Understanding the Land Surface Phenology and Gross Primary Production of Sugarcane Plantations by Eddy Flux Measurements, MODIS Images, and Data-Driven Models

Round 1

Reviewer 1 Report

The authors have correctly revised the content of the manuscript, taking into account all of the comments.

I recommend the manuscript for publishing in Remote sensing journal.

Author Response

We appreciate your time and effort in reviewing this manuscript.

Reviewer 2 Report

The authors improved the manuscript sufficiently. 

Author Response

Thank you for your time and effort in reviewing this manuscript.

Reviewer 3 Report

Thanks for the answers and revision. I have no more comments except for the unit of radiation.

 

1. " W m^-2 d^-1 " is not a correct unit for short wave radiation or any other radiation flux, because W = J/s, which has the time already there. See the unit table in NCEP webpage https://www.nco.ncep.noaa.gov/pmb/docs/grib2/grib2_doc/grib2_table4-2-0-4.shtml To me, either " W m^-2" or " MJ m^-2 d^-1" is correct, " W m^-2 d^-1 " is wrong, except if you are talking about daily change rate of flux change.
   
2. That 1MJ global radiation (about 300nm~5000nm) = 2.05 moles PAR (400nm to 700nm) makes sense. Since you are using PAR in your manuscript, I thought you were transforming PAR (MJ) to PAR (mole).
   

 

 

Author Response

Thanks again for your time and suggestions.Please see the attachment.

 

Author Response File: Author Response.pdf

Reviewer 4 Report

Overall the authors sufficiently addressed my concerns.

Author Response

Thank you for your time and effort in reviewing this manuscript.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

see attached

Comments for author File: Comments.pdf

Reviewer 2 Report

The manuscript is well written. I enjoy reading it.

 

1. Line 164 Line166 and Line 215 etc: please check the unit of shortwave radiation, should be MJ m^-2 d^-1.
2. S6. Please check if the PAR unit mmol m^-2 day^-1 and that value are correct. They seem too small to me. PAR units and values in Figure 2 seem correct.
3. Figure 9 annual PAR unit and value seem too small and not correct to me again. Please have a check.
4. Line 158, section 4 NCEP Climate data Please describe how you transform downward shortwave radiation (usually 400 to 2500 nm) to PAR (400 to 700nm) used in LUE model.
5. Line 433 to 438. About the unit conversion from gC MJ^-1 to gC mol^-1. Please have a second check.

To me 1 MJ = 4.6 mol

So 1 MJ^-1 = (1/4.6) mol^-1  

And thus 1.63 ~ 2.09 g C MJ^-1 should be  (0.35~0.45 g C mol^-1 PPFD)

Correct me if I am wrong.

If I am correct here, your parameter max LUE of 0.9 g Cmol^-1 (4.14 gC MJ^-1) seems too large. Please provide further evidence to support the max LUE parameter used here.

You may also check David Turner’s work e.g.

Turner, D.P., Urbanski, S., Bremer, D., Wofsy, S.C., Meyers, T., Gower, S.T., & Gregory, M. (2003). Cross biome comparison of daily light use efficiency for gross primary production. Global Change Biology, 9, 383-395Also notice in Reference 77 Robertson et al 1996. Their results about RUE is based on biomass g, not C in GPP. so be aware the numbers are not comparable.

6. Also notice in Reference 77 Robertson et al 1996. Their results about RUE is based on biomass g, not gC in GPP. so be aware that the numbers are not comparable.

 

7. As a ratooning crop, the productivity of sugar cane may decrease with aging. Can the scaler effect of sugar cane age be included in the LUE factor (Equation 7)? The author might need to discuss this point. In current perennial ratooning crop experiments, like perennial rice and wheat, one concern is that the yield (thus LUE) may decrease with aging.

Reviewer 3 Report

The issue of this manuscript is that it has three objectives. Each objective was simply analyzed. As a result, the outcome of this paper is superficial though the manuscript is really long. I strongly recommend that the authors should divide the manuscript into three manuscripts, and analyze each objective more deeply. Otherwise, the scientific meaning of the paper is almost nothing.

Reviewer 4 Report

The results of this study reveal the potential of satellite remote sensing to track LSP events and the development of sugarcane crops. This study also allows to assess the contribution of sugarcane crops to the global carbon cycle.

The main achievements of the presented research are:

• Land surface phenology of sugarcane croplands has been considered in terms of both the seasonal dynamics of eddy covariance GPP and NEE and the seasonal dynamics of vegetation indices (NDVI, EVI, and / or LSWI). Both approaches show LSP from the viewpoint of ecosystem function and from the perspective of ecosystem structure (leaf area index, greenness). Land surface phenology derived by VI and eddy covariance GPP data defines accurately green-up and harvesting dates for sugarcane.
• The VPM is parameterized for sugarcane crops using climate data and MODIS images to estimate daily GPP at the two sugarcane sites. The VPM yields reasonable estimates of GPP in sugarcane during the growing season at the studied
• VPM uses a satellite-derived water index (Land Surface Water Index) to estimate the seasonal dynamics of water stress. The model simulations and reanalysis data show relatively small interannual variations in GPPVPM-NCEP at the Louisiana sugarcane field during the drought years between 2000 and 2018. Therefore, it is desirable future studies to carry out a more detailed analysis of the VPM performance under drought conditions.
• The VPM yields consistent results at a maximum LUE parameter value of 0.9 g Cmol-1 PPFD. This value is reasonable as it is close to the estimates made in other studies on non-irrigated sugarcane.
• It is shown that MODIS Gross and Net Primary Production (GPP/NPP) data product (MOD17A2) underestimated GPP by 66% at the USA site and 59% at the Brazilian site, compared to eddy covariance measurements.

The conclusions are consistent with the evidence and arguments presented and they address the main objectives of the study. The paper is well articulated and the text is clear and easy to follow. There are certain sections where the meaning needs clarifications. To address the unclear sections, the authors should take into account the provided notes and suggestions.

I highly recommend the featured article for publication in Remote Sensing Journal, after the authors address the notes and suggestion made in the text.

Comments for author File: Comments.pdf