I sort of understand the concept although it does not make a whole lot of sense to me I somewhat grasp it now as far as depth. However what should your minds eye use to determine distance out to the side of the boat?
Quote Originally Posted by rnvinc View Post
In a nutshell...what this means is...

Sonar basically measures time...the time it takes for the sound pulse (ping) to leave the xducer, reflect off targets, and return to the xducer...

Then, because the speed of sound in water is constant ....the unit can calculate distance to reflective targets...

If we take a rope just long enough to touch the lake bottom directly under the xducer...(no matter the depth as long as the rope touches the lake bottom)...

Then we tie a ball on 1 end and tie the other end to the xducer...

Then we swing that ball in an arc all the way to the surface to the left...
Then we swing that ball in an arc all the way to the surface to the right...

Any reflective target within that ball's arc (rope included)...would lie in the "dark water column" in the SI image...

The distance from the echo target to it's own shadow is what gives the "mind's eye" the perception of how high in the water column that target actually is...

Notice in both my depictions above, I have drawn fish targets at the same distance from the xducer....because the xducer does not know where in the SI beam shape that target actually is...the unit only knows "how far" that target is from the xducer...therefore the units "paints" both targets directly in line with each other away from the centerline....even tho the targets are at completely different depths in the water column....

The individual shadow of each target is what your "mind's eye" uses to understand how high in the water column each of those target are...

Rickie