River Habitat

Fish swim amid a river habitat populated with branches. The double and sometimes triple images of some fish
and branches occur when the objects are near a
placid water surface. The placid surface is an
acoustic mirror. The two and sometimes three
images occur from different round trip times of sound
from the sonar to the object and back to the sonar.
The longer the round trip time, the more range (distance) from the sonar the object appears. The three different round trips are direct/direct, direct/surface bounce,
and surface bounce/surface bounce. Direct means the sound travels directly between the sonar and the object. Surface bounce means the sound bounces off the surface as part of its travel between the sonar and object.

Courtesy of Todd Schwartz,
Fisheries and Oceans Canada,
Manitoba District, Winnipeg Office