Dear Authors,

The manuscript addresses an important new method of measurements of water surface elevations using SWOT, with a virtual-reality numerical experiment on two reaches of the Amazon River. However, the main issues raised by both referees is that the authors should make a further effort to highlight the originality of the work and discuss the cases where the method could be applied:

i) discuss the domains and limit of application of the new method in comparison to classical ones;

ii) clarify all the steps involved in matching the hydraulic model and the remotely sensed data;

iii) justify and discuss the strong assumptions of additivity of a noise related to SWOT measurements and a perfect knowledge of channel friction and bed erosion;

iv) how to deal with the complexity of the flood plain, eventual changes or uncertainties of topography, influence of the vegetation, etc. ?

v) discuss the representativeness of the two studied reaches on the Amazon River;

vi) give a list of rivers where SWOT could be successfully applied, and what wide the possible audience of this paper might be ?

vii) discuss how conclusions from the two study cases can be extended to other cases.

The paper will be reconsidered after revisions of the points raised by both referees are being taken and included into the manuscript. Please highlight clearly what you changed in the revised manuscript, so the reviewers are able to assess your changes.

Kind regards,

Roger Moussa

Dear authors,

Thank you for the revised version of the manuscript which addressed all the comments of reviewer # 2 and some of the comments of reviewer #1. As stated by both reviewers, the paper is now clearer and was improved by taking into account a part of reviewers’ comments. I agree with both reviewers that the topic of the paper is of international interest and worth publishing, and I agree with the recommendations of reviewer #1 asking for more details in order to better understand the method and the conclusions.

I think this paper cannot be published in its present form. The paper will be reconsidered after revisions of the points raised by reviewer #1 (see below). Please highlight clearly what you changed in the revised manuscript, so the reviewer will be able to assess your changes.

Kind regards,

Roger Moussa

Dear Authors,

I can now inform you that the reviewers and editor have evaluated the manuscript " Swath altimetry measurements of the mainstem Amazon River: measurement errors and hydraulic implications " (M.D. Wilson, M. Durand, H.C. Jung, and D. Alsdorf). As you will see from the comments below, minor revision has been requested.

Please consider the reviews to see if revision would be feasible. Should you disagree with any part of the reviews, please explain why. I hope that you will find the comments to be of use to you and am looking forward with interest to receiving your revision.

Thank you for submitting your work to Hydrology and Earth System Sciences.

With kind regards,

Roger MOUSSA


Suggestions for revision (from Referee #2):

Most of my questions or remarks received suitable answers in this new version of the paper. But I still disagree on two parts that are in fact additions to the original paper and that I think are mainly opinions of the authors and are not parts of their research work. My opinion is that both parts aim at underestimating the potentialities of field measurements and overestimating the potentialities of satellite observations. The authors demonstrate the potential use of their method on wide rivers on which discharge remains rather steady during long periods of time. On narrow rivers with discharges varying rapidly, continuous field monitoring is much better and there are new field techniques (for instance, measurement of surface velocity) to obtain accurate discharges.

Thus, I still recommend canceling (or replacing by one simpler sentence) the paragraph of the introduction dealing with rating curves (lines 70-98). Other field methods are not quoted and/or the references are certainly not the more relevant ones. Apart wide rivers with mainly single channel, the cases in which field measurements are difficult are also the cases in which satellite observations will not bring enough information.

Figure 15 (and the text around) is misleading because it shows only one cause of error. One will reproduce this figure without caution and will write that satellite can provide very accurate results which are not the case except for very specific cases. Particularly, the results cannot be extrapolated to narrow rivers (say width below 500 meters) and thus should be excluded on figure 15. Thus, because this figure 15 can be discussed a lot, I propose to cancel it and to modify the text around (lines 685-754) accordingly.

Dear Authors,

All reviewers’ comments were addressed in a satisfactory manner. I can now inform you that the manuscript " Swath altimetry measurements of the mainstem Amazon River: measurement errors and hydraulic implications " (M.D. Wilson, M. Durand, H.C. Jung, and D. Alsdorf) is accepted for publication.

Thank you for submitting your work to Hydrology and Earth System Sciences.

Kind regards,

Roger MOUSSA