Dual and Down Imaging
See Fish Finders
Similar to a photocopier, a down imaging finder casts a beam straight down, scanning the area directly underneath your boat and beaming back a 2-dimensional representation of what it sees. Finders that offer dual imaging will also scan the area on the sides of your boat. These finders will provide additional details to help you reach your goal, including what depth things are at and the temperature of the water.