Garmin Fishfinder 100 BLUE Owner's Manual

Also see for Fishfinder 100 Blue: Specifications

30On the WaterOn the Water11223 3Understanding SonarIf you are unfamiliar with sonar, or need help determining what isdisplayed on the chart, then this section may be for you. This sectionis intended to help the novice user gain some understanding of how theFishfinder 100 Blue operates and how it can help improve their fishingproductivity.To understand what the unit is displaying, it is important to have ageneral knowledge of how the unit works and how it determines what todisplay. Briefly described, the unit operates by transmitting sound wavestoward the bottom of a lake, stream or seabed in a cone shaped pattern.When a transmitted sound wave strikes an underwater object such as thebottom, a piece of structure, or a fish, sound is reflected back to thetransducer. The transducer collects the reflected sound waves and sendsthe data to the unit to be processed and displayed on the chart. Theunderwater data is displayed on the chart in the order that it is returned:first returned—first on the chart.The diagram in the sidebar demonstrates this, showing an underwaterscene as it would be displayed on the chart. Generally speaking, if the onlything between the transducer and the bottom is water, the first strongreturn will come from the bottom directly below the transducer. This firststrong return sets the bottom level. Weaker secondary returns provide thedetailed data. Stronger returns will display in darker colors, black beingthe strongest return.Unit Operation and the ChartThis fish is currently in a Dead Zone and is not detectedby the sonar. The fish is in the coverage area of thetransducer, but remember the first strong return sets thebottom level. The fish will never be detected since thebottom level will never be set below the fish.