Retrieving Soil Physical Properties by Assimilating SMAP Brightness Temperature Observations into the Community Land Model

Round 1

Reviewer 1 Report

Overall, authors attempted to make a little complicated experimental design using several models, and locally collected many datasets from the field. However, I would like to cast a fundemental question for their long-term study aim which is written on the bottom of this comment.

In addition, there are several awkward expressions. For example, you assimilate observations into a model. So, the first sentence of abstract is supposed to be :

"This paper assimilated a uniform passive and active observation, namely an enhanced physically-based discrete emission-scattering model, into the community land model (CLM) through local ensemble transform Kalman filter (LETKF) system"

Similarly, title could be :

Retrieving Soil Physical Properties by Assimilating SMAP
Brightness Temperature Observations into the Community Land
Model 

Abstract: please report your results, quantitatively. After assimilating the Radar backscatter products to further constrain soil and vegetation parameters, how much improvement could you achieve, quantitatively in terms of your own error metrics. However, it seems that in this study authors did not assimilate radar backscatter products. It is for future studies, So it should be deleted and please focus on what you have illustrated by this study. Please rewrite abstract to clarify your findings better.

Abstract says that improvement was limited due to imperfection of CLM model. However, data assimilation assumes a perfect model, So, as long as we provide accurate input, assimilation analysis result should produce improved outcomes.

Introduction

please suggest novelty of your study. I think this experimental design is similar to previous studies. You might want to say that you have improved SM and land flux as compared to reference data through Figure 7 and 8.

Materials and Methods

For AIEM, You used local observations for the surface roughness parameters (i.e., the standard deviation of surface  heights  ?? of 0.9 cm, correlation length of surface height ?? of 9 cm, and the exponential  autocorrelation function). Do you think this can acheive spatial representativenss. I can't see figure or description for how much big your spatial domain is from this section.

Similarly, there is no resolution information for  SMAP Level-1C and radar data, which has several different resolutions from 1km to several kilometers. If you used low resolution, that affects the interpretation of results. 

There is no description for satellite bias correction. The main difference between field measurement data assimilation and satellite data assimilation is that bias correction. Although it is arguable whether bias correction works or not, you still need to provide how you processed SMAP TB and radar backscatter bias in your experiment design, and whether there were rain events that may possibly disturb the signals.   

Results

I can't see Open Loop from Fig 9.

Please indicate whether 'obs' in Fig 7-9 implies local in-situ point data or SMAP soil moisture or eddy covariance heat flux data. That makes a huge difference in interpretation.

Overall, It is doubtful whether the objective of satellite data assimilation is to go towards, and to be the same with the local observations. Satellite foot-print is huge (I don't know which resolution authors used as they didn't say that). If using this method and approach, then it will be difficult to up-scale to heterogenous large scale sites in the future. The more Authors rely on the local information, the more difficult it is to go to large scale.

Author Response

Dear Reviewer,

We sincerely thank you for your quality review of our manuscript. Please see the attachment for our responses to your comments. 

Sincerely

 

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript attempted to retrieve Soil Physical Properties by Assimilating SMAP Brightness Temperature Observations in the Community Land Model. The objective is well founded, however my major concern is the representation of the results and discussion are not up to international standard. So I am afraid of the acceptance of this paper in the present form.

comments:
My major concern is the way of representation. e.g.
readers outside of this topic don't know the terms TBP, TBH, TBV and SM in the abstract. Please provide the necessary information for what they stand for.

L52:53: "To obtain basic soil properties and associated SHPs at the large scale (e.g., km scale of LSMs), the data assimilation (DA) strategy combining LSMs and observations has been investigated.": Where is it investigated?

L57-58: "SM DA": It is confusing. Write their full names.

L112-117: " (2) In the first place, investigate whether the passive Soil Moisture Active and Passive (SMAP) ???? ?? assimilation improves estimates of basic soil properties and their vertical descriptions. If so, does the refined soil property characterization improve estimates of SM and soil temperature profiles and then land surface heat fluxes with the CLM? (3) Investigate whether the retrieved soil property is polarization dependent ": Are you describing your objectives or asking the reader to do it for you?
Please write in the proper way.

2) The texts in all the sections need to be brushed up. Also some paragraphs lack suitable headings/subheadings.

3) I did not find in detail what kind of hypothesis was taken in this study. Please discuss it somewhere in the manuscript.

4) There are plenty of works already conducted on this issue in many regions across the world. You have also highlighted many in the introduction. But none of such works have been discussed in the results section. Thus, it is strongly suggested to provide a discussion of your results with comparison to other methods and studies.

Author Response

Dear Reviewer,

We sincerely thank you for your review of our manuscript. Please see the attachment for our responses to your comments. 

Sincerely

 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

I appreciate the authors' effort. I confirm some of my comments are addressed, but my major comments are avoided. I DIDN'T SEE ANY MAJOR REVISION made in this manuscript. Perhaps authors have assumed that their presented materials are sufficient and no further modifications/improvements are required. If this is the case, then reviewers shouldn't waste their time on reading this manuscript.

Comment 1 - I agree that English native editors improve the language, but it is the authors responsibility to check the content and science. e.g.

L262-263: "Uncertainties that affect the model prediction performance are assumed to be due to errors in the basic soil properties and atmospheric forcing data." Why does this uncertainty and error appear here? 

L 274-276: "the basic soil texture does not change dramatically due to the aforementioned complications, although the soil hydraulic properties can be altered due to the presence of ice". This is confusing. What is your consideration here?

L300-305:"Utilizing the measurements of soil property profiles [23] and an exponential formulation adopted by the CLM (to obtain fine soil layers near the soil surface), the obtained depth ratios regarding the organic matter content and sand fraction at the Maqu site are [1.0, 0.98, 0.95, 0.45, 0.28, 0.18, 0.12, 0.07, 0, 0] and [1.0, 1.02, 1.06, 1.12, 1.14, 1.16, 1.18, 1.19, 1.21, 1.23], respectively, for the ten soil layers (see Table 1)." It is a long sentence and so confusing. What is that exponential formulation?

Comment 2 - Do you mean "whether SMAP TBP assimilation improves estimates of soil properties?" is your hypothesis. Then how is this different to your objectives? 

Comment 3 - Authors replied that "As you already see in the Introduction, the main contribution of this paper is including a physically-based uniform passive and active microwave observation operator in a land DA system for the first time." Then what have you done here? What kind of improvements in the soil parameters you found COMPARED to other studies?

Author Response

Dear Reviewer,

We sincerely thank you for your time and effort in reviewing our manuscript. 

Please see the attachment for our responses to your comments.

Author Response File: Author Response.pdf