Understanding The Graph - Garmin GPSMAP 178 Owner's Manual

Understanding the Graph

It is important to understand that the unit does not display a 3-D representation of the underwater
environment. The unit can display multiple things at the same time, but cannot determine where the
return originated – only when it was received.
Examples 1 and 2 provide a look at the underwater world from a top view, and illustrate how these
views would be displayed on the graph. On both graphs it appears the fish and tree are side by side as
shown in Example 1. However, when we look at Example 2, we see that the fish can be several feet from
the tree. It is important to remember that the sonar cannot determine where in the coverage area the tree
or fish are, only that the returns were received at the indicated depths in the same time frame.
Enlarged
Transducer
View
Example 1.
Enlarged
Transducer
View
Branches
Fish
Branches
Fish
Example 2.
Appendix G
Understanding the Chart
F
Remember that the sonar displays a 2-D picture of the
underwater environment. The fish and tree could be
located anywhere in the coverage area at that time.