Glossary | Sonar Terms |
Power Output The amount of sound energy emitted into the water by the transducer’s transmitter. Power output is measured using either RMS (Root Mean Square) or
Pulse Width (Pulse Length) The length of time that a sonar sound burst is transmitted into the water. Shorter pulse widths provide better target separation, but cannot travel to great depths. Longer pulse widths provide better depth penetration, but result in poorer target separation. Humminbird® varies pulse width based on depth to optimize both target separation and depth performance. See Target Separation.
Second Return 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 watersurface 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 possible to see a third sonar return under some circumstances. The second return provides useful informationto 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.
SONAR (SOund and NAvigationRanging) Sonar technology uses precision sound bursts transmittedunderwater to determine the distanceand other attributesof 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,
Sonar Update Rate The number of times per second that the transducer’s transmitter/receiver sends and receives sonar signals. A very fast sonar update rate collects more information and provides a more detailedimage 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 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. Speed Through Water is provided by a speed paddlewheel, and is the measurement of the flow past the boat, which may vary depending on current speed and direction. Speed Through Water is most critical for anglers using downriggers, as it impacts the running depth of the down riggers. Speed Over Ground is optimal for navigation, as accurate destination times can be derived from this measurement. Humminbird® products allow for input and display of both sources.
Structure A general term for objects on the bottom that present a discontinuityand are a likely attractor for fish. This includes bottom contour features
Surface Clutter A phenomenon where sonar returns are reflected off of tiny objects near the surface of the water,including algae and even air bubbles.Typically,saltwater environments have significantly greater surface clutter than freshwater due to continuous wind and wave action that causes aerationat the surface.
Target Separation The measurement of minimum distance that a fishfinder needs to be able to recognize two very close objects as two distinct targets (i.e. two fish hanging very close, or a fish hanging very close to structure). Humminbird®fishfinders
145 | Glossary - Sonar Terms |