The Effect of Attenuation from Fish Shoals on Long-Range, Wide-Area Acoustic Sensing in the Ocean

Round 1

Reviewer 1 Report

Review of remotesensing-610795: ‘The Effect of Attenuation from Fish Shoals on Long-Range, Wide-Area Acoustic Sensing’

This paper uses a unique and remarkable data set to make the case that waveguide effects must be taken into account to correctly interpret long range, wide angle acoustic backscatter.  The paper has significant impact for interpreting and modeling backscatter from fish in applications to determine fish shoal population density.  It also has impact for applications of other inversions of waveguide model parameters: the message is that researchers must ensure that there is no impact on their results from the presence of fish.  The unique data set in which the echo from a distant fish shoal is intercepted by a closer fish shoal enables inference of both the backscatter strength of fish and the attenuation due to fish in the shoal.  Much of the theory used in the paper has been published previously (mostly by one of the authors), and I appreciate the summaries of the work that are presented in the Appendices.  The merit of the paper is the use of the theory in interpreting the data to infer the scattering strength and attenuation.  I recommend that the paper be accepted for publication, with consideration of the comments below.

I have only a few comments that the authors should consider.

The paper deals with fish that have swim bladders. My question is whether the methodology can be applied to shoals of fish that do not have swim bladders. Perhaps the authors could make a comment about this – as an indication of future study? In Figure 3, what is the relevance of the information presented in panels F and G? I could not find any discussion about these in the text or the caption. Lines 191-193. The authors provide only a minimal description of the optimization that was carried out to estimate the five model parameters. I think readers would appreciate more description of the method, because the inversion itself involves correlated model parameters.  For instance, the authors state that the search was done over reasonable values of the model parameters.  Perhaps the authors could provide the model parameter bounds.  Also, I assume that the optimization was carried out as a search process.  Was the search a grid search that involved all the five model parameters simultaneously?  Or some other approach?  I realize that the authors have used a comparison between modeled and measured attenuation and scattering strength, but maybe some of the model parameters do not have realistic values.  Since there is so little information about the inversion, I don’t have enough information to assess the quality of the optimization. lines 257-259. The authors state that their results demonstrate that significant errors can occur without properly accounting for waveguide effects in modeling the sound propagation. Can the authors expand on this statement to point out specifically what you mean?  Perhaps a number to show what magnitude of difference in dB can occur?  It doesn't hurt to repeat what may to the authors seem obvious.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper is interesting and the technical contents as well as results are convincing. The joint model of attenuation and muti-scattering across fish shoals using loglikelihood technique based on waveguide theory, is proposed. The derived theoretical results matches well with the results obtained from the experimental ocean data. The method can be useful to improve the accuracy of the underwater remote sensing for underwater acoustic communication as well as surveillance by reducing the significant effects of attenuation and scattering caused by dense fish groups in the ocean.

 

 

 

 

Author Response

Thank you for your comments.