Author Topic: side imaging coverage range  (Read 2723 times)

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Offline JSI

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side imaging coverage range
« on: March 06, 2015, 07:30:11 PM »
Hi all,  just trying to figure out the concepts of my unit.  Question is about coverage depth of side imaging.  I understand the distance to the sides but what depth does it cover?  I am assuming beam does not go out like a square so I dont understand  the ranges of depths that the unit reads when in side imaging. Seems like there must be a blind spot for shallower water on both sides the farther out it looks.  I hope I am explaining myself thoroughly and appreciate all the help.  thanks.  Joe


Offline rnvinc

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Re: side imaging coverage range
« Reply #1 on: March 06, 2015, 10:30:45 PM »
The "Main Axis" of the left and right SI beams are at about 30░ from horizontal ...(The "Main Axis" is the strongest part of the sound pulse) ...

The sound pulse radiates outward (along the Main Axis and away from the Main Axis) in an ever decreasing sound strength ...

This allows the 455kHz sound pulse to cover from the water's surface (on both sides of the xducer) all the way down and overlapping under the boat ...before the sound pulse diminishes to a strength that wouldn't pick up echoes ...

This is the SI beam form of the right SI pulse ... Add a matching left SI pulse and it's evident that the SI covers a full 180░ under the boat ...



I'm not understanding your question of depth coverage ...


The HB specs for the SI depth is 150ft ... This could be more or less dependent on bottom composition and water borne particulate ...

Rickie
« Last Edit: March 06, 2015, 10:52:07 PM by rnvinc »

Offline JSI

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Re: side imaging coverage range
« Reply #2 on: March 07, 2015, 07:40:51 AM »
Your explanation was perfect and appreciated.  I was not understanding how there were readings all the way to surface the farther you got away from the boat.  Now I understand (I think) as the transducer also projects upward correct?  If so though  what causes the bounce back when signal goes up from main axis  and reaches the surface?  Does the surface cause the return bounce back signal  like the bottom does when signal hits it?  I really appreciate the help.  I believe that the first step in understanding the unit is to fully understand the technology and science of it 1st so this is why I am asking so many questions.  thanks again!  Joe

Offline JSI

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Re: side imaging coverage range
« Reply #3 on: March 07, 2015, 07:45:28 AM »
Now that I think about it thats a dumb question.  surface does not need a return signal.  only objects in the column above the axis needed to be read and they will return the signal.  At least thats my call until someone smarter then I weighs in!!  Thanks again!  Joe

Offline Rickard

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Re: side imaging coverage range
« Reply #4 on: March 07, 2015, 11:30:44 AM »
Hi JSI,
You are right, the surface doesn't need a return signal. This doesn't prevent the surface from returning echoes, though. In wavy conditions and when the transducer is located a few feet below the surface visible returns from waves use to appear. The large difference in acoustic impedance between water and air means sound is reflected by the surface effectively.

Rickard

Offline rnvinc

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Re: side imaging coverage range
« Reply #5 on: March 07, 2015, 09:25:26 PM »
So the SI beams are "thin slice" beams that are very wide top to bottom ... But very thin front to back ...

Every time the unit pings, the sound pulse is sent out in this beam form (Referenced above) to reflect off objects in that "thin slice" beam ...

Then the processor assembles the data from those individual pings into the SI image ... Much like an MRI takes "thin slice" pix of the body and then re-assembles those "thin slices" together to make a "whole body" image ...

Rickie

Offline JSI

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Re: side imaging coverage range
« Reply #6 on: March 08, 2015, 07:17:22 PM »
Thanks for all the help guys!  This is a great forum and wont be my last question.  Joe


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