vol. 10. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010.
Chapter 4.1. is written in a different style than the rest. Articles of some authors are presented but no results are discussed. It is not obvious what was the result of the research. Other chapters are fine (for example 4.2).
Chapter Trends is very short. The review is intended to be about the latest advances so it would be nice to know what authors expect to be popular in the future.
Line 59 area. Dot is missing
Line 63 halogen instead of Halogen
Line 100 I would add a decimal. -273.15 instead of -273
Line 119 SWIR and LWIR range... could you find some source? Many different publications use different numbers. This is a review article so it would be nice to have it backed up with a source.
Line 162 I believe that the general schematic should contain a synchronization unit.
Line 171 Photographic instead of photographic
Line 175 I would be very careful with this statement. There are many low-power flash lamp and also many high-power halogen lamps. Maybe add usually.
Line 180 The table is a bit misleading. Lock-in thermography can be used with other excitation sources not just with halogen lamps. You stated the most common sources. Also Beneficial instead of beneficial
Line 203 have been instead of have bene
Line 232 within 0.2 °C. Could you please specify the source?
Line 256 between 2 to 15. Do you mean ms?
Line 267 and 268 equations. Reconsider to put them in equation form.
Line 275 Figure 4 has poor quality
Line 304 Equation to equation form
Line 351 The picture is confusing. What is gimbal control? I would expect a picture composed of laser, laser scanning head, sync box, IR camera, and PC.
Line 359 For some readers it may be confusing to read about one-dimensional discrete Fourier transform and next about FFT. You didn’t even explain that it is Fast Fourier Transform. I believe for most readers it won’t be a problem but for clarity please explain a little bit more.
Line 433 The image has very bad quality.
Line 445 the optimal degree of n is from 6 to 9. Please state a source
Line 457 Standardly the result (the unique defect image / defectogram) is obtained from derivation. That you choose one frame from the processed sequence. Not from calculated coefficients (this is also often performed). I would expect Unique defect image next to the time sequence of the derivative. Can you please comment?
Line 486 electrical noise. What noise? IR camera? Surrounding? Etc.?
Line 524 equation (Dirac instead of equation(Dirac space was missing
Line 527 What is SDI?
Line 535 e is effusivity
Line 542 (equation 26) Shouldn’t it be DAC[i,j]
Line 563 and 565 Consider using they instead of he as the authors, not the author. This occurs in several places.
Line 599 (Figure 11) Why do you show X-ray CT-scan?
Line 614 [] there is a missing number in reference
Line 621 PPT instead of ppt
Line 633 they instead of we
Line 673 and figure 14. I don’t see any improvement in PCT with SPCT and ESPCT. The contrast may be better but most defects (indications) are visible worse. Could you please comment on it?
Line 675 Strange font
Line 689 Figure 15 The picture has very low quality.
Line 784 SHT … Is it step heating thermography? Maybe consider using SHT experiment. At first read, it was a bit confusing.
Author Response
Dear reviewer,
We thank the reviewers for their comments. The manuscript was faithfully revised according to the comments of the reviewers, and the text is marked in “red” text.
- We revised drastically of the manuscript according to reviewer's comments. We reduce subsection 2.3 and to focus just on "pulsed thermography". Therefore, the title was revised to “Lastest advances in common signal processing of pulsed thermography for enhanced detectability: A review”.
- Comments in "Green Box" are the contents of the deleted section and are not displayed in the body.
- Comments in minor remarks marked "in blue" have been revised in the text.
- Due to the permission problem, the result figures of other papers that were inserted into the manuscript were removed.
Lastly, a review of the active thermography signal processing and technology you suggested is partially added to Section 5.3. In the future, we will be able to submit papers on these algorithms through an in-depth review. Thanks again for the comments of the reviewer.
Author Response File: 
Author Response.docx
Reviewer 2 Report
See the attached report.
Comments for author File: Comments.docx
Author Response
Dear reviewer,
We thank the reviewers for their comments. The manuscript was faithfully revised according to the comments of the reviewers, and the text is marked in “red” text. Corrections and answers to each comment are as follows.
- We revised drastically of the manuscript according to reviewer's comments. We reduce subsection 2.3 and to focus just on "pulsed thermography". Therefore, the title was revised to “Lastest advances in common signal processing of pulsed thermography for enhanced detectability: A review”.
- Comments in "Green Box" are the contents of the deleted section and are not displayed in the body.
- The description of the TSR algorithm in Section 3 has been supplemented in more detail.
- (9), (10) and (11) have been supplemented in the text.
- . In Section 4, the description of the first introduction of each algorithm has been moved to each section in Section 3.
- Comments in minor remarks marked "in blue" have been revised in the text.
- Due to the permission problem, the result figures of other papers that were inserted into the manuscript were removed.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
Authors have implemented the manuscript according to my suggestions, so I recomend to publish it in the present form.
