Figure 10. Acoustic backscatter ambit of a 256-mm alewife at 38 kHz. Distance from the center of the axes represents backscatter amplitude. Backscattering amplitude is color coded with highest amplitude as red and lowest amplitude as blue. Insonifying angle resolution is 20 in the tilt plane (head-tail) and 20 in the roll plane (dorsal-lateral-ventral). The ambit graphically depicts predicted echo amplitude over all degrees of fish orientation. Echo amplitudes are greatly reduced at head-on and tail-on aspects. Maximum amplitudes are at lateral incidences. Maximum dorsal amplitude occurs when the swimbladder is parallel to the incident wave front, which tilts the fish approximately 120 head down.
