Urban Above-Ground Biomass Estimation Using GEDI Laser Data and Optical Remote Sensing Images
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors1. Please mark the line number of the article when submitting;
2. In the results section (1) of the Abstract section, the description of numbers in this paragraph does not correspond to the content of Table 4 in the text. Please check carefully.
3. In the section describing research results in the abstract, “(3) the” should be changed to “(3) The”.
4. The abstract section requires significant revisions, and you can consider the following framework as a reference: background introduction, identification of research gap, the problem you aim to resolve in this research, main methods used, results, conclusion, and implications for future work. The current abstract lacks logical coherence, does not sufficiently summarize the main research findings, and omits a clear discussion of the conclusions.
5. In the abstract section and throughout the main text, the term "biomass" has been used repeatedly. It is important to note that AGB refers to “Aboveground Biomass”. When AGB is first mentioned in the article, its full name should be provided, and subsequently, the abbreviation AGB can be used. The entire document should maintain consistency in this regard. Using "biomass" to refer to AGB is inaccurate; please revise the text accordingly.
6. In the Introduction section, there should be a space after the number "1." in the heading. There are also issues with the numbering of headings in other sections. Please revise throughout the document.
7. In the fourth line of the Introduction section, "increase surface runoff" should be "reduce surface runoff".
8. On lines 6-8 of the second page, the content following "For example" describes two different research methods used by two papers. The sentence should end with "respectively." Otherwise, it may lead to the misunderstanding that both research methods were used in the same paper co-authored by two people.
9. In section 2.1, it would be better to change "the" to "an" in the tenth line of the first paragraph, because Xuzhou is not the only eco-livable city in China.
10. Can the sentence structure of the subheading 2.2 be consistent with 2.3? For example: "...imagery/data" or "...imagery/data of..."?
11. In the third line of the first paragraph of section 2.2, "25-meter" is used to describe the footprint diameter. Adding "diameter" would make it more accurate. How can it be described more precisely?
12. In lines 6-7 of the first paragraph of section 2.2, it should be "Two of the lasers" emitting one beam each, rather than together "emitting one beam". Therefore, it should be changed to "each emitting one beam".
13. In the first line of page 4, should "future carbon forests" actually be "future forests"?
14. On the first line of the second paragraph on page 4, use "the L1B data" instead of "the L1B level data", because L1B is already an abbreviation for Level 1B.
15. In the last line of the second paragraph on page 4, it mentions “Fig. 1. A”, but Fig.1 consists of subfigures (a) and (b). The figure descriptions should correspond. Is this referring to Fig.1.(b)?
16. In the sixth line from the bottom of the last paragraph on page 5, it mentions "low vegetation", while the caption of Figure 5 describes it as "shorter vegetation". These terms should refer to the same content, right? It would be better to maintain consistency throughout the text.
17. In the caption of Figure 2, after the semicolon, capitalization should only be used for proper nouns and the beginning of sentences. Should "measurement" be changed to the plural form "measurements"? Please pay attention to capitalization.
18. For Figure 3, please improve the caption by removing the word "maps"; add a legend to explain the meaning of the different styles of boxes and lines in the figure. Avoid having lines completely overlap between different frames. It would be better to optimize this flowchart to make it clearer and more understandable.
19. For the title of section 3.2, can it be made consistent with the sentence structure of the 3.1 subheading by changing it to: "Feature Extraction from ……"? Also, please pay attention to the consistency of capitalization for the first letter of the main words in each subheading.
20. On the fourth line of page 9, please maintain consistency between the text and the figure, as the figure shows "Unvegetated area". Also, the term "non-urban green space" seems to refer to green spaces found in non-urban areas, which is clearly not in line with the intended meaning in the text.
21. In Figure 5, please ensure consistency in the capitalization of the first letter of important words in the caption.
22. In Table 2, should it be "window size" in singular form, as it refers to the size of a single window? If GLCM appears for the first time in the text, an explanation should be provided, specifying its full name. Additionally, it is essential to clarify the following aspects of the data processing procedure: 1. What is the gray level of the image? 2. What is the moving step length of the sliding window? 3. What angle is set for the calculation? 4. Where do these formulas come from? It is recommended to add relevant references. In the final note, the description seems to be incorrect. According to existing literature, Pij appears to represent the probability of a certain gray level occurring, while N appears to represent the number of gray levels. Please carefully review the relevant literature to ensure the accuracy of this section and provide references for the method's origin.
23. In section 3.3, the first sentence of the last paragraph, would it be better to specify the spatial resolution of the newly established grid?
24. 3.4 section, in the first paragraph, lines 3-4, regarding the phrase "on a single wood basis", please pay attention to the language usage. Is "on an individual tree basis" a more commonly used expression in this field?
25. 3.4 section, in the first paragraph, the term "anisotropic growth equations" and the title of Table 3 "Allometric growth equation", as well as the phrase "heterozygous growth equation" in the first paragraph of section 4.3.2, part 2., line 2, are these referring to the same content? These seem to be three different concepts; please unify the expressions and describe them accurately. Should it be referring to the "Allometric growth equation"?
26. In Table 3, some of the references for the formulas are missing. Please add the missing references.
27. In section 4.1, please revise the sentence in lines 3-5 of the first paragraph to make it easier to understand.
28. In section 4.1, the phrase "ranging from 17m to 56m" in lines 6-7 of the first paragraph might be more rigorous by adding the word "mainly", as not every tree crown height is strictly within this range. The same applies to the later phrase "ranging from 0 to 12 m". Please pay attention to the accuracy of word usage.
29. In section 4.1, the phrase "which corresponds to the forest distribution area (Fig. 16)" in line 7 of the first paragraph, is it trying to express a positive correlation between canopy height and forest distribution area? The statement could be more specific. If Fig. 16 is mentioned here, it should also appear here, or the sentence and Fig. 16 can be placed together in the later discussion. In any case, under normal circumstances, a figure should appear when it is mentioned for the first time.
30. For Figure 6, please try to make the image larger and clearer, as it is currently difficult to see. The same applies to other figures. The word "inversion" should be added to the figure title to make it complete; In Figure 6, the classification of canopy height for different seasons should be kept consistent, so that they can be compared and analyzed with each other. The same applies to Figures 9 and 12.
31. For Figure 7, the word "inversion" should be added to the figure title to make it complete.
32. For Figure 9, please supplement the title to make it complete, as it is missing the keyword "inversion". The complete title should still convey the meaning of the illustrated content to the reader when separated from the main text; it would be better if the sentence structure is consistent with that of Figure 12.
33. Figure 9a and Figure 12a have already appeared in the result section, haven't they? There is no need to repeat them here; just mention the figure numbers in the main text; Are the “remote sensing images” mentioned here and the “optical images” in Figure 9(a) referring to the same content? If they are completely the same, the wording should be kept consistent, even throughout the entire article.
34. In section 4.3.2, adding a fourth-level heading would make the article structure clearer. However, the content of parts 1 and 2 does not completely distinguish between "using GEDI joint remote sensing optical images" and "using optical images", especially since the figures are placed together. You may want to reconsider the structure of this section to make it clearer, or you can consider not using a fourth-level heading.
35. In section 4.3.2, part one, first paragraph, fourth line, "quadratic term function" and "quadratic function" do not convey the same meaning; be careful with the accuracy of word choice. It should be "quadratic function" in this context, right?
36. For Figure 10, ensure the completeness of the caption; consider revising it to something like "Comparison of Four Fitting Functions for the Relationship between Max Canopy Height and AGB." The content in the figure and text should be consistent; the number of decimal places for R2 and RMSE should match those in the main text.
37. On page 14, in the first line of the first paragraph, the term "two functions" is mentioned. Does this refer to the power function and quadratic function mentioned earlier in the text? It should be specified by adding "the" or "the above" to help readers clearly understand which "two functions" are being referred to in this context.
38. On page 14, in the fourth line of the first paragraph, the term "AGB" is mentioned. Does this refer to "AGB prediction"? Please be accurate with your wording. Additionally, were all subsequent calculations regarding AGB based on the power function? Please clarify this point.
39. In Figure 11, the text within the image is unclear.
40. On page 14, in the last paragraph, the term "single wood" appears in the fourth line from the bottom. It would be more accurate to change "wood" to "tree."
41. In Figure 12, the month for this image is not specified. Please add the missing information.
42. The Discussion section, particularly sections 5.2 and 5.3, needs significant revisions, including improvements in language and illustrations. The interpretation of research results should be more convincing. Please discuss in conjunction with similar studies, and make the content more organized and clear.
43. In Figure 13, what does the vertical axis specifically represent? Is it the correlation coefficient? Should "feature" in the horizontal axis be in plural form? It is better to keep the information in the figure, figure caption, and the main text consistent. For example, "feature" in the figure and "predictor variables" in the caption should refer to the same content, right?
44. In Figure 14, the water body part should be marked separately, as there is no canopy height in the water body. It should be clarified in both the figure and the text whether "the difference" refers to "the canopy height derived from GEDI joint optical image inversion" minus "the canopy height derived from optical image inversion." This should be explicitly stated in the article.
45. The content in section 5.2 needs major revisions, as the current text and Table 4 are very confusing. There are sudden additions of new forest figures, followed by discussions on urban forests, but the specific areas of urban forests are unclear. The content needs to be more organized and should clearly discuss the main points, ensuring tight logic between contexts and prominent viewpoints. It is best to discuss this in conjunction with other relevant studies. The language in this section also has significant issues and requires further modifications.
46. Table 4 has a disorganized content and is difficult to understand. Please reorganize and arrange it; Table 4 should appear immediately after the text discussing it.
47. Table 4 is missing some information. The information about the proportion of AGB for different vegetation types mentioned in the first paragraph of section 5.2 is not found in the related figures and text. The table only shows the unit area AGB of different vegetation types and their AGB distribution ratio.
48. In the third line of the first paragraph of section 5.2, "This is because..." needs to be reorganized and clarified. It is apparent that this is not an explanation for why "the ratio of AGB distribution in shorter vegetation area is the least for vegetated areas" in the previous text, but rather for the subsequent content. This is a case of logical confusion.
Does "the low vegetation area" refer to "shorter vegetation area"? It is important to use consistent terminology throughout the text to avoid confusion.
What does "The coniferous forests are all distributed in urban forests, so coniferous forests have the larger ratio of AGB distribution" mean? It is difficult to understand, and what are urban forests and non-urban forests? Has this study delineated urban forest areas?
Table 4 only shows the unit area AGB of different vegetation types, and Figure 15 only shows the AGB proportion of different unit area AGB for each vegetation type. Where is the total AGB and its proportion for different vegetation types? Please provide this information.
Does the "forest" in Figure 16 include shorter vegetation, broadleaf forest, and coniferous forest? How is it different from Figure 5a? Does it exclude the grass part of shorter vegetation? Please clarify.
The text mentions that "Fig. 15a is basically in the range of 10 Mg/ha~40 Mg/ha", but there are also many proportions in the 40-70 range. Why are they ignored?
How was it determined that "The biomass range of urban forest areas is significantly higher than that of surrounding areas such as sidewalks and neighborhood greenery"? Which specific areas are considered urban forest areas? Please clarify in the figure.
Can impervious surfaces (e.g., roads, buildings, etc.) be displayed in the figure?
The important words in all figure and table names in Figure 5 should have consistent capitalization.
Figure 5 uses the term "three typical urban green space types", Table 4 uses "different landcovers", and Figure 15 uses "different vegetated areas". It is recommended to use consistent terminology throughout the text.
49. Can we directly calculate the AGB of different vegetation types in different seasons in section 5.3? What do other studies say about the seasonal variation in vegetation AGB?
The organization of Table 4 is confusing, as it does not clearly indicate whether the Average AGB during Oct.-Dec. is referring to shorter vegetation or all vegetation types. The current structure of the table is not logical, and if necessary, it could be split into two separate tables for better clarity.
Considering the seasonal patterns of vegetation AGB, it is expected that during the winter months (1-3), when plants are dormant and undergoing leaf shedding, the AGB should be at its lowest. As the temperature warms up during spring (4-6), vegetation begins to grow, and the AGB should be higher compared to the winter months. In the summer months (7-9), which are the peak growing season, vegetation should be lush and thriving, resulting in the highest AGB values, at least higher than those in the winter and spring months. The results presented in Table 4 are highly inconsistent with these expected patterns, which is not reasonable. The discussion section of this study does not provide a convincing explanation for these inconsistencies. Further analysis, incorporating similar studies, is needed to understand the underlying reasons for these discrepancies.
50. Line 4 of the first paragraph of Part 5.3. Isn’t the result analyzed here not the GEDI joint optical image but the only remote sensing imagery that was previously judged to be inaccurate? why is that? Secondly, shouldn’t the canopy height measured from remote sensing images be higher when the branches and leaves are more lush? Why is it said to be underestimated here? If we follow the logic here, how can we explain October-December? Moreover, trees grow slowly, and the canopy height changes should not be obvious throughout the year. Why are the changes here so obvious? Is this related to other factors such as crown width?
51. The water area in Figure 17 should be marked separately; it is recommended to classify the changing values, for example, into: unchanged, (significantly) more or less. Reduce the number of categories and use more distinguishing colors to represent them. For example, use warm colors for smaller areas and cold colors for larger areas to make it easier for readers to distinguish. The same suggestion also applies to Figure 14.
52. Are the statistical results in Table 4 derived from the GEDI joint optical image inversion results? Please explain. Can you compare and analyze the GEDI joint optical image inversion results and optical image inversion results in different seasons?
53. The conclusion section needs major revision. Many contents in it are inconsistent with the main text. It is recommended to reorganize the conclusion section. The existing three conclusions are not sufficient. Note that these conclusions are a summary of the content of the article. You cannot suddenly bring up content that has not appeared in the article. If there is new content that you want to emphasize, it is recommended to fully discuss it in the discussion section and then summarize it in the conclusion section. For example, content about the types of trees in cities.
54. In the Conclusion section, line 6 of the first paragraph, rewrite this sentence to increase its readability so that readers understand the meaning of this sentence; in line 7, "anisotropic growth equation" should be changed to "allometric growth equation", right?
In the second paragraph, "cities" in the last line, how are the spatial boundaries of cities in this study divided? This question should be answered in the first part of the article. In this study, Xuzhou City is divided by administrative division boundaries, which does not seem to express the same concept as cities here, right? I feel that the cities here specifically refer to "Urban Green Space", that is, "Green space within built-up areas." How to divide this concept? The two concepts cannot be confused, otherwise misunderstandings will occur.
55. In the Conclusion section, (2) part, this study has proven that the accuracy of using remote sensing image to extract the vegetation canopy height is not high. In this case, the focus should be on the method of combining GEDI and remote sensing images, and why the method of combining GEDI and remote sensing images is better than only using remote sensing images, right?
56. In the Conclusion section, (3) part, lines 5-7, the data description is inconsistent with the text content in Table 4 and part 5.3. In addition, part 5.3 says that the AGB of Oct.-Dec. is an overestimate, but here it says underestimated, which is inconsistent.
Comments for author File: 
Comments.pdf
Some sentences are difficult to understand, some are repetitive and cumbersome, and many words are inaccurate. Please revise them carefully.
Author Response
"Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors submitted a well written and an interesting manuscript dealing with the estimation of the above ground biomass from remote sensed imageries. The results are well represented how the authors should provide some additional information in the manuscript. Below are some comments and suggestions to improve the overall quality of the manuscript.
Information provided on the table 1 are not comprehensible. You mentioned that you used 2 optical remote sensing images: Sentinel 2 and Landsat 8, you should provide the exact date/time of acquisition, spatial resolution and spectral resolution (Spectral band used) for each image used for this study. Such information would help readers understand the characteristics of the fused images and bio-physical features they could extract on them. For the DEM from Shuttle Radar Topographic Mission, I would suggest you using the one with spatial resolution of 30 meters.
For the equation 1, indicating the estimation of the canopy height it would be interesting to include some references of the previous studies conducted using GEDI waveform data.
On the Table 2, the authors could replace the spectral indices by Spectral bands.
On the section of the results, it would be interesting to make a comparison for the results obtained using Sentinel 2 and the one obtained using Landsat 8. Such comparison would help readers explore the effect of characteristics (Spatial and spectral resolutions) these images. In addition, it is not clear from the presented methodology, how the authors integrated information of 5 land cover in the models as they stated in the conclusion.
Comments on the Quality of English LanguageMinor editing of English language are required
Author Response
"Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThis paper examined a remote sensing approach for the estimation of AGB in China, which is very interesting but needs modification regarding the accuracy validation for AGB estimation. Specific comments are as follows.
*Figures 1, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, and 17. Letters are not well visible. More precise and high-resolution images are required.
*Figures 10 and 11. About ten samples were used for the AGB estimation, which did not seem sufficient to evaluate the models' performance.
Author Response
"Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 4 Report
Comments and Suggestions for AuthorsAccording to the authors, “This study proposes a method for estimating the vegetation heights by fusing GEDI laser observations with features extracted from optical remote sensing images… using Random Forest (RF) to obtain the vegetation canopy heights in all vegetated areas, thus estimating the AGB in urbanized areas.” The topic and the developed methodology are of interest to a wide readership.
The study succeeded in achieving its aim with easy to follow write up. However, there are few incidents where it is seems that the choice of words or the grammar may not be correct. The manuscript would benefit from another round of editing to maintain consistency in the writing style as well as the flow. Below are my comments on the methodology and on some writing mishaps.
Methodology:
Although it is indicated on the flowchart in Figure 3, there is no details related to the generation of the “canopy height derived from optical image inversion” (first mentioned on page 13). The authors need to provide details on the method used in this task, as well as the difference between this one and the one generated from GEDI and optical images combined.
Write-up and typographical errors
If possible, change “Miles” to “Km” in all maps (Figures 1, 5, 6, 7, 9, 12, 14, 16, and 17).
Page 5, last paragraph, 1st line: change “titled” to “tilted”.
Page 9, 1st paragraph, 2nd line: insert “classification method” after “Support Vector Machine”.
Page 9, Table 2: include/cite sources/references for all equations
Page 10, header for section 3.4: insert “field-based” before AGB. In general, it would be more informative if you would call each AGB with a distinctive name/abbreviation, e.g. gAGB for the one from GEDI, sAGB for the one from satellites, and fAGB for the one based on field measurements.
Page 11: fix what it seems something missing or wrong grammar in the 2nd sentence that starts with “Since GEDI footprints have…”
Page 13, caption of Figure 8 (b): change the word “united” into “joint” since the later is the term used throughout the manuscript. Although, “GEDI joint remote sensing image” still looks weird.
Page 15: on the horizontal axis of figure 13, “band5” appears twice, so is “band4” which make impossible to separate between Landsat and Sentinel bands. Adding a prefix of “L” for Landsat, and “S” for Sentinel may ease the confusion.
Comments on the Quality of English LanguageThere are few incidents where it is seems that the choice of words or the grammar may not be correct. The manuscript would benefit from another round of (minor) editing to maintain consistency in the writing style as well as the flow.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 5 Report
Comments and Suggestions for AuthorsThis study by Zhao et al. proposes a method to estimate above-ground biomass (AGB) in urban areas using NASA's Global Ecosystem Dynamics Investigation (GEDI) mission data combined with features extracted from optical remote sensing images. By leveraging Random Forest (RF) to correlate GEDI's discrete vegetation height observations with image features, the study aims to estimate vegetation canopy heights and subsequently AGB in urbanized areas. The method was tested in Xuzhou, China, using GEDI observations and Sentinel-2/Landsat-8 images, and validated against field observations. Results showed biomass estimates ranging from 35.40 to 47.40 Mg/ha in different vegetation zones, with an overall estimate of 38.07 Mg/ha from April to June in Xuzhou. The integration of GEDI data and optical remote sensing images yielded higher AGB estimation accuracy (R2=0.75) compared to using remote sensing images alone (R2=0.45).
Overall the manuscript is well written However I have the following comments:
Introduction
'Considering that remote sensing imagery can obtain the complete spatial distribution of vegetation in the region, it is possible to establish the correlation between the features of vegetation extracted from the remote sensing imagery and height features of vegetation derived from the spaceborne LiDAR, and thus to estimate more accurate canopy height and AGB of vegetation in urban areas by combining spaceborne LiDAR data with remote sensing imagery. This is the idea behind the study but this needs to be better highlighted, so linked to the next paragraph.
The presentation of the manuscript sections should be deleted.
This is the idea behind the study but this needs to be better highlighted, so linked to the next paragraph.
The presentation of the manuscript sections should be deleted.
The whole section needs to be rewritten because there are too many details. Concentrate on the basic ideas by which you want to introduce the reader to the topic.
However, the instructions for authors of this journal should be read carefully and corrections should be made accordingly.
. Study Area and Material
'Xuzhou is a nationally important comprehensive transportation hub with a large population, and it is the ecologically livable city in China' what is the relevance of this?
GEDI is described in detail. Summarize in describing how you used GEDI.
Results
Figures 6 and 7 and even 5 and 9 do not look very good. They need to be enlarged.
Figure 10 can't be read very well either.
Discussion
Where are the discussions. The whole section needs to be reworded. Read carefully how this section is composed and reformulate it.
Conclusion
This section needs to be more concise. Avoid repetition.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for Authors1. Please reduce the word count of the abstract as much as possible, preferably to no more than 300 words.
2. Reconsider the conclusion in point (3) of the abstract. According to existing research, the meaning represented by the index of Gini seems to be the opposite of what is stated in this paper. It should be that the smaller the index of Gini, the more important the indicator.
3. In Table 1, the first column Landsat-8 and Sentinel-2 should only appear once each, instead of repeating multiple times.
4. On line 193, the first letter of "Fieldwork" should be lowercase.
5. 4.1 Ensure consistent capitalization in subheadings throughout the article. Change "4.1 Vegetation Canopy Heights Mappings" and "4.3 Comparison and Validation" to "4.1 Vegetation canopy heights mappings" and "4.3 Comparison and validation," respectively.
6. Lines 462-478 seem to contain a serious error. Please carefully review related literature to ensure that the article does not contain basic errors. Refer to explanations of the index of Gini in the related literature. Based on existing research, the index of Gini seems to follow the principle of being smaller for greater importance, so this entire section, including relevant parts of the abstract, needs to be corrected. (Existing literature indicates that when evaluating the importance of various indicators in decision trees, a smaller Gini coefficient represents a better outcome, meaning that the importance of the indicator is higher. This is contrary to the current situation in the text. Please verify this information.)
7. In Table 4, the data for Total AGB should be rounded to two decimal places.
8. In Figure 15, the capitalization of "Broadleaf Forest" and "Coniferous Forest" in the titles of (b) and (c) is not necessary, as they are not proper nouns.
9. Reconfirm the correct meaning of the Gini index in lines 519-523. There is a high probability that the analysis here is reversed and needs to be corrected.
Comments on the Quality of English LanguagePlease carefully read and check for any errors.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsNo further comments
Comments on the Quality of English LanguageMinor english language editing are required
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe canopy height was well modeled. However, the predicted AGB was not sufficiently optimized using 10 to 20 samples. This should be described in more detail in section 4.3.2. Also, the shortage of AGB measurements should be discussed in depth in Section 5. A new subsection 5.4 for the discussion of the limitation will be required.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 5 Report
Comments and Suggestions for AuthorsI should mention that the authors have taken into account the comments made and the manuscript has been improved.
However, there remains a big problem in the Discussion section. As I said before, there are no actual discussions. Just results presented in detail. There are only two bibliographic references in this whole section.
So, move the results to the appropriate section and add more discussions, with the appropriate bibliographic references.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
