A Sonar Phenomena: Simultaneous Returns
Figure 1 shows two Atlantic Sturgeon that appear to be semi-transparent. It appears one can see the bottom texture through the fish. Figure 2 is a drawing showing the vertical angle of the beam with an arc showing an equal range from the sonar. This arc hits the fish (circle) and the bottom at the same time. Returns from the fish and from the bottom return to the sonar at the same time and the display superimposes these returns at the specified range. Reducing the tilt of the sonar and lowering the sonar nearer the bottom will reduce the brightness of the bottom return and make the fish image more opaque. The fish image will be totally opaque when the bottom and fish returns do not overlap in time.
 Figure 1: "Semi-Transparent" Atlantic Sturgeon |
 Figure 2: Beam Diagram |