Evaluation of Spaceborne GNSS-R Retrieved Ocean Surface Wind Speed with Multiple Datasets
Round 1
Reviewer 1 Report
See attached document.
Comments for author File: 
Comments.pdf
Author Response
Please see the attachment.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The paper illustrates some latest investigations for building up geophysical model functions related to GNSS-R wind speed retrievals. Even if the method has been thoroughly investigated in the past, authors provide some improvement in the retrival method and a well-conceived validation based on multiple datasets.
At the same time, this reviewer finds that the description of the method as well as the level of refinement of the work must be improved before journal publication. The recommendation is to follow the suggestions (provided hereafter and with more details in the attached document) and to resubmit the paper.
Major recommendations
Differences pros and cons with respet to previous methods has not been clearly analyzed. This could be considered in the introduction after removing well known and standard material (see attached file).
The description of the wind retrieval algorithm is not well written. Understanding is difficult even for experts in the field.
Clarity of writing and language must be improved, in general.
Minor recommendations
Suggestions are provided in the attached manuscript. It is also suggested to mention and discuss the following references
[1] H. Park, E. Valencia, N. Rodriguez-Alvarez, X. Bosch-Lluis, I. Ramos-Perez, and A. Camps, “New approach to sea surface wind retrieval from GNSS-R measurements,” in Proc. IEEE Int. Geosci. Remote Sens. Symp., Jul. 2011, pp. 1469–1472.
[2] F. Huang et al., "Sequential Processing of GNSS-R Delay-Doppler Maps to Estimate the Ocean Surface Wind Field," in IEEE Transactions on Geoscience and Remote Sensing.
[3] Y. Liu, I. Collett and Y. J. Morton, "Application of Neural Network to GNSS-R Wind Speed Retrieval," in IEEE Transactions on Geoscience and Remote Sensing, 2019.
[4] G. Giangregorio, P. Addabbo, C. Galdi and M. d. Bisceglie, "Ocean Wind Speed Estimation From the GNSS Scattered Power Function Volume," in IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, vol. 12, no. 1, pp. 78-86, Jan. 2019.
Reference [23] should be removed because out of paper context.
Comments for author File: Comments.pdf
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Reviewer 3 Report
With great pleasure I've read this interesting and well written contribution.
Even if I'm not a strong expert in this research field, the paper is understandable and interesting. It is rarely to find a paper well written like this one. So, I suggest to accept the paper as is, after a brief check of the English language (I've found a typo).
Author Response
Thank you very much for your review.
Reviewer 4 Report
Manuscript ID: remotesensing-615067
Title: Evaluation of spaceborne GNSS-R retrieved ocean surface wind speed with multiple datasets
Zhounan Dong , Shuanggen Jin
The paper evaluates a refined spaceborne GNSS-R ocean surface wind speed retrieval algorithm. Ocean surface wind speeds are evaluated using the ground surface true wind speed (10 m surface winds) from Numerical Weather Prediction products: using ERA 5 from ECMWF (wind field product at 0.25degx0.25deg) and NCEP GDAS products providing global surface flux grid products. The GNSS-R wind speed retrievals are also validated with buoy observations from the National Data Buoy Center (NDBC).
The article is innovative in making use of a variety of data sets to evaluate the spaceborne GNSS-R retrieved ocean wind speed from CYGNSS using the wind speed retrievals from ERA5 and GDAS, wind speed retrieval based on CCMP - this platform combining measurements satellite microwave winds and instrument observations.
However I would suggest to better define the objectives of the study with regard to existing literature.
Major comments
Pease detail better the challenges and add some additional references to underline better why a faithful ground reference wind is needed for spaceborne GNSS-R wind speed retrieval.
Section 2.2 DDM observables
Please detail the acronyms : DDMV, ADDMV, TES
Discussion section:
I would rather start with the purpose of the paper and not start with the things the paper does not discuss.
Conclusions:
Lines 431-432: you mentioned that “new constraints are added in the processing of smoothing discrete empirical GMF to eliminate fake fluctuation.. ” Could you add more details about this procedure ? What are the benefits expected - trying to quantify these improvements.
Minor comments
Figure1: tipo errors please replace ios-Delay and ios-Doppler by iso
Section 2.2 line 155:
I would replace leading edge slope with Leading Edge Slope to make it clearer.
Section3: Results and validation
Line 237: two datasets are mentioned: which one do you use ?
Section 3.1: lines 255 to 258
Could you explain the reason of this choice and add more details accordingly ?
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Round 2
Reviewer 4 Report
Thank you for the comments and modifications brought to the manuscript.
The article is of high quality, innovative and is suitable for publication in the present form.
