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Second Return: The Second Return is a term that describes the appearance of a second
sonar return below the primary sonar return (bottom contour) at exactly twice the true
depth. The second return is caused by the same sonar energy bouncing off the bottom
once, rebounding to the water surface and then traveling back down to the bottom to
be reflected again. Second returns are more common in shallow water and over hard
bottoms; it is actually possible to see a third sonar return under some circumstances.
The second return provides useful information to help determine bottom hardness, as
areas with harder bottoms will generally create a second return. The second return can
be used as a guide to set Sensitivity when in shallower water.
Sensitivity: Sensitivity is a user feature that adjusts the sensitivity of the sonar system
to show more or less detail in the water. Higher sensitivities are often preferred;
however, when the water contains debris (silt, storm debris, etc.) it can be difficult to
pick out targets. Conversely, if sensitivity is set too low, relevant targets may be missed.
SONAR: SONAR is the acronym for SOund and NAvigation Ranging. Sonar technology
uses precision sound bursts transmitted underwater to determine the distance and
other attributes of objects in the water. Distance can be determined because the speed
of sound in water is constant, and the time for the signal to return is measured. Sound
also travels very quickly underwater, making sonar a responsive, cost-effective tool.
Sonar is the basic technology behind all recreational and commercial fishfinding and
depthfinding devices.
Sonar Echo Enhancement: Sonar Echo Enhancement is a Humminbird® feature that
describes the high degree of sonar sensitivity achieved through a combination of
transmitter/receiver and software algorithms. The result of Sonar Echo Enhancement is
to display virtually everything in the water that is of interest to the angler, including bait
fish, game fish, thermoclines, weed beds, subtle structure, and more.
Sonar Update Rate: Sonar Update Rate is the number of times per second that the
transmitter/receiver sends and receives sonar signals. A very fast sonar update rate
collects more information and provides a more detailed image of the bottom, fish and
structure. Many Humminbird® units operate at up to 40 times per second when in single
frequency operation. Due to the limitation of the speed of sound in water, the update
rate begins to slow as depth increases to deeper than 50 feet. In very shallow water (less
than 10 feet), however, update rates as much as 60 times per second can be achieved.
Speed: Speed is the rate at which the boat moves through the water. Boat speed can be
measured as Speed Over Ground or Speed Through Water. Speed Over Ground is
provided by GPS, and is the measurement of the boats progress across a given distance.
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