Rice Crop Height Inversion from TanDEM-X PolInSAR Data Using the RVoG Model Combined with the Logistic Growth Equation

Round 1

Reviewer 1 Report

 Crop height is one of the critical vegetation biophysical parameters, which is useful to many applications, such as phenology tracking, crop health evaluation, total yield prediction. The monitoring and forecast of the crop height is necessary and meaningful. This manuscript aimed to invert crop height from PolInSAR data using the RVoG Model Combined with the Logistic Growth Equation, which is valuable and interesting. The findings will contribute to the crop height monitoring with remote sensing in the future. However, there are some major flaws which need to be addressed before publication.

(1) There are some challenges for the application of the height monitoring using the PolInSAR data, due to the height of rice is too short compared with forests and trees. It is suggested to add more analysis about the detail parameters of the TanDEM-X dual-polarization data used in this manuscript to indicate the feasibility and research gap of this study.

(2) For the modified RVoG model used in this study, more than three different dates should be selected for enabling inversion.  Is it the sowing date is necessary? Only selected three dates (i.e., three pairs of extreme coherences) as the observation input. How to determine the input dates of the model for the other rice fields except the three paddy fields labelled as Minima, Calonge and EIReboso? It is suggested to add more analysis and discussion.

(3) It is suggested to add some analysis and discussion of the potential application of the model and method proposed in this study, such as the monitoring of rice height in other regions, and other crops.

(4) Figure 7. The relative errors of the vegetation height of at the three test plots are different obviously. It is suggested to add some analysis of the reason.

(5) Figure10. It is suggested to add the meaning of the vertical axis. 

(6) The quantitative comparison presented in Figure 11 and Figure 12 indicates that the inversion with the proposed date selection can adaptively select the inputs at pixel level and achieves a relatively good accuracy. However, it is not the best. It is suggested to add more data or analysis to indicate the advantages of the model proposed in this manuscript.

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The study estimated rice heights based on PolInSAR imagery and a modified RVoG model considering and assuming a logistic plant height growth with time. The manuscript was concisely written and provided a straightforward examination of the proposed methodology. Below are my specific comments.

Most sentences in the abstract should be in past tense.

Data was vaguely described in the material section. The authors should add more details to this section wherever necessary aside from my suggestions below.

How many ground truth measurements per field and in total? One height per field per date?

How exactly were the ground truth heights measured?

What is the vertical and horizontal resolution of the PolInSAR data?

Line 108-111, 120-121 provide data source links.

Section 3 is highly abstract. Why not add a graphical illustration of PolInSAR image processing similar to Figure 4 for more clarity to readers?

The manuscript is poorly structured. Figure 3, Table 2, and their associated texts belong to the result section. The entire “5. Discussion” section also belongs to the result section. The content of the manuscript needs to be substantially rearranged. I suggest just having a “result and discussion” section.

Both days after sowing and DoY are used in different figures. Consider using only one of them for consistency and clarity.

I am in doubt of the accuracy and reliability of ground truth. For example in Figure 5, some height values at certain dates are smaller than the adjacent values measured both before and after them and are apparently erroneous. A quantitative evaluation of the ground truth accuracy should be carried out, and a justification of the ground truth inaccuracy for the study needs to be provided.

I disagree with the usage of the phrase “interferometric sensitivity”. The authors argued that the large initial height estimation errors were due to insufficient interferometric sensitivity, which might be or might not be true. Is there a possibility that the interferogram data were sensitive enough to react to short height changes, however, the data accuracy itself was too low or the data processing methodology was not sophisticated enough to fully exploit the data? Just because your final estimated heights weren’t accurate doesn’t necessarily mean your raw data was “insensitive”.

This manuscript has a major and fundamental flaw. The innovation of the study was the incorporation of plant logistic growth equation into the RVoG model. However, to demonstrate the superiority of the proposed methodology, the comparison between rice heights estimated using RVoG models with and without plant logistic growth equation must be presented, which is missing in the manuscript currently.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The manuscript has been well revised according to the comments.

Reviewer 2 Report

The authors have properly addressed all my comments. I recommend its current form for publication.