Forest Height Inversion by Combining Single-Baseline TanDEM-X InSAR Data with External DTM Data

Round 1

Reviewer 1 Report

This manuscript focuses on forest height inversion by combining single-baseline TanDEM-X InSAR data with external DTM data. There are many defects in it.
1.In line 3 of page 2 and line 3 of Sec. 2.1, "[12], [13]" should be replaced by "[12, 13]".
2.In line 18 of page 2, "[18], [10]" should be replaced by "[18, 19]".
3.In Eq. (2), "k_z" should be replaced by "k_z'".
4.In Eq. (2), what is "theta"?
5."h_nu" is the final parameter for the proposed method. In Eq. (2), how to derive "gamma_nu" with the unknown "h_nu"?
6.In Eq. (5), what is "P"?
7.In Eq. (6), is the value range of "phi^0_InSAR" [0,2pi] or [-pi/2,pi/2]?
8.In Eq. (9), what is "P"? can "P" be calculated with the unknown "h_nu"?
9.In Fig. 1, "h_nu" must be shown.
10.In the line above Eq. (11), "[12][13][24],[25]" should be replaced by "[12, 13, 24, 25]".
11."h_nu" is the forest height in Eq. (2), but "h_nu" is the canopy height in Eq. (13). What is correct?
12.In the line above Eq. (14), "[14][26]" should be replaced by "[14, 26]".
13.In Eq. (14), why is "zeta" =0.8 used?
14.Is "h_nu" calculated by using Eq. (12) or Eqs. (13) and (15)?
15.In Eq. (16), what is the parameter "phi^0_InSAR"?
16.In Eq. (16), the operation is not an equation.
17.In the second line below Eq. (16), "[6], [21], [22]" should be replaced by "[6, 21, 22]".
18.In the caption of Fig. 5, "Tandem-X" should be replaced by "TanDEM-X".
19.What are the really used value of "lambda" in Eq. (3)?
20.Complex numbers (e.g. "gamma") and real numbers (e.g. "mu") should use different symbol styles which can be identified easily.
In conclusion, major revision is necessary.

Author Response

Author Response File: Author Response.docx

Reviewer 2 Report

The paper presents a methodology to estimate forest height using InSAR-based DEM and external DTM data. The proposed random-volume-over-ground method is compared to the other three approaches and the results are supported with statistical outputs.  Although the study has limitations, it offers outputs that may interest the reader. The following questions regarding error information are expected to be answered.

1.     Please provide the RMSE values with percentages. As mentioned, the three heights are mostly concentrated between the 3 and 9 range. Thus, 3 m RMSE will be a 30% error when it is 9 m.

2.     In section 5.2 it is mentioned that when the slope is below 5°, the lowest RMSE is 1.34 m. What is the range of three heights in each slope? The percentage of RMSE values should also be included.

3.     Considering the error range, what is the difference in similar estimation studies? The results can be briefly compared to the literature.

4.     Figure 15: the letters a to d are missing.

Author Response

Author Response File: Author Response.docx

Reviewer 3 Report

This article mainly focuses on the estimation of canopy height by combining TanDEM-X InSAR with DTM and the explicitation of the RVoG inverion process by relating PD to PCH. It is a meaningful work. The modification suggestions are as follows:

1. The citations of the used formulae are in a mess. But it could not find the sources of several ones.

2. The eta of Formula.14 is a constant 0.8 in the existing researchers. Why does it change to a weighting factor? Why is the exponent 0.8 not parameterized?

3. Are the similar factors of formulae in different researches able to directly be replaced or approximated? 

4. The introduction of the test sites is too ambiguous.

5. Please provide the comparison experiment to prove the robustness of the proposed method.

6. The error analysis is insufficient.

Quality of English language is good with minor editing.

Author Response

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

This revised manuscript is ready to be published.