Midfrequency backscatter imaging of fish schools in a shallow water waveguide.

Abstract

In this experimental effort, field data and modeling are used to investigate backscatter imaging of schools of pelagic fish in a shallow water oceanic waveguide. Two-dimensional (2-D) circular images of an oceanic waveguide are created using a monostatic circular receiving array and vertical line array source (12 kHz) deployed from a stationary ship. Horizontal multibeam images of a radial (depth integrated) cross section of the ocean are formed with targets and reverberation structure observed at ranges up to several Km. Examples of waveguide images are presented for data taken in the Puget Sound of Washington state. In some instances, the backscatter from aggregations of fish was observed to be higher than the reverberation; in other cases, fish schools could not be resolved. Fish school locations were independently observed by vertical echo sounding. Preliminary experimental results are shown to illustrate the potential of resolving the 2-D horizontal structure of aggregations of fish using such methods. Modeling is used to interpret the effects of waveguide propagation on imaging. Operational issues related to using waveguide imaging for fisheries’ research and signal processing issues related to waveguide imaging will be discussed. [Work funded by NOPP with support from ONR and NOAA-OE.]