Impact of Topographic Correction on PRISMA Sentinel 2 and Landsat 8 Images

Round 1

Reviewer 1 Report

Review report on “Impact of topographic correction on PRISMA Sentinel 2 and Landsat 8 images”

Overall comments:

 

The topic of the manuscript is interesting, however, I was expecting results in the form of spatial maps as well as scatter plots. It would be great if the authors show validation results against ground measurements before and after applying topographic correction (TC) during the atmospheric correction process. Also, it would be interesting if the authors show the spatial differences with and without “TC”. 

Author Response

Reviewer 1

Review report on “Impact of topographic correction on PRISMA Sentinel 2 and Landsat 8 images”

Overall comments:

The topic of the manuscript is interesting, however, I was expecting results in the form of spatial maps as well as scatter plots. It would be great if the authors show validation results against ground measurements before and after applying topographic correction (TC) during the atmospheric correction process. Also, it would be interesting if the authors show the spatial differences with and without “TC”. 

The authors would like to thank the reviewer for valuable suggestions.

Spatial maps were added as suggested.

As regards ground measurements, this work concerns a statistical approach which is useful when it is difficult to acquire soil measurements or when these are in any case absent. As explained in the text, this method has the advantage of not being limited only to the points for which the ground measurements are available but allows a statistical analysis applicable to each point of the image. A comparison with the ground measurements before and after the TC is found in Pignatti et al. 2022. The bibliographic reference has been added to the text.

Spatial analysis with and without TC was added

Author Response File: Author Response.docx

Reviewer 2 Report

This study focuses on the impact of topography in the ground reflectance retrieval of roughness terrains from satellites optical remote sensing data. The authors used the difference in remote sensed ground reflectance between two different illumination conditions to assess the impact of topography in flat and steep terrains. The results show the improvement in ground reflectance retrieval in roughness terrain with topographic correction. 

 

The topographic impact is a well known issue. At present, some comments are being considered to improve the quality of the manuscript.

1. The statement of relative works is short. A lot of references but few comments.

2. The lack of description of the study area. What type of surface in this study area? Almost no useful information can be found in Figure 1. A satellite image and a topographic map would be helpful for better understanding of the test site.

3. Line 189, What is the zenith and azimuth of the sun for these dates?

4. Line 302, Figure 5: According to the definition of RI (Relative Improvement) by Eq4, its positive value means that MRAD_ATC > MRAD_SAC? Which is contrary to Figure 4.

5. Check typing error: line 107 in Eq1 B*rho_e instead of B*rho, line150 “ground trough”,…

Author Response

Reviewer 2

The authors thank the reviewer for helpful comments and suggestions

This study focuses on the impact of topography in the ground reflectance retrieval of roughness terrains from satellites optical remote sensing data. The authors used the difference in remote sensed ground reflectance between two different illumination conditions to assess the impact of topography in flat and steep terrains. The results show the improvement in ground reflectance retrieval in roughness terrain with topographic correction. 

 

The topographic impact is a well known issue. At present, some comments are being considered to improve the quality of the manuscript.

1. The statement of relative works is short. A lot of references but few comments.

The comments on the cited bibliography have been extended.

 

2. The lack of description of the study area. What type of surface in this study area? Almost no useful information can be found in Figure 1. A satellite image and a topographic map would be helpful for better understanding of the test site.

The study area has been better described. Figure 1 has been improved and a satellite image and an hill shade image describing the topographyc behaviour have been added to better represent the study area

.

3. Line 189, What is the zenith and azimuth of the sun for these dates?

Zenith and azimuth have been added, thanks for the tip

 

4. Line 302, Figure 5: According to the definition of RI (Relative Improvement) by Eq4, its positive value means that MRAD_ATC > MRAD_SAC? Which is contrary to Figure 4.

Thank you so much for checking the equations carefully. equation 4 has been corrected and is now consistent with figure 5 and the rest of the text

 

5. Check typing error: line 107 in Eq1 B*rho_e instead of B*rho, line150 “ground trough”,…

Thank you very much. Equation 1 has been corrected and "trough" has been replaced with "truths".

 

Author Response File: Author Response.docx

Reviewer 3 Report

Please see the attached file.

Comments for author File: Comments.pdf

Author Response

Reviewer 3

 

In this paper, possible effects of topography corrections introduced in atmosphere corrections in satellite multispectral surface reflectivity imaging of PRISMA, Sentinel-2 and Landsat-8 has been considered. The study was based on the analysis of the images acquired in mountainous environment and used two atmosphere tools by statistical comparison between reflectance images of the same scene under different illumination conditions. Two indices are introduced in analysis: MRAD (mean over pixels relative summer-winter difference between the reflectance images) – as estimator of the error associated with atmosphere correction procedures, and PI (spectral relative improvement coefficient – relative difference of MRAD obtained with and without the topography correction) to estimate the improvement obtained with the introduction of topography in the atmosphere correction.

As results that demonstrate the efficiency of the proposed topography correction, spectral dependences of MRAD and PI for cases of flat areas and the highest slopes on the scene are presented – as well as the dependences of these parameters on the slope gradient.

Results are interesting and useful; however I have some comments:

 

1. To make the paper self-explanatory and provide the possibility to use results of the paper for readers, parameters in formulas should be introduced explicitly.

Parameters in formula has been introduced explicitly as suggested

 

2. The formula (1) should be written as

Thanks for noticing the inconsistency in the formula. Equation 1 has been corrected:

 

3. It is my advice to simplify and make the notation more physically convenient: use R instead of L for radiance; φ, φ_n, φ_sci instead of SZA, SnA. slA. The term “the portion of the sky viewed by the target” for slA is not clear.

The notation has been simplified as requested. SZA has been replaced by θ_s, SnA by θ_n. The formula has been modified introducing the angle α between the inclined surface and the horizontal plane. As for the radiance, it is preferred to continue to use L to avoid confusion with the Reflectance which is normally indicated by R. The same notation is used by ENVI-FLAASH, by 6S and many other software for atmospheric corrections.

 

4. Multiple use of abbreviations should be avoided.

Abbreviation have been reduced in the text

 

I recommend to publish this paper after revision according these comments

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Thanks to the authors for the added comments on state of the art, however, I shall consider that the references [3, 4, 5] are not necessary, especially the self-citation [5] is not appropriate. I suggest removing these references. For the rest of the changes, it is OK.

Author Response

References 3,4,5 have been removed as suggested. Thank you very much for your support