Analysis of Infrared Spectral Radiance of O2 1.27 μm Band Based on Space-Based Limb Detection
Round 1
Reviewer 1 Report
This research based on the demand for near-infrared spectral radiance of O2 limb detected, proposed a method of spectral radiance calculation coupled with an atmospheric remote sensing model of limb detection.
This article is well written overall, but the article has a large number of English abbreviations that do not give all English words, which is not friendly to readers. The topic is relevant to the field and also addresses a specific gap in the field. A new method is proposed and analyzed.
The conclusions consistent with the evidence and arguments presented and addressed the main question posed.
This paper is well written and can be accepted as it is except some explainations of abbreviations.
Minor editing of English language required
Author Response
Replies to Comments by Reviewers#1
The authors are grateful to the Editor and reviewers for their treasure time, great effort and useful comments which help to revise the paper for a better quality. Based on the comments and suggestions, we have made modification on the original manuscript. In the subsequent correspondence, “Comments for Authors” are copied herein again in red color while “Replies to Reviewers” are written in blue color.
To Reviewer #1:
This research based on the demand for near-infrared spectral radiance of O2 limb detected, proposed a method of spectral radiance calculation coupled with an atmospheric remote sensing model of limb detection.
This article is well written overall, but the article has a large number of English abbreviations that do not give all English words, which is not friendly to readers. The topic is relevant to the field and also addresses a specific gap in the field. A new method is proposed and analyzed.
The conclusions consistent with the evidence and arguments presented and addressed the main question posed.
This paper is well written and can be accepted as it is except some explainations of abbreviations.
Answer: Thank you very much for your comments. This is the mistake we made during the proofreading process. We have proofread and corrected the abbreviations in the article:
SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY)
Greenhouse gas Observing SATellite (GOSAT)
Orbiting Carbon Observatory-2 (OCO-2)
Total Carbon Column Observing Network (TCCON)
WAves Michelson Interferometer (WAMI)
Doppler Asymmetric Spatial Heterodyne-spectroscopy(DASH)
HIgh-resolution TRANsmission molecular absorption database (HITRAN)
Thank you again for your comments!
Again, we are grateful to you for your efforts towards making this paper better in quality and readability. We have revised the paper in accordance with the comments and suggestions. Thank you again for your comments!
Replied by
Lu Bai
2023-9-19
Author Response File: 
Author Response.docx
Reviewer 2 Report
My main concern here is the originality and novelty of the content in this manuscript. Similar results have already been published in other articles. Could the authors please justify the novelty here?
It seems non-LTE and multiple scattering effects were taken into account in the modelling described by the authors. I think it is very important to consider these, in the O2-based limb detection.
How do the surface albedo, solar zenith angle, and aerosol loading affect the line shapes in the current model?
Basic grammar and typo check is required.
Author Response
Replies to Comments by Reviewers#2
The authors are grateful to the Editor and reviewers for their treasure time, great effort and useful comments which help to revise the paper for a better quality. Based on the comments and suggestions, we have made modification on the original manuscript. In the subsequent correspondence, “Comments for Authors” are copied herein again in red color while “Replies to Reviewers” are written in blue color.
To Reviewer #2:
My main concern here is the originality and novelty of the content in this manuscript. Similar results have already been published in other articles. Could the authors please justify the novelty here?
Answer: Thank you very much for your comments.
In the published literature, the detection of O2 1.27μm band is mainly analyzed by the fine spectral lines collected in the wind field measurement, but there is less basis for the selection of oxygen molecular spectral lines. In this paper, the spectral radiance of 1.27μm band of O2 is selected according to O2 molecular self-absorption, separation of spectral line and temperature sensitivity, and the most suitable spectral line for detection is given. Among them, the spectral line selection considering spectral line separability and temperature sensitivity is the originality and novelty of this paper.
Thank you again for your comments!
It seems non-LTE and multiple scattering effects were taken into account in the modelling described by the authors. I think it is very important to consider these, in the O2-based limb detection.
How do the surface albedo, solar zenith angle, and aerosol loading affect the line shapes in the current model?
Answer: Thank you very much for the reviewer’s comments.
In this paper, we analyze the effect of O2 spectral radiance on space-based limb detection. Because the line of sight is pointing toward the atmosphere and away from the surface. The effects of surface albedo, solar zenith Angle and aerosols on limb detection are small. and atmospheric background radiation is not considered in this paper. The surface albedo, solar zenith Angle and aerosols have significant effects on the model only when the detection line of sight is directed towards the surface. In subsequent studies, we will consider the effects of these parameters when considering the contribution of surface radiance.
Thank you again for your comments!
Again, we are grateful to you for your efforts towards making this paper better in quality and readability. We have revised the paper in accordance with the comments and suggestions. Thank you again for your comments!
Replied by
Lu Bai
2023-9-19
Author Response File: Author Response.docx
Reviewer 3 Report
This article presents an analysis of the best spectral lines for limb detection, particularly for O2 at 1.27 μm. The authors find that group R7R7, R7Q8 and group R11R11, R11Q12 282 spectral lines in the O2 1.27μm band are the best for the limb detection.
I find the analysis OK and I have no major problems with the method applied. Since this analysis is important for retrievals, it should be published.
Major:
I have only one major comment. Is it possible to demonstrate a retrieved temperature profile using the selected band, I mean, a simulated profile? This would strengthen the content of the paper. Other comments are minor.
Minor:
L 27: First sentence itself is grammatically not correct. Please pay attention to language errors. Some are given below, but not complete. Thank you.
L27: “Wind fields are”
I do not understand the first sentence of Introduction. Which atmospheric parameter? Wind itself is an atmospheric parameter in that sense
L51: not more optimal, just “optimal”
L54 and other places: space before the unit
L85: instead of “After that”, use “Then”
Figure 1 caption: l1 l2 etc parameters should be mentioned in the caption.
Figure 2: All the parameters and notations used in the figure should be mentioned in its caption.
L118 and at other places: “310 nm”. The space before unit.
L141: the reaction occurs exactly at 762 nm?
Figure 3 caption: explain the terms P, Q, and R in the caption
Line 176: “296 K”
L202: “large-scale objects”, it need not be a research object
Figure 4: Combine a and b figures. Why do you want to split the figure?
L 225: “10–90 km”
L 226: The US 1976 model is too old. Is there any other recent data available to be used?
Figure 6: You need to write what the R3R3 etc are in the caption. Also, please combine Figures 6 and 7
L275: Which HITRAN data base? Which year?
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Need a check on language errors.
Author Response
Replies to Comments by Reviewer#3
The authors are grateful to you for your treasure time, great effort and useful comments which help to revise the paper for a better quality. Based on the comments and suggestions, we have made modification on the original manuscript. In the subsequent correspondence, “Comments for Authors” are copied herein again in red color while “Replies to Reviewers” are written in blue color.
To Reviewer #3:
This article presents an analysis of the best spectral lines for limb detection, particularly for O2 at 1.27 μm. The authors find that group R7R7, R7Q8 and group R11R11, R11Q12 282 spectral lines in the O2 1.27μm band are the best for the limb detection.
I find the analysis OK and I have no major problems with the method applied. Since this analysis is important for retrievals, it should be published.
Major:
I have only one major comment. Is it possible to demonstrate a retrieved temperature profile using the selected band, I mean, a simulated profile? This would strengthen the content of the paper. Other comments are minor.
Answer: Thanks a lot for the comment. In this paper, it is possible to invert the temperature in the atmosphere by the temperature sensitivity of the radiance from the spectral lines of O2. For example, through the relationship between spectral lines R7R7 and R7Q8 and temperature, the higher the temperature, the lower the spectral line intensity, which can be used for temperature inversion. However, it is necessary to compare the satellite measurement data for temperature inversion to verify the correctness. At present, we have not obtained corresponding data for comparison. In subsequent studies, temperature inversion studies can be carried out using experimental measurement data.
Thank you again for your comments!
Minor:
L 27: First sentence itself is grammatically not correct. Please pay attention to language errors. Some are given below, but not complete. Thank you.
L27: “Wind fields are”
I do not understand the first sentence of Introduction. Which atmospheric parameter? Wind itself is an atmospheric parameter in that sense
Answer: Thanks a lot for the comment. We changed the description of the wind field to " Wind field is an important physical quantity that characterizes the atmospheric state ".
Line 27: Wind field is an important physical quantity that characterizes the atmospheric state
Thank you again for your comments!
L51: not more optimal, just “optimal”
Answer: Thanks a lot for the comment. We change "more optimal" to "optimal".
Line 51: "more optimal" to "optimal".
L54 and other places: space before the unit
Answer: Thanks a lot for the comment. We added a space before the unit.
L85: instead of “After that”, use “Then”
Answer: Thanks a lot for the comment. We change "After that" to "Then".
Line 85: "After that" to "Then".
Figure 1 caption: l1 l2 etc parameters should be mentioned in the caption.
Answer: Thanks a lot for the comment. We added the description "Where represents the initial radiance, represents the length of the nth layer. "
Line 100-101: "Where represents the initial radiance, represents the length of the nth layer. "
Figure 2: All the parameters and notations used in the figure should be mentioned in its caption.
Answer: Thanks a lot for the comment. We added the description "Where represents the Solar photolysis, represents the Collisional quenching, represents the Spontaneous emission, represents the Solar excitation. "
Line 109-111: "Where represents the Solar photolysis, represents the Collisional quenching, represents the Spontaneous emission, represents the Solar excitation. "
L118 and at other places: “310 nm”. The space before unit.
Answer: Thanks a lot for the comment. We added a space before the unit.
L141: the reaction occurs exactly at 762 nm?
Answer: Thanks a lot for the comment. The photochemical reaction produces spectral radiance near 762nm, so 762nm is used to represent a certain bandwidth of spectral radiance generated by the reaction.
Thank you again for your comments!
Figure 3 caption: explain the terms P, Q, and R in the caption
Answer: Thanks a lot for the comment. We added the description "Where P, Q, R represents the sets of "local" quantum number for upper and lower rotational states. "
Line 180-181: "Where P, Q, R represents the sets of "local" quantum number for upper and lower rotational states. "
Line 176: “296 K”
Answer: Thanks a lot for the comment. We added a space before the unit.
L202: “large-scale objects”, it need not be a research object
Answer: Thanks a lot for the comment. We changed the description "However, in practice, the optical thin hypothesis is not valid in research objects such as combustion and plasma, and the self-absorption effect will lead to changes in the structure of the emission spectrum. "
Line 208-210: "However, in practice, the optical thin hypothesis is not valid in research objects such as combustion and plasma, and the self-absorption effect will lead to changes in the structure of the emission spectrum. "
Figure 4: Combine a and b figures. Why do you want to split the figure?
Answer: Thanks a lot for the comment. We merged the two figures.
L 225: “10 – 90 km”
Answer: Thanks a lot for the comment. We added a space before the unit.
L 226: The US 1976 model is too old. Is there any other recent data available to be used?
Answer: Thanks a lot for the comment. We choose the 1976 standard atmospheric model in this paper, because the 1976 standard atmospheric model is widely used in the simulation of atmospheric background radiance model, and has a certain accuracy. It is a relatively general model, and the atmospheric profile observed by satellite can be considered to simulate the spectral radiance of O2 under actual observation conditions in the subsequent research.
Thank you again for your comments!
Figure 6: You need to write what the R3R3 etc are in the caption. Also, please combine Figures 6 and 7
Answer: Thanks a lot for the comment. We added the description "(group R3R3, R3Q4, group R7R7,R7Q8 and group R11R11, R11Q12.)".
Line 258: (group R3R3, R3Q4, group R7R7,R7Q8 and group R11R11, R11Q12.)
As for Figure 6 And Figure 7, Figure 6 focuses on the influence of spectral line separateness on the selection of spectral lines when the radiance intensity is satisfied, and Figure 7 describes the influence of temperature sensitivity on the initially screened spectral lines, both of which are progressive. Therefore, we hope to keep Figures 6 and 7 to describe the selection of spectral lines.
Thank you again for your comments!
L275: Which HITRAN data base? Which year?
Answer: Thanks a lot for the comment. In this article we use the latest HITRAN2020 database. The HITRAN2020 database was updated in 2020.
Thank you again for your comments!
Again, we are grateful to you for your efforts towards making this paper better in quality and readability. We have revised the paper in accordance with the comments and suggestions. Thank you again for your comments!
Replied by
Lu Bai
2023-9-19
Author Response File: Author Response.docx
Reviewer 4 Report
There are 2 comments in total.
(1) Describe the chart more clearly. Suggest the author to supplement the corresponding relationship between the double vertical coordinates and different shapes in Figure 2. The two lines’ overlapping in Figure 4, making it difficult to distinguish " Without self absorption " and " With self absorption ". Suggest arranging them separately.
(2) It is recommended that the author unify the wavelength units in the entire text as wavenumber or wavelength. The abscissa in Figures 5, 6, and 7 is the wavenumber, but the unit nm appears multiple times in the text description.
Author Response
Replies to Comments by Reviewer#4
The authors are grateful to you for your treasure time, great effort and useful comments which help to revise the paper for a better quality. Based on the comments and suggestions, we have made modification on the original manuscript. In the subsequent correspondence, “Comments for Authors” are copied herein again in red color while “Replies to Reviewers” are written in blue color.
To Reviewer #4:
There are 2 comments in total.
(1) Describe the chart more clearly. Suggest the author to supplement the corresponding relationship between the double vertical coordinates and different shapes in Figure 2. The two lines’ overlapping in Figure 4, making it difficult to distinguish " Without self absorption " and " With self absorption ". Suggest arranging them separately.
Answer: Thank you very much for your comments. We have modified Figure 2 to link the wavenumber, molecular energy and energy level with dotted lines to indicate the correspondence. At The same time, the description is added under Figure 2. (The left axis represents the wavenumber generated by the molecular transition, and the right axis represents the energy of the molecule in that energy state.)
Figure 2. Schematic diagram of the photochemical processes of O2 in the earth's atmosphere
We made some modifications to Figure 4. The figure 4 on the left indicates that the self-absorption effect of O2 is not obvious at high limb height, so the radiance overlap is high; the figure 4 on the right indicates that the self-absorption effect of O2 is significant at low limb height, and the radiance difference is obvious.
(2) It is recommended that the author unify the wavelength units in the entire text as wavenumber or wavelength. The abscissa in Figures 5, 6, and 7 is the wavenumber, but the unit nm appears multiple times in the text description.
Answer: Thank you very much for your comments. We have changed the whole part of the result analysis in the paper in wavenumber, and only 1.27μm is used as the introduction in the Introduction and Data and Methods part of the paper.
Thank you again for your comments!
Again, we are grateful to you for your efforts towards making this paper better in quality and readability. We have revised the paper in accordance with the comments and suggestions. Thank you again for your comments!
Replied by
Lu Bai
2023-9-19
Author Response File: Author Response.docx
Reviewer 5 Report
Review of “Analysis of Infrared Spectral Radiance of O2 1.27 mm Band Based on Space-Based Limb Detection”” by Jingyu Bai et al.
The article describes a method of spectral radiance calculation coupled with atmospheric remote sensing model of limb detection. The limb IR radiance in the 1.27 mm band were simulated in a standard atmosphere using the line data from HITRAN database, and the most suitable spectral lines for detection identified. The article is original in its research contents, and I suggest accepting it for publication with minor edits. My comments and queries are listed below:
1. In the line after equation 10, N0, T0, and P0 are not properly written (subscripts).
2. On line 228-229, “4.5 ´ 10-16 ” needs to be written properly and in the same line.
3. In the Standard Atmospheric Model considered any loss of light due to scattering considered (in addition to the absorption at the specific lines)? If so, what are the scattering elements? While O2 absorption lines in the proposed band is useful for trace gas detection and quantifications by specifying the pathlengths, this could also be used for getting information for atmospheric aerosol presence and quantification.
4. The authors have used optical thin hypothesis to account for molecular self-absorption effect. The equation 17 was used for modelling this. What is the origin of this equation? The reference is missing. If it is derived in this paper, basic assumption used to arrive at this correction factor would be beneficial to the reader.
5. Is there an experimental evidence or validation study for the molecular self-absorption factor adopted in this paper? This would be beneficial to the reader on the significance and correctness of this correction factor
6. The figure 4 shows the simulated spectral radiance at the proposed band with and without self-absorption correction. An actual set of measured data would be beneficial to compare, if available from the database (TCCON database, for example).
7. The effect of line broadening was considered, and line selections were proposed for appropriate application considering selectivity and sensitivity in the paragraph starting at line 235. This a good strategy. One concern here is that the maximum resolution at which measurements can be taken is altitude dependent. Would selection of different lines for different altitudes improve the selection and reduced uncertainty?
Comments for author File: 
Comments.pdf
Author Response
Replies to Comments by Reviewer#5
The authors are grateful to you for your treasure time, great effort and useful comments which help to revise the paper for a better quality. Based on the comments and suggestions, we have made modification on the original manuscript. In the subsequent correspondence, “Comments for Authors” are copied herein again in red color while “Replies to Reviewers” are written in blue color.
To Reviewer #5:
Review of “Analysis of Infrared Spectral Radiance of O2 1.27 mm Band Based on Space-Based Limb Detection”” by Jingyu Bai et al.
The article describes a method of spectral radiance calculation coupled with atmospheric remote sensing model of limb detection. The limb IR radiance in the 1.27 mm band were simulated in a standard atmosphere using the line data from HITRAN database, and the most suitable spectral lines for detection identified. The article is original in its research contents, and I suggest accepting it for publication with minor edits. My comments and queries are listed below:
1. In the line after equation 10, N0, T0, and P0 are not properly written (subscripts).
Answer: Thank you very much for your comments. This is the mistake we made during the proofreading process. We have proofread and corrected the subscripts in the article.
Line 163-164: , , and .
2. On line 228-229, “4.5 ´ 10-16 ” needs to be written properly and in the same line.
Answer: Thank you very much for your comments. We have written the numbers and units properly and in the same line.
Line 230: 4.5*10-16(W/m2·sr·cm-1)
3. In the Standard Atmospheric Model considered any loss of light due to scattering considered (in addition to the absorption at the specific lines)? If so, what are the scattering elements? While O2 absorption lines in the proposed band is useful for trace gas detection and quantifications by specifying the pathlengths, this could also be used for getting information for atmospheric aerosol presence and quantification.
Answer: Thank you very much for your comments. In the Standard Atmospheric Model, the scattering of atmospheric radiance by cloud and surface is considered when calculating atmospheric background radiance. In this paper, temperature, pressure and particle number density of O2 change with height were obtained from the standard atmospheric model, the influence of spectral radiance generated by O2 itself on the limb detection is considered, and the influence of other elements on the radiance is not considered.
4. The authors have used optical thin hypothesis to account for molecular self-absorption effect. The equation 17 was used for modelling this. What is the origin of this equation? The reference is missing. If it is derived in this paper, basic assumption used to arrive at this correction factor would be beneficial to the reader.
Answer: Thank you very much for your comments. We annotated references that considered molecular self-absorption, which described "In the case of limb-viewing simulation, the spectral radiance is typically a straightforward Abel-type integration of the source function profile along the line-of-sight path. However, for the infrared atmospheric band O2 (a1Δg, v′ =0) →O2(X3Σg, v′′=0), the spectral radiance is modified by the attenuation due to the self-absorption of O2 molecules in the ground state. "
Line 201: "At the same time, the molecular transition radiates photons, and the photons will be re-absorbed by the same kind of particles in the ground state during the propagation process, that is, the self-absorption effect of photons[20]. "
Thanks again for the suggestions!
[20]Wu, K.; Fu, D.; Feng, Y.; Li, J.; Hao, X.; Li, F., Simulation and application of the emission line O19P18 of O2(a1Δg) dayglow near 1.27 mum for wind observations from limb-viewing satellites. Optics Express 2018, 26, (13), 16984-16999.
5. Is there an experimental evidence or validation study for the molecular self-absorption factor adopted in this paper? This would be beneficial to the reader on the significance and correctness of this correction factor
Answer: Thank you very much for your comments. The self-absorption effect considered in this paper is the absorption and emission of the back layer medium to the front layer medium considered by line-of-sight (LOS) method. We have not done experiments to test the self-absorption effect. In future studies, we will consider experiments to verify the phenomenon of molecular self-absorption.
Thanks again for the suggestions!
6. The figure 4 shows the simulated spectral radiance at the proposed band with and without self-absorption correction. An actual set of measured data would be beneficial to compare, if available from the database (TCCON database, for example).
Answer: Thank you very much for your comments. The observation path adopted in this study is the limb observation path of space-based exploration, and the molecular model we consider is one type of O2, so it is difficult to compare with the experimental observation data. The self-absorption effect of mixed gas may be considered in the subsequent research, so as to verify the correctness of the theory.
Thanks again for the suggestions!
7. The effect of line broadening was considered, and line selections were proposed for appropriate application considering selectivity and sensitivity in the paragraph starting at line 235. This a good strategy. One concern here is that the maximum resolution at which measurements can be taken is altitude dependent. Would selection of different lines for different altitudes improve the selection and reduced uncertainty?
Answer: Thank you very much for your comments. In this paper, we mainly consider the most suitable spectral lines of O2 at altitudes where the radiance intensity is strongest. The fine spectral lines most suitable for detection may be different for higher or lower altitudes, so different conclusions may be drawn for different altitude ranges. Choosing different spectral lines for different altitudes will lead to more applicable conclusions and reduce uncertainty.
Thank you again for your comments!
Again, we are grateful to you for your efforts towards making this paper better in quality and readability. We have revised the paper in accordance with the comments and suggestions. Thank you again for your comments!
Replied by
Lu Bai
2023-9-19
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
Thank you authors for responding to my comments.
Basic typo and grammar checks are recommended before publication.
