Hybrid Coded Excitation of the Torsional Guided Wave Mode T(0,1) for Oil and Gas Pipeline Inspection

Round 1

Reviewer 1 Report

The topic of the article is relevant. To increase the signal–to-noise ratio, you can use a well-known technique - to use complex signals. However, the choice of complex signals with a minimum level of "side lobes" (PSL) is not a trivial task, which the authors of the article solve by proposing BCG technology.

Why in Fig. 4a do not indicate that the code B3 G4 is shown? By the way, which of the complementary pair? And how it agrees with the code 121-1-21! Its schematic view looks more correct in Fig. 3!!!

In Fig. 4a it is necessary to indicate that this is a type of different complex signals. According to Fig. 4, for the B3G4 code, PSL = -23.4 dB, and in Fig. 4b the level of "side lobes", in my opinion, is higher. And in general, nine graphs in one figure are simply difficult to distinguish.

In Table 1, it should be indicated that the 6-bit BCG is B3G4.

It would be nice to make drawings for Fig. 8 when studying a simple echo signal and B3 G4, which is emphasized in the article. In Fig. 8, echo signals after compression? How exactly was the SNR calculated in Table 2 and the others?

And why are there no PSL columns in Table 3?

In Figure 9, many graphs are simply indistinguishable. The BCD type should be indicated on the charts. Why in Fig. 9a a huge level of "side lobes" (according to Fig. 10 PSL is approximately -23 dB)? After all, echo signals after compression! I did not understand what gives the reader the view of the spectrum in Fig. 9b!

In table 4 BCG = B3G4?

I would not say that the phrase "The theoretical and experimental testing results of the SNR and PSL have a good agreement" given in the conclusion is correct. In Fig. 10, the theoretical graphs differ from the experimental ones by up to 10 dB! Is it really possible to say after that that theoretical calculations are close to experimental ones?

Author Response

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Reviewer 2 Report

Considering  that modulating Golay code sequence with Barker sequence for ultrasound imaging has been suggested before by Kim et al., and as the authors claim that this the first time that such a hybrid coded excitation technique is used for pipe inspection (line 80),

What are the other methods for pipe inspection? You should compare your methods with them (citing their papers), and with not with yours, using different parameters and codes (for example Figure 10)

Figure 9 (a): the logarithmic values give a better presentation+ this image does not show a reduced side lobe level of BCG code compared with the other codes.

Author Response

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