SONAR (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 s ignal to r eturn i s me asured. So und also travels v ery q uickly underwater, makingsonar a responsive,
Sonar Update Ra te The num ber of times per second that the transducer’s transmitter/receiversends and receives sonar signals. A very fast sonar updateratecollects more informationand provides a more detailed image of the b ottom, 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 orSpeed Through Water. Speed Over Ground is provided by GPS, and is the measurement of the boats progress across a given distance. Speed Through Wateris 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 impactsthe 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 discontinuity andare 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 s urface of the water , inc luding alg ae and eve n air bubb les. Typically, saltwater environments have significantly greater surface clutter than freshwater due to continuous wind and wave action that causes aeration at 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 clos e to structure). Humminbird® fishfinders provide a v ery good 2 1 /2 inches of ta rget s eparation in shallower than 100 f eet of depth. Target separation decreasesas depth increases due to the need for longer Pulse Width to achieve greater depth. See Pulse Width.
111 | Glossary |
