Garmin GPSMAP 296 Pilot's Guide - Page 136

SETTING UP AND USING SONAR > UNDERSTANDING SONAR Understanding Sonar The transducer mounted on your vessel transmits sound waves toward the bottom of a lake, stream, or seabed in a cone-shaped pattern. When a transmitted sound wave strikes an underwater object-such as the bottom, a piece of structure, or a fish-sound is reflected back to the transducer. The transducer collects the reflected sound waves and sends the data to the GPSMAP 296 to be processed and shown. The underwater data is shown on the Sonar screen in the order that it is returned: first returned is the first on the screen. Understanding the Sonar Display One of the first things to understand about sonar is that the transducer sends a beam down to the bottom of the water, much like the beam of a flashlight. The beam starts small near your vessel and expands as it gets to the bottom. Refer to "Transducer Coverage" for more detailed information. The Sonar Page does not show a three-dimensional representation of the underwater environment; the screen is in two-dimensions, much like if you took a picture of an aquarium. Only the depth of the item in the water is shown. The Sonar Page does not show you where an item is located horizontally in the water, as shown in the drawings below. The fish is not directly above the tree in reality, but it can look like it is on the Sonar Page. Sonar Page Generally speaking, if the only thing between the transducer and the bottom is water, the first strong return comes from the bottom directly below the transducer and sets the bottom level. Weaker secondary returns provide the detailed data. Stronger returns screen in darker colors, with red being the strongest return. 128 Fish 1' 10' Tree Tree 20' Aerial View of the Water Sonar Page GPSMAP 296 Pilot's Guide