Humminbird 998c SI - Manual (Page 156)

146
Glossary Sonar Terms GPS & Navigation Terms
provide a very good 2 1/2 inches of target separation in shallower than 100 feet of
depth. Target separation decreases as depth increases due to the need for longer Pulse
Width to achieve greater depth. See
Pulse Width .
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.
Acquisition Time The length of time that a GPS receiver typically takes to determine
a position from at least three satellites. Humminbird® GPS receivers provide very fast
acquisition times (under one minute), permitting users to get out on the water faster.
Altitude The height measurement above sea level. Altitude is a measurement that
can be provided by GPS.
Bearing (BRG) The direction to a destination waypoint measured in degrees from
North (i.e. 321°, where 000° is North, 090° East, 180° is South, 270° is West).
Chartplotter A navigation device that shows Present Position on a Map, along with
Tracks, Waypoints, and Routes. All Chartplotters are also considered Trackplotters.
Cold Start The procedure that a GPS receiver must perform when it does not have
historical information regarding its current location. This procedure typically lasts for
several minutes, and may be experienced upon first power up of the receiver, or if the
receiver has been moved a great distance.
Course Over Ground (COG) The current direction the boat is traveling measured in
degrees from North (i.e. 321°, where 000° is North, 090° East, 180° is South, 270° is
West). When the Course Over Ground is equal to Bearing, the boat is said to be “On
Course” and will arrive at the destination in the most efficient manner. COG is often
confused with Heading. See
Heading .
Cross Track Error (XTE) The straight-line distance of the boat from the intended
Track. XTE measures how far the boat is off course and also triggers the Off Course
Alarm. See
Track .
Differential GPS (DGPS) A system used to improve the position accuracy of the
Department of Defense GPS through the use of secondary “correction signals”
broadcast from ground stations around the coastal United States and on some inland
waterways. These correction signals are provided by the USCG and received by an
auxiliary Differential Beacon Receiver (DBR) that connects to the GPS receiver. The
Glossary - Sonar Terms, GPS & Navigation Terms