Garmin GPSMAP 2006 Owner's Manual & Reference

Also see for GPSMAP 2006: Declaration of conformity Declaration of conformity Installation instructions Owner's manual Install guide

88Understanding SonarAppendix H Understanding SonarIf you are unfamiliar with basic sonar, or need help determining what is displayed on the graph, thissection may be for you. This section is intended to help the novice user gain some understanding of howthe GPSMAP 2006/2010 operates when combined with a GSD 20 Sonar Module and how it can helpimprove their fishing productivity.To understand what the unit is displaying, it is important to have a general knowledge of how theunit works and how it determines what to display. Briefly described, the unit operates by transmittingsound waves toward the bottom of a lake, stream, or seabed in a cone-shaped pattern. When a transmit-ted soundwave strikes an underwater object such as the bottom, a piece of structure, or a fish, sound isreflected back to the transducer. The transducer collects the reflected sound waves and sends the data tothe unit to be processed and displayed on the graph. The underwater data is displayed on the graph in theorder that it is returned: first returned—first on the graph. The diagram to the left demonstrates this byshowing an underwater scene as it would be displayed on the graph. Generally speaking, if the only thingbetween the transducer and the bottom is water, the first strong return will come from the bottom directlybelow the transducer. The first strong return sets the bottom level. Weaker secondary returns provide thedetailed data. Sonar returns display as reds (strongest), then oranges (strong), yellows (medium), greens(weaker), and blues (weakest) on color models and dark (strongest) to lighter (weaker) shades of gray onmonochrome units.That is a brief description of how your GPSMAP 2006/2010 operates when combined with a GSD 20Sonar Module. The following pages will show how this data can help you to improve your fishing.This fish is currently in a dead zone and is notdetected by the sonar. The fish is in the coveragearea of the transducer, but remember– the firststrong return sets the bottom level. The fish willeventually be detected when the first strong returnsets the bottom level below the fish.