Humminbird 561 - Manual (Page 82)

75 Glossary
Thermoclines Water layer(s) of distinctly different temperatures that create a sonar
reflection due to the density of the differing water temperatures. Typically a thermocline will
appear as a continuous band across the display at some distance above the bottom contour.
Thermoclines are of interest to anglers because fish will suspend above or below the
thermocline as they seek the optimum temperature and oxygen levels.
Time Variable Gain (TVG) A processing step applied to the sonar return to “normalize“
the data so that objects of equal size (i.e. fish) appear to be the same size, even if they are
separated by a good distance.
Transducer The transducer is part of the sonar system, which mounts on the boat and is
in contact with the water, that converts the electrical energy from the transmitter into
sound energy, and that forms the sonar beam in turn. Internally, the transducer consists of
one or more piezo electric disks that expand by very minute amounts to create the sound
wave. This element also works in reverse, converting the returned sound energy back into
an electrical signal that the receiver interprets. See SONAR.
Zoom A feature that focuses on a smaller area of the bottom to provide enhanced
resolution. With enhanced resolution, the angler can more easily see fish hanging in
structure or multiple fish hanging close together.
Zoom, Bottom Lock Bottom Lock Zoom is a feature that focuses on a smaller area just
above the bottom to provide enhanced resolution. Unlike regular zoom, it continuously
graphs the bottom at a constant point on the display regardless of changes in depth. This
“flattens“ out the bottom contour, but is effective at showing fish on or near the bottom,
and is preferred by many saltwater anglers.