Determining the Optimal Sample Size for Assessing Crown Damage on Color Infrared (CIR) Aerial Photographs

Round 1

Reviewer 1 Report

In its present form this paper does not tell the reader what specific CIR technology you are using, the details of how you are assessing the damage, what pests and disease species are causing the tree dieback, and details of the nature of the forest you are studying including the tree species.  A valuable previous paper of yours - ref 25- has a more desirable level of detail than the current paper.  

Many of the references that could supply that information are in journal articles and theses that cannot be easily obtained outside of Croatia.  Please wherever you cite these difficult to obtain papers – either provide links to online versions of the text or bring many of the details into the current paper.

In general how do the problems of these forests fit into the study of comparable forest dieback elsewhere?   Where does your study fit in with other studies assessing appropriate sample size?  Diseases and insect pests have many different spatial patterns - how likely is it that your findings can be generalized?   

16  dominant tree species? elevation? location? (an abstract should assume minimal background knowledge)

47  cite ref 37 here  or use a translated quote from ref 37

Requires minor editing

Author Response

Dear Reviewer,

first of all I want to thank you because your comments contributed to the improvement of this article.

In its present form this paper does not tell the reader what specific CIR technology you are using, the details of how you are assessing the damage, what pests and disease species are causing the tree dieback, and details of the nature of the forest you are studying including the tree species.  A valuable previous paper of yours - ref 25- has a more desirable level of detail than the current paper.  

Many of the references that could supply that information are in journal articles and theses that cannot be easily obtained outside of Croatia.  Please wherever you cite these difficult to obtain papers – either provide links to online versions of the text or bring many of the details into the current paper.

• the requested changes were made to the article and the work methodology was clarified

In general how do the problems of these forests fit into the study of comparable forest dieback elsewhere?   Where does your study fit in with other studies assessing appropriate sample size?  Diseases and insect pests have many different spatial patterns - how likely is it that your findings can be generalized?   

• Decaying of trees is a problem which is present almost in the entire Europe and World, and has been a long long current topic in area of Croatia. The negative consequences of forest degradation are tried to be reduced by implementing economic measures and monitoring the health status of trees, i.e. by assessing crown damage. Determining the health status of forests is carried out, apart from the terrestrial method and methods of remote research - interpretation of infrared color (ICK) aerial photographs.
• Research possibility of applying infrared color (CIR) aerial photographs was carried out by many scientists in Europe and the World (Masumy 1984, Hočevar and Hladnik 1988,  Ekstrand 1994, Innes and Koch 1998, Butler and Schlaepfer 2004, Ciesla 2009, Wulder et al. 2012, Eigirdas et al. 2013, Lehmann et al. 2015,  Dash et al. 2017, Safonova et al. 2019).
• Also in Croatia research was conducted on possibilities application of remote sensing methods in forestry (Pernar 1994, Kušan 1996, Pernar 1997, Pernar and Klobučar 2003, Pernar et al 2007a, 2007b, Klobučar and Pernar 2009, Pernat et al. 2011, Seletković et al 2011, Balenović et al 2011, 2015, 2017, Kolić et al 2015, 2018, Ančić et al 2019, Pernar et al 2020).
• Normally, a systematic sample of 100x100 is used when interpreting the recordings, so that was the reason for conducting this research, so as not to interpret too many trees, i.e. to save time and money, while maintaining the same accuracy.

16  dominant tree species? elevation? location? (an abstract should assume minimal background knowledge)

• it is supplemented in the article

Reviewer 2 Report

See attached file.

Comments for author File: Comments.pdf

None.

Author Response

Dear Reviewer,

first of all I want to thank you because your comments contributed to the improvement of this article.

In general, the methods needs a complete overhaul. Most of the figures are not required, and I would take inspiration from the methods section in other papers to put this together in a more logical and systematic manner. There also seems to be a missing section which describes how the accuracy was calculated, so what exactly is the validation data, and so on. I found it not possible to fully understand how this was done. Not having clear methods means that evaluating the manuscript is difficult.

• in the article, the parts of the text that describe the methodology of the work and give a clearer idea of the conducted research and the obtained results have been supplemented

Please check whether some of the papers on sampling approaches by Steve Stehman, or Pontus Olofsson would be relevant. Perhaps not, but they have some guidance on stratified sampling approaches, which I find useful

• Thank you for the suggestion. Papers are useful but not relevant to this research.

I'd also appreciate some more info about the type of damage we are seeing and how it is interpreted in the images.

• In the introductory part, it was added which damages are observed in the recordings and how this is reflected in the near infrared part of the spectrum.

Line 47 - stratum are mentioned, but it's not clear what type of strata we are talking about

• By the term stratum, we meant the sub-compartments (it was added in parentheses)

Line 75-77 - I presume this selection of the dot system was a comparison with the raster method mentioned above?

• That's right, the written fact referred to previous research: “…In all the research to date, a dot grid sample proved best, because it is well distributed in space. Since it interprets a much larger number of trees, it is equally reliable compared to field assessment. …”

Line 83 - you mention a primary goal. Are there any secondary/sub goals? It might be worth listing them here too

• In the article, in addition to the main goal, the goals that enabled the main goal of the work to be realized were also supplemented.

Figure 1 - please add a scale, and some more info in the caption, which should include the region, and what the blue and red lines are

• In the text, above the picture, it is stated which area it is about, and the coordinates are indicated, and in the title of the picture what the red and blue polygons indicate.

Figure 2 - I'd say this is not necessary, and should be removed.

• The image has been removed from the text.

Lines 97-108. I'd make these more descriptive on what the steps are accomplishing, rather than being rather technical and not descriptive in terms of what they are for. I would also remove the bullet points.

• Thanks for the advice, but it seems clearer if the text remains written in its current form.

Fig 3 I'd say should also be removed.

• The image has been removed from the text.

Table 1. information like the project name is not needed. It's not clear what the purpose of this table is. It should be clear, that it is for example to show the different sites, or availability of validation data, or sampling design.

• The table 1 has been removed from the text.

Figure 4 also could be removed, and figure 5, and figure 6. I would instead add a clear figure which shows the sampling design (mentioned earlier), and an example of a crown damaged tree within one of the sites

• Images have been removed from the text.

figure 7 - this should be brought nearer the beginning of the methods section. In the caption, I think it is the first time the phrase 'survey strip' has been used, so this should be explained earlier

• phrase ' survey strip ' - explanation added earlier in the text

Figure 8 - this needs some more explanation, as it is difficult to follow as it is. For example, do you need all three boxes, or would the first one suffice?

• To explain the methodology of the work, it is necessary to observe all three parts of the picture, because it is clarified what was the position of the trees, taken for research, in relation to the laid systematic sample.

Also in the caption , it mentions position 4,2 1 but is this not just the number of trees selected, and the letters should be mentioned in the caption

• Letters have been added, which indicate the position of the tree on the systematic pattern.

Table 2 - I don't follow what is meant by degree of damage, and the codes used. I wonder whether something more self explanatory than 2A etc. could be used?

• For easier understanding of the text, individual degrees of damage and their labels have been added in the introductory part of the article.

Reviewer 3 Report

The paper proposes a methodology to detect crown damage using aerial photos. For that purpose, the authors compared different sizes of samples. The authors provided statistical and visual outputs of the research, however, some missing parts need to be improved for the applied methodology. The authors should consider the suggestions and answer the questions given below;

1.       The abstract: Please add the main quantitative result of the research.

2.       Page 2 line 66: please add the references for the statement.

3.       In the introduction the aim of the study is not clear, what is missing in the literature? How do the authors contribute to that?

4.       In section 2: write the name of the country where the study area is. Give details about the study area such as topography, forest density, and percentage of forest cover for the season.

5.       In section 2:  give the details about the images: image acquisition dates, season, and spatial resolution.

6.       Please briefly describe damage, mean damage, and damage index in the paper.

7.       In Figure 1: add coordinates and scale for the selected subregion.

8.       Figures 2, 3, 4, and 5 are not necessary. It looks like more tutorial than a research paper. These are the main preprocessing steps of a photogrammetric product assessment.

9.       Page 6 line 149: add references for the earlier researches mentioned here.

10.   Page 8: the level of significance according to the X2-test should be given in the paper.

11.   Page 9: In tables 3 and 4, two digits are enough after the comma.

12.   In Table 4: write what Sx and S2 are in the caption.

13.   Figures 9 and 10: write the titles of the axes.

14.   Table 6: in the caption of the table, write the long version of the abbreviations.

15.   Discussion is limited, expand it considering the previous studies which are mentioned in the introduction.

Author Response

Dear Reviewer,

first of all I want to thank you because your comments contributed to the improvement of this article.

The abstract: Please add the main quantitative result of the research.

• the research results were added to the abstracts

In the introduction the aim of the study is not clear, what is missing in the literature? How do the authors contribute to that?

• in the introduction, the research objective was added and clarified

In section 2: write the name of the country where the study area is. Give details about the study area such as topography, forest density, and percentage of forest cover for the season.

• In the section 2, something more was added about the research area (altitudes, phytocenoses, tree species, ...)

In section 2:  give the details about the images: image acquisition dates, season, and spatial resolution.

• In section 2, the details about the images have been added

Please briefly describe damage, mean damage, and damage index in the paper.

• Indicators of damage are briefly described in the section on work methodology

In Figure 1: add coordinates and scale for the selected subregion.

• Coordinates are added to the text above Figure 1

Figures 2, 3, 4, and 5 are not necessary. It looks like more tutorial than a research paper. These are the main preprocessing steps of a photogrammetric product assessment.

• Figures 2, 3, 4, and 5 have been removed from the text

Page 9: In tables 3 and 4, two digits are enough after the comma.

• It has been changed in the tables

 In Table 4: write what Sx and S2 are in the caption.

• It has been added below the table

Figures 9 and 10: write the titles of the axes.

• Axis names have been added in the image description

Table 6: in the caption of the table, write the long version of the abbreviations.

• longer names of abbreviations have been added in the table name

Discussion is limited, expand it considering the previous studies which are mentioned in the introduction.

• the discussion has been expanded

Round 2

Reviewer 2 Report

In the abstract, I would suggest you remove the elements in brackets (MD, ...) and (ABCD..). 

Line 128 "for research purposes" can you delete those words?

Line 153, can you explain what snags means?

you are comparing the terrestrial approach with the image interpretation approach if I understand correctly. Would it be better to call it 'ground data' and could you add some explanation of how that piece was done?

Writing in general could be improved, for example shortened.

Author Response

Dear Reviewer,

thank you for your suggestions that contribute to the improvement of the article. Accordingly, changes were made to the text:

• In the abstract, I would suggest you remove the elements in brackets (MD, ...) and (ABCD..). 

               -  deleted from the abstract

• Line 128 "for research purposes" can you delete those words?

               - deleted from the text

• Line 153, can you explain what snags means?

               - In forest ecology, a snag refers to a standing, dead or dying tree.

• you are comparing the terrestrial approach with the image interpretation approach if I understand correctly. Would it be better to call it 'ground data' and could you add some explanation of how that piece was done?

            - The assessment of tree condition, on the ground, in the transnational network is conducted according to European-wide, harmonized methods described in the ICP Forests.  Regular national calibration trainings of the survey teams and international cross-comparison courses (ICCs) ensure the quality of the data and comparability across the participating countries. Defoliation is the key parameter of tree condition within forest monitoring describing a loss of needles or leaves in the assessable crown compared to a local reference tree in the field or an absolute, fully foliated reference tree from a photo guide. Defoliation is estimated in ranging from 0% (no defoliation) to 100% (dead tree). 

Reviewer 3 Report

The new version of the paper is improved with the suggestions. However, the discussion part is still limited. It should mention the contribution of the study, similarities, and differences, considering the previous studies with relevant citations.

Author Response

Dear Reviewer,

thank you for your suggestions that help improve the article. Consequently, the discussion chapter has been expanded (marked in the text).