Effect of orientation on broadband acoustic scattering of Antarctic krill Euphausia superba : implications for inverting zooplankton spectral

Author Posting. © Acoustical Society of America, 1998. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 104 (1998): 2121-2135, doi:10.1121/1.423726.Acoustic scattering experiments involving simultaneous acquisition of broadband echoes and video footage from several Antarctic krill were carried out to determine the effect of animal orientation on echo spectral structure. A novel video analysis technique, applied to extract krill angle of orientation corresponding to each insonification, revealed that echo spectra from krill near broadside incidence relative to the incident acoustic wave exhibited widely spaced, deep nulls, whereas off-broadside echo spectra had a more erratic structure, with several closely spaced nulls of variable depth. The pattern of changes in echo spectra with orientation for the experimentally measured acoustic returns was very similar to theoretically predicted patterns based on a distorted wave Born approximation (DWBA) model. Information contained in the broadband echo spectra of the krill was exploited to invert the acoustic returns for angle of orientation by applying a newly developed Covariance Mean Variance Classification (CMVC) approach, using generic and animal-specific theoretical and empirical model spaces. The animal-specific empirical model space was best able to invert for angle of orientation. The CMVC inversion technique can be implemented using a generic empirical model space to determine angle of orientation based on broadband echoes from individual zooplankton in the field.L.V.MT.’s research was supported by the Ocean Acoustics, Oceanic Biology and URIP programs of the Office of Naval Research Grant Nos. N00014-89-J-1729, N00014-95-1-0287, and N00014-92-J-1527, the Biological Oceanography program of the National Science Foundation Grant No. OCE-9201264, and the WHOI/MIT Joint Program Education Office