Plugging the Gaps in the Global PhenoCam Monitoring of Forests—The Need for a PhenoCam Network across Indian Forests

Round 1

Reviewer 1 Report

1. The use of acronyms is not consistent throughout the paper.

a) For example, in some places only the first letters are capitalized - Line 310: Leaf Area

Index (LAI).

b) But in most places, they are all lowercase – Line 11, 83-84, 91, 132, 139, 171 and so

on.

c) The same acronym has been used multiple times – Line 149, 310, 329, 332, 362.

d) If the term ‘Phenological Monitoring’ is assigned as ‘PM’ (Line 11), then use ‘PM’ every

time instead of the full term (Line 58, 73, 82 etc.).

e) Full form + acronym should be used only once and thereafter use only the acronym.

2. Line 72, Use less text inside the image. Also, if possible, increase the font size of Figure 1.

3. Line 91, Though UAV is near surface remote sensing with high spatial resolution it cannot

have the same temporal resolution as PhenoCams (hourly).

4. Line 127, The same font issue is with Figure 3. The abbreviations are already explained in

the text (Line 139), and the Image caption is sufficient to explaining each image. Thus, I

think the text inside Figure 3 is redundant. Please remove it.

5. Line 196-200, How these studies have been selected, and with what parameters or

metrics?

6. Line 201-202, I didn’t understand the logic of making Figure 4 in accordance with the IPCC

AR6 report.

7. Line 259, ‘Additional to this’ --> ‘Additionally’ or ‘In addition to this’ would be a better

phrase.

8. In Chapter 4, It would be better if you also give a number of studies for reference. It would

be easy to understand the scale of this distribution.

9. The usage of articles (‘a’ and ‘the’) needs to be improved.

10. I felt in-depth successfully implemented Indian PhenoCam case study is missing.

11. Line 447 onwards, References are sorted chronologically as they appear in the manuscript

not alphabetically. That is fine but some references have DOI but some of them do not

have.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

This review spotlight India and highlights the uneven distribution of PhenoCam sites. It collected information of comparison among PhenoCam, satellites, flux, and individual species from published papers. It is meaningful to promote the development of PhenoCam sites. There are several questions that need to be clarified before publishing.

(1) Line 65-68: I believe the Pan European Phenology database (PEP725) is also an important ground-based dataset.

(2) Line 78-80: “Global phenological studies …”. The conclusion is biased. There are still a lot of inconsistent results from satellite data. Sufficient summary is required.

(3) Figure 3a: Which phenophase does the r values indicate? For example, the “DF low”, do the r values indicate SOS, or EOS, or all phenophases the authors collected? How many samples do the authors collect?

(4) Line 132-133: “we compared PhenoCam …”. Did the authors compared the key phenological transition dates derived from GCC and MODIS/VIIRS NDVI, or directly compared the GCC time series and NDVI time series? Please clarify this, as well as line 143-144.

(5) Line 168-173: “Moreover, in the context of …”. A lot of studies have used PhenoCam data to validate remote sensing derived LSP. The simple summary here is insufficient.

(6) Line 272-278: The authors listed two examples in India. Are there any more digital cameras being installed? How many digital cameras are installed in India by now? The authors should provide more sufficient information.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

This study presents a review of Global PhenoCam monitoring. It is an interesting topic, however, the author failed to set up the context of this review. Limitations of other instruments of phenological monitoring are not the main part of this review. The basis of the review should be solid on the importance and significance of the PhenCams and how this review is helping for a better monitoring system. In fact, the integration of Satellite Remote Sensing is a key to up-scale site-specific observations from the  PhenoCams to local or regional scales. How the literature and the data were searched for the study. Authors should add methods. In fact, it more looks like a short communication. 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 4 Report

This review showed an urge to establish PhenoCam network across India for monitoring vegetation dynamics and improving forest management. The evidence came from the imbalanced global PhenoCam distribution and long-term gaps in the long-term records of forest phenological calendars. I would say it is important to set up such an advanced camera in India, but at the same time, this review didn’t comprehensively analyze why PhenoCam records were so important in phenology communities and how we can see through PhenoCam imageries. Here are some of my major concerns:

1.     Section 2 - Methods for monitoring Phenology

First, I believe the authors missed a big portion of ground observations from UN, PEP725 dataset. [for more info： An optimal method for validating satellite-derived land surface phenology using in-situ observations from national phenology networks] The most important information in this section should be what we can see from PhenoCam, ground-observations, and satellite imageries. The footprint mismatches, scale issues, and temporal differences should be highlighted with detailed information.

2.     Section 3 - PhenoCam as a promising technology for long-term and continuous phenological 99 monitoring

In this section, the reason why different vegetation indices, and color indices (GCC, RCC, etc.) show shifts in phenological behaviors of various vegetation types should be investigated rather than just list the previous studies and the comparison results. Some examples like “GCC is more related to pigment contents, NDVI et show higher correlations with FPAR, PAR et.” Investigation of underlying mechanisms among the phenological shifts of different phenological detections (especially the PhenoCam GCC/RCC here) is much more important than just showing what you found in the literature.

Some other comments:

1)    Line 12. Please show the full name of the UAV for broader readers to understand.

2)    Figure3. why didn’t show croplands and shrub lands in panel-c?

3) Figure3. MODIS and VIIRS phenology/NDVI have differences inside? how to make them consistent? and you only show the MODIS in Fig. 3?

4)    Line 171: you may need to dig out the potential reasons why the GCC and Satellite VI show systematic differences in phenological detections. GCC is more related to the pigment contents, while VI is more related to FPAR, structural information, and so on.

5)    Figure 4: IPCC AR6? Why use the regions to map the PhenoCam distribution? Why don't just use the country border to do so?

6)    Line 337: “This will help in validating satellite-derived phenological matrices  (e.g. MCD12Q2)” Please consider more about why there are no many works using PhenoCam observations to validate 500 m – scale satellite phenology records. Some explanations should be stated in this section.  

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Line 86-88 “phenological studies at Global scale have confirmed a 86 significant advancement in the SOS by 0.38 days per year, a delay in the EOS by 0.45 days 87 per year, and a global increase in the LOS by 0.8 days per year [24].”

How could you use the results from only one phenological study to represent “phenological studies”? Please change “phenological studies” to “a phenological study”.

Author Response

Line 86-88 “phenological studies at Global scale have confirmed a  significant advancement in the SOS by 0.38 days per year, a delay in the EOS by 0.45 days per year, and a global increase in the LOS by 0.8 days per year [24].”

How could you use the results from only one phenological study to represent “phenological studies”? Please change “phenological studies” to “a phenological study

Thank you for pointing it out, we have modified the text as follow.

Using satellite data, Julien et al shows that, globally a significant advancement in the SOS by 0.38 days per year, a delay in the EOS by 0.45 days per year, and a global increase in the LOS by 0.8 days per year.

Reviewer 3 Report

I am happy with the revised version. 

Author Response

Thank you for your helpful review comments, they've greatly strengthened the manuscript. 

Reviewer 4 Report

1. The second question I mentioned has not been addressed at all! And the answer is not related to what I asked. please at least let me know very clearly the reason why you think my question is not necessary to be answered. 

2. At the same time, please go through your review paper, lots of materials lack sound citations (ref.). Ex. line 64-67. All these networks should be properly cited with the correct citation or show the website. 

3. about the question: "Figure3. why didn’t show croplands and shrub lands in panel-c?" how could the number of cropland-related articles be limited? This is a review paper, the comprehensiveness is really important to broader readers. And if the authors do not want to add the cropland-PhenoCam-related works, please show reasonable reasons. 

Author Response

Please see the attachment

Author Response File: Author Response.docx