Experimental Study on the Thermal Infrared Spectral Variation of Fractured Rock
, Shanjun Liu 2,*, Wenfang Liu 2, Chunju Zhang 1, Shuiping Li 1, Min Yu 1 and Lixin Wu 3Round 1
Reviewer 1 Report
This paper deals with the problematic of the weight of emissivity parameter regarding relief changes as fractures. The paper is clear and well -written.
Only small questions arise during lecture:
1/ Fig 7: The radiation schema is a bit confusing. If the radiation from inside the fissure travels perpendicular to the wall, rebounding, why arriving close to the surface it changed its path and became normal to the intact surface? The highest radiation/emissivity values should be normal to the fissure wall but with an angle to the measurement equipment (as in Fig. 10). If authors consider that no angle is needed to be taken into account for the equation values, please arrange the graph to delete the signal rebounding.
2/ Is it possibly that the radiation increase in extensional fractures was rather influenced by temperature and that would explain clearly the observed behaviour? Meanwhile, in bulging, the emissivity is the control parameter...
3/ line 345: why authors chose n=2? In the Figure 8 only one reflection was shown (n=1). Please justify.
4/ Fig 1: please improve resolution
Author Response
Responses to Reviewer #1
Thank you very much for the positive and constructive comments and suggestions on our manuscript. This manuscript has been revised carefully based on these comments.
Comment (1)
Fig 7: The radiation schema is a bit confusing. If the radiation from inside the fissure travels perpendicular to the wall, rebounding, why arriving close to the surface it changed its path and became normal to the intact surface? The highest radiation/emissivity values should be normal to the fissure wall but with an angle to the measurement equipment (as in Fig. 10). If authors consider that no angle is needed to be taken into account for the equation values, please arrange the graph to delete the signal rebounding.
Response 1:
Sorry for the confusing arrange in Fig. 7.
Firstly, the maximum radiation from the inside the fissure travels perpendicular to the wall, and arrive to the surface after multiple reflections. The effective emissivity caused by the cavity effect is the accumulation result. So the increase in reflections can lead to the increase in the value of effective emissivity in the Equation (6).
Then, the radiation from the intact region and fractured region is emitted to the whole hemisphere. Because of the observation view angle, distance and the arrangement of spectrometer, the radiation emitted from the circular observation area within a certain angle range can be received by the spectrometer. Thus, the radiation in a relative large angle could not be received by the spectrometer.
The Figure 7 has been repainted and the description of Figure 7 has been updated in Line 332-335.
Comment (2)
Is it possibly that the radiation increase in extensional fractures was rather influenced by temperature and that would explain clearly the observed behaviour? Meanwhile, in bulging, the emissivity is the control parameter.
Response 2:
Thank you for the comment. According to the previous studies and the measured results in Figure 3, the temperature changed throughout the entire rock loading process because of the thermoelastic effect and fiction heating effect. Therefore, the radiance is influenced by temperature in the entire process as well. According to the Equation (5), if there is no variation on emissivity, Δε(λ) = 0, ΔL1(λ) = ΔLT(λ). The wavelength feature of ΔLT(λ) is similar to that of the ε(λ) when the temperature increase. And the wavelength feature of ΔLT(λ) is opposite to that of the ε(λ) when the temperature decrease. Therefore, the influence of temperature change on the amplitude of ΔL1(λ) is more obvious than that on the wavelength features. The contribution of emissivity change has been discussed in Line 491-506.
Generally, the temperature decreases in the extensional fractures without the friction heating effect. The decrease in temperature can lead to the decrease in radiance in the intact region without considering the emissivity change. The result is contrary to the observed behaviour in Figure 4. So the influence of emissivity change on the radiance change is more significant. The analysis on the simulated and measured results based on the measured temperature has been discussed in Line 387-395.
Additionally, the temperature decrease because of the stress relaxation and dissipation. The decrease in temperature can lead to the decrease in radiance in the local bulging fractures.
Therefore, we can conclude that the radiance variation is the combined effect of changes in both temperature and emissivity.
Comment (3)
line 345: why authors chose n=2? In the Figure 8 only one reflection was shown (n=1). Please justify.
Response 3:
Sorry for the mistake, the value of n has been corrected as 1 in Line 355 in the revised manuscript. The simulated result of effective emissivity is used to explain the wavelength features of Δε(λ), which is corresponding to the wavelength feature of the radiance increment curve in the extension fracture.
Comment (4)
Fig 1: please improve resolution.
Response 4:
Thank you for the kind suggestion, the Figure 1a and 1b have been updated in the revised manuscript.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Title: Experimental study on the thermal infrared spectral variation of fractured rock
General comments
The paper is related to spectral emissions during rock fracturing under loading.
The paper is well written and well organized.
Results are clearly presented and references are adequate
Conclusions are supported by the results.
Detailed comments
Line 120: AE?
Line 232: please specify what is the similarity coefficient and how it is computed
Line 243: please specify the ε(λ) function
315 I suggest replace “… are analyzed separately below” in “… are analyzed separately in the followings paragraphs.”
Line 378 from 288.81 K to 288.68 °C difference is 0.13°C
Line 512 CO or Co2?
Conclusion: please add future study that can be performed
Author Response
Responses to Reviewer #2
Thank you very much for the positive and constructive comments and suggestions on our manuscript. This manuscript has been revised carefully based on these comments.
Comment (1)
Line 120: AE?
Response 1:
AE is the abbreviation of acoustic emission, which is used to detect the generation and development of fractures in the rock loading process. The description of AE has been added in the Line 121-123 in the revised manuscript.
Comment (2)
Line 232: please specify what is the similarity coefficient and how it is computed
Response 2:
To quantitatively assess the similarity of these six radiance increment spectra, the average radiance spectrum for these six samples, which is defined as ΔLz(λ), was calculated. And the similarity coefficients between the six spectra and the ΔLz(λ) spectrum were calculated.
The calculation equation of similarity coefficient can be defined as follow:
The six spectra can be expressed as ΔLi(λ), i = 1-6. λk is the k th wavelength, n is the number of wavelength in the entire wave range. And ΔLi(λk) is the radiance value at λk on ΔLi(λ). .
All the similarity coefficient results are larger than 0.9. The shape and wavelength feature of these six spectra is almost uniform. If the similarity coefficient is 1, the shape of these spectra are uniform. The description of similarity coefficient and Figure 4 has been revised in Line 233-238
Comment (3)
Line 243: please specify the ε(λ) function
Response 3:
ε(λ) is the emissivity spectrum of sandstone surface in the static condition, which can indicate the value of spectral emissivity at different wavelengths. The wavelength features of ε(λ) can be used to identify the mineral and rocks. The description of ε(λ) has been revised in Line 248-249.
Comment (4)
315 I suggest replace “… are analyzed separately below” in “… are analyzed separately in the followings paragraphs.”
Response 4:
Thank you for your kind suggestion. The description has been replaced in the Line 321.
Comment (5)
Line 378 from 288.81 K to 288.68 °C difference is 0.13°C
Response 5:
Sorry for the calculation mistake. The difference from 288.81 K to 288.68 K is -0.13 K. The value has been corrected in Line 388.
Comment (6)
Line 512 CO or Co2?
Response 6:
Sorry for the mistake. The CO has been replaced by CO2. The description has been replaced in Line 521.
Comment (7)
Conclusion: please add future study that can be performed
Response 7:
The further studies on the different mineral composition and fault structure have been added in the Line 580-584 in the conclusion.
Author Response File: Author Response.docx
