Wave spectral shapes in the coastal waters based on measured data off Karwar on the western coast of India

Nair, M. Anjali; Kumar, V. Sanil

doi:https://doi.org/10.5194/os-13-365-2017

Articles | Volume 13, issue 3

https://doi.org/10.5194/os-13-365-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/os-13-365-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 13, issue 3

Technical note

|

03 May 2017

Technical note |

| 03 May 2017

Wave spectral shapes in the coastal waters based on measured data off Karwar on the western coast of India

M. Anjali Nair and V. Sanil Kumar

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Final revised paper (published on 03 May 2017)
Preprint (discussion started on 06 Jan 2017)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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- Supplement

RC1: 'Review', Anonymous Referee #1, 05 Feb 2017
- AC1: 'Response to the comments of Reviewer 1', Sanil Kumar, 28 Mar 2017
RC2: 'Wave spectral shapes in the coastal waters based on measured data off Karwar, west coast of India', Anonymous Referee #2, 08 Mar 2017
- AC2: 'Response to the comments of Reviewer 2', Sanil Kumar, 28 Mar 2017

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Sanil Kumar on behalf of the Authors (28 Mar 2017) Manuscript

ED: Referee Nomination & Report Request started (29 Mar 2017) by Andreas Sterl

RR by Anonymous Referee #1 (06 Apr 2017)

Suggestions for revision or reasons for rejection

Line 74
"This study shows that the percentage of swells in the measured waves was 75 to 79% at the locations with higher percentage of swells in the northern portion of AS compared to that at the southern side."

-- Unclear, please restate.

Line 112
-- Chart datum is ambiguous. A chart datum is likely a mean-low-lower-water or some other tidal datum. A tidal datum is not a geodetic datum. In this era of sea level-rise consciousness, it would be nice to have the geodetic water levels quantified, but you seem unwilling to invest the effort. I don't see the advantage of belabouring this point since it's the relative change in sea level that is apparently the point of this text. Why not just avoid the technicality of understanding what a geodetic datum is, which one applies, the needed transformations from a chart or tidal datum, and just say that there is a 24 cm annual cycle in mean sea level from September to January.

Line 159
"An exponential curve y = k.f^b is fitted for high-frequency part of the spectrum"

-- what is k.f? Apparently k is a coefficient?

Line 236
"Since the range of maximum spectral energy density in a year is large (~ 60 m^2 /Hz), each wave spectrum is normalised through dividing the spectral energy density by the maximum spectral energy density of that spectrum."

-- So you are 'normalizing' each spectra independently. Why would one do this? This complicates the utility of the spectral amplitude since each spectra has it's own unique scaling and cannot be directly compared to another spectra, nor can actual water level amplitudes be recovered from the spectra without the specific scaling.

When you say that "each wave spectrum is normalised through dividing the spectral energy density by the maximum spectral energy density of that spectrum", are you literally normalizing each individual spectrum, or are you normalizing the entire spectrogram over each year? The former is unacceptable, the latter imposes that year-to-year amplitude comparisons must be scaled.

To the point of spectral amplitudes, you note that wave spectra have physical units (m^2/Hz), thereby one can obtain an RMS wave height at any frequency if the spectral amplitude is known. Clearly that has been obviated by your normalization and the amplitude scale in figure 5 of [0,1].

The reader is not in a position to know how the spectral normalization is applied in time and to what extent individual spectra can be compared to each other, or that a physical measurement can be extracted from the data presented in figure 5. One of the strengths of this paper is its data coverage and analysis. To remove the ability for the reader to extract a physical amplitude from the data, or to have a uniform comparison across time is difficult to understand.

These same comments/issues apply to figure 9 and the monthly mean spectral amplitudes.

If one desires to address that "the range of maximum spectral energy density in a year is large", a conventional approach is express the spectral power in decibels.

Line 379
"The values for α and γ were randomly varied within a range to find out the values for which, the theoretical spectrum best fits the measured spectrum and those values were used to plot the theoretical spectrum."

-- This issue remains unanswered. You have not specified what "randomly varied" and "over a range" mean. If your work is to be reproducible, should not you reveal the methods?

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RR by Anonymous Referee #2 (07 Apr 2017)

ED: Publish subject to minor revisions (Editor review) (10 Apr 2017) by Andreas Sterl

AR by Sanil Kumar on behalf of the Authors (10 Apr 2017) Author's response Manuscript

ED: Publish as is (12 Apr 2017) by Andreas Sterl

AR by Sanil Kumar on behalf of the Authors (12 Apr 2017)

Short summary

The information on wave spectral shapes that is required for designing marine structures is presented based on wave data collected from January 2011 to December 2015 in the coastal waters of the eastern Arabian Sea. The variations in the high-frequency tail of the wave spectrum in different months are presented. The slope of the high-frequency tail of the monthly average wave spectra is high during the Indian summer monsoon period (June–September) compared to other months.