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Lowrance Glossary of Terms for Sonar/GPS
written by Lowrance

A glossary of terms for Lowrance fish finder technology.
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Acquisition Time
Amount of time required for a GPS unit to lock onto 3 satellites to provide a 2D fix (latitude and longitude) of present position.

Actual Sonar Returns
With Advanced Fish I.D.™ off, Lowrance fish finders display actual sonar returns, which show likely game fish targets as fish arches. Actual returns also reveal important underwater detail like thermoclines, baitfish and fish movement.

Advanced Fish Symbol I.D.™
Also called Fish I.D., it's what many anglers say is the easiest way to identify fish targets on their Lowrance units and is ideal for fishing shallow water. With Fish I.D. on, it automatically interprets sonar echos and displays them as fish symbols. The fish symbols are displayed in up to four different sizes to match the relative size of the target echo. With Fish I.D. off, and showing actual sonar returns, targets are displayed as fish arches.

Advanced Signal Processing (ASP™)
Available on all Lowrance fish finders, ASP™ helps you easily spend more time fishing, and less time adjusting sonar sensitivity. With ASP™ on, it automatically fine-tunes your sonar settings for the clearest, most accurate picture of the underwater world. As water conditions change, ASP™ filters out "clutter" that interferes with sonar signals...such as boat speed and suspended particles like algae and plankton...for the best display of fish targets under your boat.

Alarms
Alarms are designed to alert you to certain sonar "events" by sounding tones. With alarms, you don't need to constantly look at the display, so you spend more time fishing. Lowrance features three main types of alarms, and all are selectable on/off by the user.

  • The FISH ALARM alerts you when a fish symbol appears on the screen, with different tones for different sizes of fish targets.
  • The ZONE ALARM lets you set an underwater depth zone (e.g. 21 ft. to 53 ft.) and sounds an alarm tone when targets are detected in that zone.
  • DEPTH ALARMS are triggered only by signals returning from the bottom. Simply set the depths you want - whether Shallow Alarm, Deep Alarm, or both - and the alarm tone will alert you when the bottom goes shallower, or deeper, than your settings.

Altitude (ALT)
Your height above sea level.

Backlight
Selectable on/off illumination that lights both the display and keypad on Lowrance units for enhanced screen viewing when fishing at night and in low light.

Bearing (BRG)
The precise compass direction (in degrees) from your present position to the next waypoint. (Readings are selectable in either degrees magnetic or true north).

Cavitation
The sudden formation and collapse of air bubbles in water due to turbulence. If air bubbles pass over the face of the transducer, the signal from the transducer is reflected back by the air bubbles. These reflections are very strong and will result in noise which will interfere with bottom, structure and fish signals, making them difficult or impossible to see.

Chart Speed
The chart is the picture of the underwater world you see on the display, and the chart speed is how fast that picture moves...or scrolls...across the screen from right to left. This scroll speed is adjustable to help display better fish arches...or to suit your viewing preferences when using fish symbols.

Clock
Your local time.

Cold Start
The process of powering up a new GPS receiver for the first time and having it search out and lock onto the satellites by itself, without the benefit of initialization data. This procedure is slower and may require several minutes for initial satellite acquisition.

COLORLINE™
COLORLINE™ helps separate fish and important structures on or near the bottom from the actual bottom. Since more active-feeding fish hold close to hard bottoms and structures, COLORLINE™ helps you find more potentially productive water quickly. By comparing color and width you can distinguish between a hard and soft bottom.

Count down-timer (DNT)
Starts at a user setting and counts down to zero.  Useful for setting a time limit for travel. Count up-timer (UPT) - Starts at zero and counts upwards. Useful as a measure of elapsed time of travel.

Course Deviation Indicator (CDI)
Shows your distance to the side of the desired course line.

Course Over Ground (COG)
The current direction (in degrees) that you are actually traveling. (Selectable in degrees magnetic or true north)

Cross Track Error (XTE)
Digital reading on GPS steering screens that indicates precisely how far off you are, to the right or left of the center of the course.

Differential GPS (DGPS)
A system devised initially by the U.S. Coast Guard that is now an international maritime standard to improve GPS accuracy levels to be within 10 meters. It employs a land based, fixed position, DGPS reference receiver to first calculate any basic GPS errors (and previously Selective Availability errors). It then transmits the necessary correction factors to mobile GPS receivers in the area. DGPS does require an added beacon receiver to communicate with the standard GPS unit.

Distance (DIS)
Distance remaining between your present position and a waypoint.

Distance To Go (DTG)
Digital readout (selectable in miles, nautical miles, or kilometers) displayed only when navigating to a waypoint. It simply indicates the remaining distance from your present position to the next waypoint.

EGNOS
Refers to a capability found on higher specification GPS and chartplotter units.  This acronym stands for European Geostationary Navigation Overlay Service.  This service augments the American GPS service by reporting on the accuracy and reliability of its signals and as a result increases the accuracy of compatible receivers in the European region to around 1.5 metres.

Estimated Position Error (EPE)
An estimation of the accuracy of your position that tells you how far off target your unit might be. This calculation is based on the geometry and position of tracked satellites, time clock offset, satellite signal quality, and more.

Estimated Time En-Route (ETE)
An estimation of the time required to travel to a pre-selected waypoint or the next waypoint in a route. This calculation is based on the speed and direction of travel towards the selected waypoint.

Event Marker
A graphic symbol that can be placed on the plotter display (and saved in memory) to represent some special event or area of interest to the GPS user. Also known as Icon.

FasTrack™
A selectable on/off feature, FasTrack™ displays flasher-style sonar returns in a narrow vertical column at the far right of the sonar screen. Especially useful for ice fishing or fishing at anchor, FasTrack™ is a standard feature on all Lowrance sonar units after 2001.

Film SuperTwist
Many Lowrance fish finder and GPS/mapping units use this technology for liquid crystal displays (LCD). Film SuperTwist provides excellent contrast and readability...in direct sunlight or with the backlight for fishing at night or in low light...and from virtually any viewing angle. Lowrance Film SuperTwist screens are also easy to see with polarized sunglasses.

Fish Arches
With Advanced Fish I.D.™ off, Lowrance sonar units display underwater fish targets in the shapes of "boomerangs" or fish arches. As with fish symbols, the larger the return echo of the suspended fish target, the larger the fish arch. To learn how fish arches are created, go to the Lowrance sonar tutorial.

Fish Symbol I.D.™
See Advanced Fish Symbol I.D.

FishReveal™
When viewing actual sonar returns, the unique FishReveal™ feature is what you need to expose fish targets hiding in underwater cover -- like surface clutter, thermoclines, and weed beds -- with 10 levels of gray tones that are adjustable for the most revealing look in virtually any underwater environment.

FishTrack™
When using Advanced Fish I.D.™, and with FishTrack™ on, the digital depth is displayed directly above each fish symbol. Many Lowrance anglers find FishTrack™ helpful in making quick and precise lure presentations to the correct depths.

Fix
A measure of your receiver's position quality. A fix of 1 is poor, 9 is best.

FlashGraf™
FlashGraf™ combines a scrolling sonar target graph with a digital LCD flasher with GRAYLINE® or COLORLINE™. This allows you to view two of the most popular ways of finding fish all in one screen. FlashGraf™ also employs the "Resize Window" feature, which allows you to make the sonar graph or flasher "window" wider or narrower in the split-screen display according to your preference. Also, the "Overlay Data" feature is included to allow temp, speed, lat/long, and more information to be displayed in the flasher "window".

FloatDucer™
This is a unique, floating transducer you can use when fishing off a bank, shore, bridge or dock. Shaped like an odd-looking UFO, just toss the FloatDucer™ onto the water with its 50' cable connected to a fixed-mount or portable Lowrance sonar. FloatDucer™ provides an effective wide-angle underwater coverage area of up to 60 degrees with ASP™ on.

Global Positioning System (GPS)
The Global Positioning System (GPS) is a "constellation" of 24 well-spaced satellites that orbit the Earth and make it possible for people with ground receivers to pinpoint their geographic location. GPS location accuracy is within 20 meters. Location accuracy can be boosted through the use of Wide Area Augmentation System (WAAS) or Differential GPS (DGPS). The GPS is owned and operated by the U.S. Department of Defense but is available for general use around the world.

GRAYLINE®
This patented Lowrance feature helps you distinguish between hard and soft bottoms, where the thicker the gray band, the harder the bottom. GRAYLINE® also helps separate fish and important structures on or near the bottom from the actual bottom. Since more active-feeding fish hold close to hard bottoms and structures, GRAYLINE® helps you find more potentially productive water quickly.

Ground Speed (GS)
Your actual speed; your speed relative to the ground being traversed in a given amount of time.

HyperScroll™
HyperScroll™ feature locates and displays fish targets at higher boat speeds with increased soundings per second.

Icon
A graphic symbol that can be placed on the plotter screen (and saved in memory) to represent some special event or area of interest to the GPS user. Also known as Event Marker.

Initialization
Refers to the procedure of telling a new GPS receiver where it is, when it is turned on for the first time. Information required for initialization includes approximate present position in latitude/longitude coordinates, the current local time and date.

Magnetic North
Magnetic north is the location our compasses point to; it lies several hundred miles to the south of true north, at a location in Canada.

Map Datums
Since the earth is not flat a method must be used to create a "flat map" from a round earth. Maps and charts are based on a survey of the area that's covered by the map or chart. These surveys are called "Datums". Maps that are created using different datums will show the same latitude/longitude in slightly different locations. Different datums are based on different mathematical models of the earth's shape and dimensions (ELLIPSOIDS) plus an additional factor of PROJECTION.

MGRS (Military Grid Reference System)
An alphanumeric version of a numerical UTM (Universal Transverse Mercator) grid coordinate.

MSAS
Refers to a capability found on higher specification GPS and chartplotter units.  This acronym stands for Multi-functional Satellite Augmentation System.  Based in Japan, this service augments the American GPS service by reporting on the accuracy and reliability of its signals and as a result increases the accuracy of compatible receivers in the area surrounding the east coast of Asia to around 1.5-2 metres.

Multiplexing Receiver
GPS receiver that rotates a small number of channels to multiple satellites in order to provide current positioning data. Typically, multiplexing receivers require more time for satellite acquisition and lock on, and are not as accurate as parallel channel receivers. Multiplexing receivers are also more prone to lose satellite fix in dense woods compared to parallel channel GPS receivers.

Noise
Noise is visual "clutter" that appears on the display. It's caused by too many undesirable signals being picked up by the fish finder (typically from electrical sources such as trolling motors, alternators, spark plugs, radio transmitters, etc.) Manually adjusting the sensitivity helps fine-tune the sonar to show the most detail with the least noise. For automatic sensitivity adjustments for the best picture possible, Advanced Signal Processing (ASP™) is also found on all Lowrance units.

Output Power
The amount of electrical energy applied to the transducer by the sonar transmitter. Expressed in watts, typically the higher the output power the sonar unit has, the deeper it can penetrate, and the finer the detail that can be shown.

Parallel-Channel Receiver
GPS receiver that simultaneously tracks multiple satellites to provide the fastest, most reliable and accurate navigational data...under the severest of environmental conditions.

Peak-to-Peak
Normally used to describe the output power of a sonar transmitter. This value is a measurement of the total swing of an AC voltage from its peak negative value to its peak positive value.

Pixels
These are "picture elements," or little squares of color that come together to form shapes and images on a liquid crystal display (LCD). The more pixels per square inch, the sharper and more detailed picture you see.

Plotter Display
Provides an overhead "bird's-eye" view of your current position, relative to the waypoints and event marker/icons you've saved. A dotted-line marks the shortest route to the chosen waypoint, and a recorded plot-trail indicates the path you've taken so far.

Position Display
One of the primary navigational data screens that emphasizes the present position latitude/longitude coordinates, as well as other helpful information.

Present Position
Current location on the face of the Earth, in terms of the specific latitude/longitude coordinates, displayed in degrees/minutes/& thousandths of a minute.

Programmable Windows
The ability to customize existing split-panel window groupings with the specific combination of navigational data preferred.

Pulse Length
The length of time a sonar unit transmits a pulse of sound into the water. Sometimes referred to as Pulse Width.

Range
Range is the depth of the water column - from the surface down - displayed on the sonar screen. Lowrance units will automatically adjust the range to keep the bottom (and depth shown in feet or meters) displayed in the lower part of the screen. There's also a manual mode where anglers can select the range they want to view from a menu of depth choices.

RMS
Literally "root mean square." A DC voltage that will produce the same heating effect (power output in Watts) as the AC voltage. For a sine wave, the RMS value is equal to 0.707 times the peak value of an AC voltage. Example: divide Peak-to-Peak by 2 (or in half) and multiple by 0.707 = RMS voltage.

Route
Consists of two or more waypoints combined in a course of travel. It provides the automatic capability to navigate through several waypoints, without having to reprogram the unit after arriving at each one. Once programmed into the GPS unit, the route provides the option of navigating forward through the waypoints or in reverse order.

Satellite Status Display
An information screen that shows technical data about each satellite in view. Information includes receiver channel numbers; actual satellite I.D. numbers; status of satellite tracking (T) or searching (S); satellite elevations and azimuths; signal-to-noise ratios (higher the number, the better); and dilution of precision ratings (GDOP is most important; smaller the number, the better).

Savable Plot Trails
The capability to save the actual trail created on the plotter display, thereby enabling the GPS user to either backtrack the course immediately...or retrace the trip at a later time.

Selective Availability (S/A)
The system used by the U.S. Department of Defense prior to May 1, 2000 to intentionally degrade the accuracy of satellite GPS signals being transmitted to civilian GPS receivers. Until recently, all brands of civilian GPS receivers were equally affected by S/A. With random S/A on, the government had agreed that civilian GPS accuracy levels would consistently be 100 meters or less, 95% of the time. Now that S/A restrictions have been lifted, accuracy levels have improved to 20 meters or less.

Sensitivity
This is a manual adjustment that allows users to fine-tune the fish finder to see the most underwater detail with the least visual noise. For anglers who'd rather spend more time fishing than adjusting, Advanced Signal Processing (ASP™) does this automatically, and is a feature of all Lowrance sonar units.

Skimmer®
Available in a variety of operating frequencies, Skimmer transducers feature a low profile for high-speed performance...even up to 70 mph! The patented design helps prevent cavitation and other interference that affects sonar performance. Finely tuned to provide exceptional echo sounding, transom-mounted models feature a kick-up bracket for protection against impact with debris and obstructions.

Speed/Temp
Using special sensors, Lowrance units can digitally display surface water temperature, boat speed and distance log (odometer) in addition to showing the depth range. Serious anglers, especially tournament pros, use speed and temperature information as aids in their fishing strategies. Note: displaying speed is used solely for trolling purposes, and does not work at "top-end" boat speeds.

Speed Over Ground (SOG)
Digital reading that indicates your current ground speed. (Selectable in miles-per-hour, knots, or kilometers-per-hour)

Steering Screen
Shows a graphic, "highway view" of the GPS user's Course Over Ground. Provides helpful instructions as to how far off-course...which direction to steer, right or left, to make corrections...and displays related nav-data pertaining to the waypoint.

Straight Line Navigation
The standard method of navigation used by recreational GPS products. When commanded to navigate to a waypoint, the unit draws a straight, dotted line from the present position to the selected waypoint. It's the shortest, most direct route to the destination. Caution: Straight line navigation does not take into account any obstacles in the path; interim waypoints may be required to navigate safely around obstacles.

Structure
Structure is basically all solid objects rising from the bottom of a lake or river that isn't part of the actual bottom...like sunken trees, brush and rock piles...which creates habitats, feeding grounds and cover for game fish. For locating and separating close-holding fish from structure, GRAYLINE® is the preferred choice of more anglers.

Thermocline
These are areas underwater where warmer layers of water meet cooler layers, and where fish are often active. Generally, baitfish hang just above the thermocline, while larger game fish are found suspended in or just below it. Lowrance units will display thermoclines when used in the manual mode, showing actual sonar returns, and with the sensitivity set correctly.

Time To Go (TTG)
Digital reading showing the time remaining from your current position to the next waypoint. This function takes into account your Distance To Go (DTG), and your Velocity Made Good (VMG) to give you as closely as possible the amount of time left to reach your waypoint. Displayed in hours, minutes, and seconds, it will continue counting down until waypoint is reached.

Track (TRK)
The direction you are traveling.

Transducer
The part of the fish finder that functions like an antenna to send out sonar signals (sound waves) and receive return echoes that are displayed as pictures on the sonar screen. Lowrance transducers can be attached to the transom or inside the hull of a boat, or even to a trolling motor using a special mounting.

True North
True north is the top of the world, where all lines of longitude converge; not to be confused with magnetic north.

Turboview
An exclusive HDS built-in graphics engine delivering seamless zooms and 2D-3D chart displays, real-time 3D map navigation data overlay, striking depth in 2D and 3D views, plus high-speed panning/zooming with detailed aerial views for all Platinum chartcards.

UTC
Coordinated Universal Time. Time at the prime meridian at Greenwich, England. Formerly known as GMT.

UTM (Universal Transverse Mercator)
Universal Transverse Mercator (UTM) coordinates define two-dimensional, horizontal positions. Each ZONE in UTM is given a number from 00 to 59 starting at the International Date Line and progressing east. UTM also divides each zone horizontally as well. These divisions start at the equator and are 8 degrees wide. The first half of the alphabet is used for the Southern Hemisphere while the second half is used for the Northern Hemisphere. Thus a point just above the hemisphere would be the letter N proceeding to the letter X at the north pole, while just below it would be an M and proceeding backwards to the letter C at the south pole.

Velocity Made Good (VMG)
Digital speed reading, similar to Speed Over Ground (SOG), that compensates for progress being made toward a waypoint. For example, when traveling directly on course toward a waypoint, the SOG and VMG readings may match. However, when traveling off course, the VMG reading will typically be slower than the SOG. VMG is a true indication of the speed being made to the selected waypoint.

Volts
Electrical system voltage.

Waypoint
Location, spot, or destination (latitude/longitude) that can be stored in memory to be recalled and used at a later time for navigation purposes. Simply think of it as an electronic address.

WAAS (Wide Area Augmentation System)
A satellite navigation system designed by the U.S. Federal Aviation Administration (FAA) to boost the accuracy of GPS satellite navigation. Improvements in accuracy are approximated to be within 7 meters. Note: Currently, WAAS is not fully implemented. It was created for aviation applications. It uses geostationary satellites over the equator, which makes WAAS signals easily blocked in North America by terrain obstructions. Users may experience temporary loss of WAAS support, especially in wooded areas.

Zoom
With zoom, you can enlarge the Lowrance sonar or GPS map display for a closer look at small detail and fish target signals. In the sonar automatic zoom mode, the bottom is constantly tracked and displayed in the lower portion of the screen (also called "zoom bottom track"). In the manual zoom mode, you can create a zoom "window" of any size, and move it anywhere up or down in the sonar water column...it doesn't remain locked on to display the bottom.

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