Why fish arch...Lowrance.com sonar tutorial

Lowrance did a good job putting this together....

Why fish arch....(Lowrance.com sonar tutorial)

The reason fish show as an arch is because of the relationship between the fish and the cone angle of the transducer as the boat passes over the fish. As the leading edge of the cone strikes the fish, a display pixel is turned on. As the boat passes over the fish, the distance to the fish decreases. This turns each pixel on at a shallower depth on the display. When the center of the cone is directly over the fish, the first half of the arch is formed. This is also the shortest distance to the fish. Since the fish is closer to the boat, the signal is stronger and the arch is thicker. As the boat moves away from the fish, the distance increases and the pixels appear at progressively deeper depths until the cone passes the fish.

If the fish doesn't pass directly through the center of the cone, the arch won't be as well defined. Since the fish isn't in the cone very long, there aren't as many echoes to display, and the ones that do show are weaker. This is one of the reasons it's difficult to show fish arches in shallow water. The cone angle is too narrow for the signal to arch.

Remember, there must be movement between the boat and the fish to develop an arch.

http://i477.photobucket.com/albums/r...c/colrmako.gif

Nice!

pretty cool, BUT, how many can get their FF to show complete arches ????

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Originally Posted by jimp

pretty cool, BUT, how many can get their FF to show complete arches ????

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I agree jimp...arches seem to be more voodoo than science....

I hope that the info will give people "technical" understanding of how the relation between the sonar's cone shape and a fish moving thru that cone....creates an arch (elusive as it is)..

In a nutshell...(because sonar knows nothing but "time".....calculated into "distance" ....from an echo)
An arch is created because of the distance from the xducer to the fish:
1. when the fish enters the sonar's cone shaped beam...
2. as the fish passes thru the sonar's cone shaped beam...

Rickie

Noticed they called it SONAR.

That arch could be a stick too. ha

Arches produced by sticks, rocks, and other things tend to have a single color (varying in shade) due to their mostly being constant density.

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Originally Posted by CarolinaJim

Arches produced by sticks, rocks, and other things tend to have a single color (varying in shade) due to their mostly being constant density.

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Yep. But the demo above is not in color and as you know, it depends on the shape of the underwater object too.

Good point on the shape, and drives home the poit of the demo. It is all distance based and shape effects distance. Even in gray scale a fish arch tends to have black center or top for partial arch and gray ends/bottom or sides of arch.

Yep.