Near-Earth Remote Sensing Images Used to Determine the Phenological Characteristics of the Canopy of Populus tomentosa B301 under Three Methods of Irrigation

Round 1

Reviewer 1 Report

The phenology can well reflect the climate change and was widely concerned by researchers. The authors investigated the phenological characteristics under different irrigation situations in artificial forest in China. The research is of great interesting and the results are reasonable.

 Major comments:

1.      In the experiment, the 5^th preset point is near the forest edge, so in figure 5, the background (crop land?) can be seen clearly in the preset point 5. I think the background will affect the result, the authors should analyze the effect and discuss in the discussion section.

2.      The discussion section is not like a discussion, some references can be in the introduction, and subtitles are needed for each point you discussed.

 

Minor comments:

1.      Figure 3 the second and the third picture are wrong. The names are misallocated.

2.      What is the average tree height? How far does the camera from the canopy?

3.      In figure 6, five pictures are from different scenes, the target and size are different. They should be of the same scene.

4.      Figure2, 9 are very hard to read, they are very vague. Most of the figures should be redrawed, and put high resolution pictures in the paper.

5.      Line 313-314, the abbreviations are not written properly, the full name should be in the main context and the abbreviation in the bracket.

6.      Line 548, the conclusion “It indirectly infers that BIFI has more advantages than DIFI,” contradicts with former statements.

Author Response

Response to Reviewer 1 Comments

 

 Major comments:

 

Point 1: In the experiment, the 5th preset point is near the forest edge, so in figure 5, the background (crop land?) can be seen clearly in the preset point 5. I think the background will affect the result, the authors should analyze the effect and discuss in the discussion section.

 

Response 1: We gratefully thank for your valuable time and effort in reviewing our manuscript! And we totally understand your concerns. As you said, The fifth preset point is close to the forest edge, and the background will affect the results. Thank you for your suggestion. At that time, due to the installation time before crop planting, we did not consider it comprehensively. According to your suggestion, We revised and explained 2.5 in the manuscript. In addition, changes made to the manuscript have been marked with yellow labels to highlight. Thank you again for your careful examination.

According to your suggestion, we made the following corrections in the manuscript:

Due to the late planting time of crops in the farmland near the research base, the farmland crops have little impact on the early stage of image acquisition. Secondly, the distance between the near earth remote sensing equipment and the crops in the crop field is relatively long and the height difference is relatively large. When the vegetation and crops grow vigorously, a little error may occur, but the overall impact will not be too great. Considering this problem after image acquisition, the region of interest of preset point 5 is placed in the center, away from the edge of the crop land, so as to minimize the error of the external environment on the extracted vegetation index and will not affect the overall research results.

 

Point 2: The discussion section is not like a discussion, some references can be in the introduction, and subtitles are needed for each point you discussed.

 

Response 2: We gratefully appreciate for your valuable suggestion. Your suggestions are of great help to improve the readability and quality of the article . We have modified the discussion of the manuscript and marked it with a yellow cursor to highlight it. We hope our work can promote a better understanding of the manuscript. Thank you again for your careful examination.

 

Minor comments:

 

Point 1: Figure 3 the second and the third picture are wrong. The names are misallocated.

 

Response 1: We gratefully appreciate for your valuable suggestion. Your suggestions are of great help to improve the readability and quality of the article. We have made corresponding revisions in the article based on your comments, Changes made to the manuscript have been marked with yellow labels to highlight them.We hope our work can promote better understanding of the manuscript. Thanks again for your valuable comment.

 

Point 2: What is the average tree height? How far does the camera from the canopy?

Response 2: We gratefully appreciate for your valuable suggestion. Your suggestions are of great help to improve the readability and quality of the article. The average height of Populus tomentosa B301 in our experimental base is 9-15 meters. Due to different shooting positions, the direct overhead viewing distance from the near earth remote sensing equipment to the tree canopy is different. Visually check that the distance from preset point 3 is about 20m, and the distance from preset point 1 and preset point 5 is about 12m.We hope our work can promote better understanding of the manuscript. Thanks again for your valuable comment.

Point 3:  In figure 6, five pictures are from different scenes, the target and size are different. They should be of the same scene..

 

Response 3: We gratefully appreciate for your valuable suggestion. Your suggestions are of great help to improve the readability and quality of the article. At that time, in order to more clearly express the obvious changes in the fine characteristics of vegetation throughout the year, scenes at different locations were selected to highlight the effect of vegetation growth changes. According to your suggestion, we have modified the "select a scene at the same location" in the manuscript. We have changed the scene in Figure 6 to the same scene. We find that the effect will be better at this time. Thank you for your suggestion. Changes made to the manuscript have been marked with yellow labels to highlight them.

Point 4:  Figure2, 9 are very hard to read, they are very vague. Most of the figures should be redrawed, and put high resolution pictures in the paper.

 

Response 4: We gratefully appreciate for your valuable suggestion. Your suggestions are of great help to improve the readability and quality of the article. We have modified figures 2 and 9 in the manuscript and replaced them with high-definition images. The modifications made in the manuscript have been marked with yellow labels to highlight them. Thanks again for your valuable comment.

 

Point 5:  Line 313-314, the abbreviations are not written properly, the full name should be in the main context and the abbreviation in the bracket.

 

Response 5: We gratefully appreciate for your valuable suggestion. Your suggestions are of great help to improve the readability and quality of the article. We have made corresponding revisions in the article based on your comments. Changes made to the manuscript have been marked with yellow labels to highlight. Thanks again for your valuable comment.

 

Point 6:  Line 548, the conclusion “It indirectly infers that BIFI has more advantages than DIFI,” contradicts with former statements..

 

Response 6: We gratefully appreciate for your valuable suggestion. Your suggestions are of great help to improve the readability and quality of the article. We have made corresponding revisions in the article based on your comments. Has been marked with a yellow cursor. we hope our work can promote better understanding of the manuscript. Thanks again for your valuable comment.

 

Author Response File: Author Response.docx

Reviewer 2 Report

Comments are in the attached file.

Comments for author File: Comments.pdf

Author Response

Response to Reviewer 2 Comments

 

Point 1: I suggest author to improve the abstract. For example, Line 23-32 should be further refined. Line 35-36: I don’t think this statement was supported by this draft.

 

Response 1: We gratefully appreciate for your valuable suggestion. Your suggestions are of great help to improve the readability and quality of the article. According to your suggestion, We have modified the abstract ( line 23-32) of the manuscript and marked it with a yellow cursor to highlight it. Secondly, we delete ( line 35-36). We hope our work can promote a better understanding of the manuscript. Thank you again for your careful examination.

 

Point 2: Introduction. I suggest the authors to add an analysis on how other researchers studied the impact of irrigation on the phenology instead of claiming that “There are few researchers ….” (Line 101-103). This can’t become an assumption of this paper. I suggest authors to list and analyze the research status.  

 

Response 2: We gratefully appreciate for your valuable suggestion. Your suggestions are of great help to improve the readability and quality of the article. According to your suggestion, we deleted the (Line 101-103) of the manuscript and added the research status of the impact of irrigation on phenology, which is marked with a yellow cursor to highlight. We hope our work can promote a better understanding of the manuscript. Thank you again for your careful examination.

 

Point 3: Line 224: this draft used mean value of 1 day to calculate the vegetation index. Why do you use “average” instead of “maximum” value? Also, as the date goes from spring to summer, the brightness of an image in spring, for example, at 5 pm, may be darker than an image in the summer. This may become a leading factor affecting the vegetation index. Why not use the images between sunrise and sunset, temporally?

 

Response 3: Thank you for your question. The question you mentioned is very good. Why use the average value instead of the maximum value? It is because the difference in the sunlight time of the whole year and the light intensity of the day will cause large errors, and the average value can reduce the error value. Secondly, why not use the maximum value? Because the time of the maximum sunshine in summer and winter is different, the illumination brightness at the same time of the year cannot be guaranteed. For example, the 5:00 illumination image in summer can be viewed, and the 5:00 illumination image in autumn and winter has been blurred. Similarly, the maximum value is not considered for the images in the morning and noon because the sun illumination angle will also cause the problem of excessive illumination reflectivity. Finally, by consulting relevant data, the annual phenological monitoring in the literature uses the average value. However, the next step is to try the difference between the maximum value and the average value. We hope our work can promote better understanding of the manuscript. Thanks again for your valuable comment.

 

Point 4: Figure 8. I suggest you make the color of curve at a present point consistent among sub-figures, which would improve the readability. The same strategy should be applied to all other figures.

 

Response 4: We gratefully appreciate for your valuable suggestion. Your suggestions are of great help to improve the readability and quality of the article. Because all the schematic diagrams in Fig. 8 are put together, the pixels of the main diagram and the sub diagram are compressed and different. Therefore, according to your proposal, we put figure 8 in the manuscript separately, and the effect will be better at this time. We have modified figure 8 of the manuscript and marked it with a yellow cursor to highlight it. Thank you again for your careful examination. Thank you again for your careful examination

 

Point 5: Figure 7(a), what’s the purpose of annual rainfall?

 

Response 5: Thank you for your valuable questions. The purpose of the annual rainfall in Figure 7a is to highlight that the annual rainfall season in this area is after June 29. Secondly, it also wants to show that the early rainfall is low, which can be compared with figure 7b (CK). Thank you for your careful examination.

 

Point 6: Line 365-384: I suggest you add table to show the difference in values like the amplitude and change of some critical date.

 

Response 6: We gratefully appreciate for your valuable suggestion. Your suggestions are of great help to improve the readability and quality of the article. According to your suggestion, We added the difference in values like the amplitude and change of some critical date  to the  tables in the manuscript (lines 365-384), which is marked with a yellow cursor to highlight. We hope our work can promote a better understanding of the manuscript. Thank you again for your careful examination.

 

Point 7: Figure 10: is there a way to perform a statistical test to show the difference in the GCC curve caused by irrigation? You need to show the difference is significant.

 

Response 7: We gratefully appreciate for your valuable suggestion. Your suggestions are of great help to improve the readability and quality of the article.The vegetation indexes of preset point 1, preset point 3 and preset point 5 were compared and analyzed by using one-way analysis of variance (ANOVA) in SPSS method, and tested by LSD, S-N-K and Duncan methods. The results show that there are significant differences among the three irrigation methods, which will lead to the difference of GCC curve. The specific analysis results are as follows:

Descriptives
vegetation index
Preset	N	Mean value	Std. Deviation	Std. Error	95% Confidence Interval for Mean		Minimum	Maximum
					Lower Bound	Upper Bound
1.00	95	0.3948688	0.02425112	0.00248811	0.3899286	0.3998090	0.33606	0.45514
3.00	95	0.4108927	0.02973966	0.00305122	0.4048344	0.4169510	0.33920	0.47271
5.00	95	0.4044397	0.02938133	0.00301446	0.3984544	0.4104249	0.34099	0.46707
Total	285	0.4034004	0.02857643	0.00169272	0.4000685	0.4067323	0.33606	0.47271

 

Test of Homogeneity of Variance
vegetation index
Levene Statisic	df1	df2	Sig.
3.898	2	282	0.021

Analysis:It can be seen from the table that it is used to test whether there is significant difference in the variance of experimental samples at preset points 1, 3 and 5. It can be seen from the results that the F statistic of Levene variance homogeneity test is 3.898, and the corresponding p value under the current free condition is 0.021. On the premise that the given significance level is 0.05, the variance homogeneity test is passed, that is, the change of GCC curve comes from different irrigation methods, meeting the requirements of variance analysis.

ANOVA
vegetation index
			Sum of Squares	df	Mean Square	F	Sig.
Between Groups	（Combined）		0.012	2	0.006	7.931	0.000
	Linear Term	contrast	0.004	1	0.004	5.588	0.019
		Deviation	0.008	1	0.008	10.274	0.002
Within Groups			0.220	282	0.001
Total			0.232	284

 

Multiple Comparisons
Dependent Variable: vegetation index
	(I) Preset	(J) Preset	Mean Difference (I-J)	Std. Error	Sig.	95%Confidence Interval
						Lower Bound	Upper Bound
LSD	1.00	3.00	-.01602390*	0.00404867	0.000	-.0239934	-.0080544
		5.00	-.00957085*	0.00404867	0.019	-.0175403	-.0016014
	3.00	1.00	0.01602390*	0.00404867	0.000	.0080544	.0239934
		5.00	0.00645305	0.00404867	0.112	-.0015164	.0144225
	5.00	1.00	0.00957085*	0.00404867	0.019	.0016014	.0175403
		3.00	-.00645305	0.00404867	0.112	-.0144225	.0015164

 

*. The mean difference is significant at the 0.05 level. The output result of LSD method actually requires comparing the average value of each group with a reference group. SPSS assumes that each irrigation method may become a reference, so that other groups can be compared with the reference group. The difference in mean value, standard error of difference, 95% confidence interval and P value of test between the two irrigation methods are given in the table. I refers to the reference group and j refers to the comparison group. The inspection results show that preset point 1 is different from preset point 3 and preset point 5, but there is no difference between preset point 3 and preset point 5.

Congeneric subset

vegetation index
	Preset	N	Subset for alpha=0.05
			1	2
Student-Newman-Keulsa	1.00	95	0.3948688
	5.00	95		0.4044397
	3.00	95		0.4108927
	Sig.		1.000	0.112
Duncana	1.00	95	0.3948688
	5.00	95		0.4044397
	3.00	95		0.4108927
	Sig.		1.000	.112

 

Means for groups in homogeneous subsets are displayed.

a. The harmonic mean sample size will be used = 95.000。

 

Point 8: Table 3. What’s the accuracy of these SOS, MOE, and EOS?

 

Response 8: Thank you very much for your question about table 3 What's the accuracy of the these SOS, MOE, and EOS? The SOS was taken on March 24, when Populus tomentosa B301 had sprouted. We set this time as the beginning of the vegetation growth season. As the experiment was conducted in the first year, this period is only for reference. MOE is a comparative analysis of the data of the whole year. The green reflectance reaches the highest in the period of vigorous vegetation growth, and the data extracted from the vegetation index is also the highest. Similarly, at the end of vegetation growth (EOS), the green reflectance of vegetation reaches the lowest, and the extracted vegetation index data is also the lowest. The overall result extraction accuracy is relatively good. We hope our work can promote a better understanding of the manuscript. Thank you again for your careful examination.

 

Point 9: Experiment design: There were 3 sites in your study. Although the data was captured by cameras, the data was averaged. Therefore, do you think using 3 sites’ data can confirm that precipitation/irrigation is a factor for the phenological response? Why?

 

Response 9: Thank you very much for your question. By consulting relevant literature, we found that there are many studies on the response of temperature and other influencing factors to vegetation phenology. By controlling the experimental theoretical method, we observed the relationship between the average value of daily and monthly temperature changes and vegetation phenology. The research on precipitation is basically traditional. Phenological analysis is carried out by observing rainfall and vegetation changes. At present, it has been widely used to obtain vegetation images for phenological analysis through near earth remote sensing equipment monitoring. Our precipitation and irrigation are monitored in real time through self-developed sensors. The precipitation and irrigation are digitized, which can better monitor the changes between the two. Therefore, we try to take the relationship between the water change in the experimental base and the acquisition of vegetation images as a factor of phenological response. However, the impact of climate factors on plant phenology is comprehensive. Considering the impact of other factors on plant phenology, such as CO2, O3, UV-B radiation, the change of plant phenology is more complex. We hope our work can promote a better understanding of the manuscript. Thank you again for your careful examination.

 

Point 10: Line 522: why GCC is more aligned? Which data support this?

 

Response 10: We gratefully appreciate for your valuable suggestion. Your suggestions are of great help to improve the readability and quality of the article. Because the relative greenness index (GGR) of rain fed (preset point 1) reached the peak of growth (MOE) 2 days earlier than that of difi (preset point 3) and BIFI (preset point 5), and the growth season (EOS) withered 6 days earlier; The same is true for CK (preset point 1) in green red vegetation index (grvi). The peak time (MOE) of relative greenness index (GCC) of Populus tomentosa B301 cultivated by the three methods is the same, but the difference is that the end of growth season of CK (preset point 1) is 8 days faster than difi (preset point 3) and 7 days faster than BIFI (preset point 5). In order to better reflect the differences of the three cultivation methods, we selected GCC and GEI with the same peak time. Both GCC and GEI can better reflect the growth changes of Populus tomentosa B301, but the change range of vegetation index of GCC is larger, which can be observed and analyzed more clearly. Therefore, GCC is selected as the index of vegetation index this time. We hope our work can promote a better understanding of the manuscript. Thank you again for your careful examination.

 

Point 11: Line 513-518: either provide the citations or show the supported data. Also, I don’t the content here related to your research.

 

Response 11: We gratefully appreciate for your valuable suggestion. Your suggestions are of great help to improve the readability and quality of the article . According to your suggestion, we deleted the manuscript (Line 513-518). We hope our work can promote a better understanding of the manuscript. Thank you again for your careful examination.

 

Point 12: I suggest authors to reorganize the discussion part. Line 506-513 seems to summarize the conclusions at the beginning of discussion. I don’t think conclusions should be written before any analysis. The same problem applies to other paragraph in the discussion. In addition,

 

Response 12: We gratefully appreciate for your valuable suggestion. Your suggestions are of great help to improve the readability and quality of the article . We have modified the discussion of the manuscript and marked it with a yellow cursor to highlight it. We hope our work can promote a better understanding of the manuscript. Thank you again for your careful examination.

 

Point 13: Line 562-564: are these statements your findings? or, please provide the citations.

 

Response 13: Thank you very much for your question. This statement was put forward by the author Lianxi Wang in research advances in plant meteorology and climate, and marked with a yellow cursor to highlight it. We hope our work can promote a better understanding of the manuscript.

 

Point 14: Line 487: What is LOS?

 

Response 14: We gratefully appreciate for your valuable suggestion. Your suggestions are of great help to improve the readability and quality of the article. We have made corresponding revisions in the article based on your comments, the LOS has been deleted, Has been marked with a yellow cursor. we hope our work can promote better understanding of the manuscript. Thanks again for your valuable comment.

 

Point 15: Line 597: shower

 

Response 15: We gratefully appreciate for your valuable suggestion. Your suggestions are of great help to improve the readability and quality of the article. According to your opinion, we have modified the word accordingly. Has been marked with a yellow cursor. we hope our work can promote better understanding of the manuscript. Thanks again for your valuable comment.

 

 

Author Response File: Author Response.docx

Reviewer 3 Report

The article requires only small additions and technical corrections.

 

1.         The discussion and conclusions should be extended with the issue from the title of the article "Near-earth remote sensing images used ...." - verifications of the adopted measurement methodology.

2.         The title of figure 2 needs to be improved (the current title is an explanation of the colors used); besides, the legend of the drawing is very difficult to read (even at a very high magnification of the drawing).

3.         In the description of Figure 3, a description of the individual photos should appear (a, b, c,).

4.         The correctness of the numbering of figures in the text should be verified (eg line 196: there is figure 3, and it should be figure 4, line 216 ...).

Author Response

Response to Reviewer 3 Comments

 

Point 1: The discussion and conclusions should be extended with the issue from the title of the article "Near-earth remote sensing images used ...." - verifications of the adopted measurement methodology.

 

Response 1: We gratefully appreciate for your valuable suggestion. Your suggestions are of great help to improve the readability and quality of the article. We have revised the discussion and conclusion of the manuscript accordingly. Has been marked with a yellow cursor. we hope our work can promote better understanding of the manuscript. Thanks again for your valuable comment.

 

Point 2: The title of figure 2 needs to be improved (the current title is an explanation of the colors used); besides, the legend of the drawing is very difficult to read (even at a very high magnification of the drawing).

 

Response 2: We gratefully appreciate for your valuable suggestion. Your suggestions are of great help to improve the readability and quality of the article. We replaced the high-quality Figure 2. Has been marked with a yellow cursor. we hope our work can promote better understanding of the manuscript. Thanks again for your valuable comment.

 

Point 3: In the description of Figure 3, a description of the individual photos should appear (a, b, c,).

 

Response 3: We gratefully appreciate for your valuable suggestion. Your suggestions are of great help to improve the readability and quality of the article. We have modified Figure 3 accordingly. Has been marked with a yellow cursor. we hope our work can promote better understanding of the manuscript. Thanks again for your valuable comment.

 

Point 4: The correctness of the numbering of figures in the text should be verified (eg line 196: there is figure 3, and it should be figure 4, line 216 ...).

 

Response 4: We appreciate for your valuable comment. Your suggestions are of great help to improve the readability and quality of the article. We have made corresponding modifications to figures 3 and 4 of the manuscript and checked other places. Has been marked with a yellow cursor. Thanks again for your valuable comment.

 

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

All my questions are well answered.