Topic 10 - Weak return echo
The transducer mounted on the underside of the boat transmits ultrasonic waves or 'pulses' that travel down to the seabed. As the sound waves travel through the water, they scatter and gradually lose strength. When these sound waves hit either fish or plankton, they will bounce back up to the transducer. The shape generated by a single fish and a fish school varies greatly, but when ultrasonic waves hit a fish school they will bounce back in all different directions. Parts of these reflected ultrasonic waves from the fish school will return back to the transducer under the boat. If the distance to the seabed is 100 meters or less, the echo from the seabed will be much stronger than any fish schools in between.
The reflected ultrasonic waves from the fish school will scatter on their way back to the transducer making the signal very weak. This faint signal gets picked up by the element inside the transducer, which in turn sends the information to the main unit of the fish finder. The transducer of a fish finder is a comparatively small thing, measuring only about 7-10 centimeters in diameter for normal recreational vessels. Even though this diameter is small, this is the area that receives the ultrasonic waves returning all the way from the seabed.
The reflected ultrasonic waves from the fish school will scatter on their way back to the transducer making the signal very weak. This faint signal gets picked up by the element inside the transducer, which in turn sends the information to the main unit of the fish finder. The transducer of a fish finder is a comparatively small thing, measuring only about 7-10 centimeters in diameter for normal recreational vessels. Even though this diameter is small, this is the area that receives the ultrasonic waves returning all the way from the seabed. What makes this job hard for the fish finder is that there is a lot of noise in the water, and the echo from a fish is very weak. Out of all the noise that gets generated by pollution, air bubbles, plankton and more, the fish finder has to discern the reflected ultrasonic waves from a fish school. This is especially true when it comes to fish schools that stay close to the seabed. There is a lot of noise and it can be hard to discern what are fish schools and what are not. At times like these, the built in noise removal functions in a fish finder can come in very handy.
