Assessing the Future ODYSEA Satellite Mission for the Estimation of Ocean Surface Currents, Wind Stress, Energy Fluxes, and the Mechanical Coupling Between the Ocean and the Atmosphere

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors The study of ocean surface currents and air-sea interaction are currently at the forefront of ocean remote sensing. The authors generated synthetic ODYSEA data using a simulator, ODYSIM, to evaluate the estimation performance of surface currents and wind stress for the future ODYSEA mission. The results shows that the ODYSEA would significantly improve the monitoring of eddy kinetic energy, kinetic energy cascade, and air-sea kinetic energy flux in the Gulf Stream region. The paper is very well written, and has a reasonable organizational structure. I have few comments and questions below: 1. Line 96: What is the carrier frequency of the transmit signal in the ODYSIM? Will the carrier frequency affect the measurement performance of sea surface currents and wind fields as described in lines 104-105? 2. Line 229, Figure 3: How is the relationship between wind speed and the mean noise of the surface currents obtained?

Author Response

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Reviewer 2 Report

Comments and Suggestions for Authors

Assessing the Future ODYSEA Satellite Mission for the Estimation of Ocean Surface Currents, Wind Stress, Energy Fluxes, and the Mechanical Coupling between the Ocean and the Atmosphere

 

Manuscript 3333274 submitted to Remote Sensing

 

General overview

The manuscript presents an objective analysis of the future ODYSEA satellite mission through the use of the scatterometer simulator called ODYSIM applied to numerical simulations generated by a high-resolution regional coupled atmosphere-ocean-wave model called Coastal and Regional Ocean Community (CROCO).

With this procedure, virtual sets of observations with/without temporal and/or spatial filtering and/or noise are extensively tested to assess how well ODYSEA could measure surface winds, currents, energy fluxes, and ocean-atmosphere coupling coefficients. The focused region is the Gulf Stream which is characterized by strong and large mesoscale and submesoscale currents, as well as large surface gravity waves.

The structure follows the standard, the length is adequate, the language needs no improvement, figures and tables are indispensable.

I have only minor comments to improve the manuscript. My opinion is accepted with minor revisions.

 

Specific comments

Line 33-36: “The sink of kinetic energy caused by CFB arises from the interaction between surface currents, winds, and wind stress: a positive (negative) current anomaly induces a negative (positive) wind stress anomaly and, hence, a positive (negative) wind anomaly [5].” This phrase is quite strange and counterintuitive in the last part; besides, the mentioned reference deals with wind vorticity, and not the wind stress itself. My suggestion is to rewrite it to avoid misinterpretation.

Lines 510-512 & lines 547-551: the content of these phrases should be included in the abstract.

Lines 620-623 & lines 632-634: the content of these phrases should be included in the abstract.

Page 27, caption of Figure 5: “QUIKSCAT” should be “AVISO”

Author Response

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Reviewer 3 Report

Comments and Suggestions for Authors

1. In the system simulation process, this paper focuses on the introduction of the numerical coupling used as an input source. However, there is no mention how to simulate Doppler radar signals and how to extract information from radar signals. Please adding content in this area.

2. Please give the formula of ocean surface kinetic energy, wind stress, kinetic energy, air-sea energy fluxes, and ocean-atmosphere coupling coefficients etc. And please give some ground truth for validation.

Author Response

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Reviewer 4 Report

Comments and Suggestions for Authors

The manuscript by Larrañaga et al. presents a useful enhanced assessment of the sampling capabilities that will be provided by the proposed ODYSEA satellite mission.  The work presents a clear, structured analysis of the potential capabilities with respect to several of the key desired parameters.  I believe this work can be a valuable addition to the literature, however, I feel it first needs to more explicitly address any potential differences between the actual final observations/retrievals from the satellite and the simulated characteristics presented here.  My recommendation is for publication following revision to address this concern for an audience not intimately familiar with this mission.

 

As a reader familiar with satellite sampling (and the associated limitations) of similar parameters but less so with the specific instrumental developments related to this mission, at the end of this manuscript I was left with a lingering question as to how well the final results derived from actual future satellite observations will compare in accuracy with the simulated results here.  The manuscript accurately speaks in terms of “sampling capabilities” in many places, but the connection that exists to final measurement capabilities made solely through the instrumental noise could benefit from more detailed explanation. 

 

The manuscript speaks of the simulator’s ability to include random errors or noise (line 102) and the overall previously estimated wind and current errors (lines 69-71, 103-105), but I am struggling with making the connection between the noise discussed in the paper and these errors.  The initial mention of the noise in lines 209-213 seems to lack detail that I need to understand the connection.  If this is captured in the references, I think something more is required here for this paper to be a bit more self-sufficient.  Fig. 3 first presents “full” and “half” noise, but there is no mention in the text of half noise until section 3.6.  I feel more mention/discussion of this is needed up front in Section 2

 

Moreover, I think more could be said about what went into the “commonly referenced” errors for ODYSEA and the implications for the conclusions here.  Typically, with a satellite retrieval, there are multiple contributions to the overall retrieved product error including sensor noise characteristics and those associated with the physical retrieval.  What all is included here?  Are there specific conditions (e.g., presence of precipitation) where the retrieval is degraded?  Are the retrieval errors fully understood?  How does this potentially impact the conclusions?  Similarly, are there any assumed errors in the AVISO-like and QuikSCAT-like products considered beyond the sampling of the physical fields?

 

I don’t feel a huge amount is required here, but I think there needs to be at least some more discussion in this manuscript of what errors are or are not considered, how that fully impacts differences from “sampling capabilities”, and what implications this might have with respect to the specific conclusions for the different parameters.

 

Other comments:

 

A general note:  Within the manuscript figures are sometimes referenced as “Figure X” and other times as “Fig. X”.  I think consistency should be desirable.

 

Lines 55-57:  In speaking of satellite “products” here, I think the discussion could benefit from more specific mention of explicitly what parameters are being referred to – e.g. wind stress, sea surface height, derived currents? directly retrieved or otherwise derived?  Yes, references are provided, but when speaking of biases, errors, and uncertainties it would be useful to have a more explicit point of reference internal to this manuscript.  Isn’t AVISO an acronym that ideally should be defined outside of a reference?

 

Lines 94-5:  Since ODYSIM seems to be defined just in this manuscript, I think the linkage and relationship to the cited references could be more explicitly described.  To what degree are the simulations the same or different to those in the cited references?  Details are provided on the models used here for the surface conditions, but there is no discussion on the electromagnetic/radiometric aspects.  Are these refined surface aspects but are the radiometric aspects the same?  Are there uncertainties associated with the simulation in addition to or built in to the uncertainties considered in the manuscript?  Some of the missing clarity here could be influencing my more overall concerns.

 

Line 120:  Fig. 2a -> Fig. 1a?

 

Line 138:  I think this continues to refer to Fig. 1 rather than Fig. 2.

 

Line 152:  Sure, ERA5 is well known, but should there be a formal definition outside the reference (CFSR is defined later)?

 

Line 153/186:  For consistency throughout, I think some definition of KIAPS SAS and OASIS would be beneficial.

 

Line 217: swat -> swath

 

Fig 5 caption:  QuikSCAT-like -> AVISO-like?

 

Fig 7 (and 8, 9 other) captions:  The meaning of “0.1 eddy kinetic energy level” is unclear here.  In the Fig. 10 caption a connection to units is drawn – is that the same meaning here and elsewhere?  If so, the definition should be brought forward.

 

Line 371, “construct gridded products”:  A subtlety here, but I understood the L2 products to also be defined on grid points – is the distinction here to provide “spatially complete” products?

 

Line 423:  The use of the word “significantly” here is potentially problematic.  Was there any statistical significance test performed?  Is there a single metric upon which this is based beyond the general shape of the observed dependence?  The assessment here seems somewhat subjective.

 

Line 473:  “os” -> “is” or “of”?

 

Line 568:  Along the lines of my overall comments, is “measurement noise” here solely that?  Is there any potential retrieval uncertainty that would also need to be considered?

 

Line 590: Similar question with respect to “significantly” – the comparisons again are largely qualitative in nature.

Author Response

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The file showing the differences between the paper versions has been uploaded as Non-Published Material.

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