Three-dimensional visualization of fish morphometry and acoustic backscatter

Theoretical acoustic models of fish are used to explain variability in backscatter measurements, improve estimation of target size, and improve target recognition and discrimination among acoustic targets. Acoustic backscatter models that incorporate fish morphology potentially provide more realistic predictions of echo amplitudes than models that approximate morphology using simple geometric shapes. Procedures to obtain digital representations of a fish's body and swimbladder are presented. These digital images are used in a Kirchhoff ray-mode model to predict backscatter amplitude as a function of fish length, acoustic frequency, and angle of insonification. Backscatter amplitude can be displayed as one-dimensional curves, two-dimensional response surfaces, and a three-dimensional backscattering surface (i.e., ambit).