Author Topic: bait on 2d vs DI  (Read 3091 times)

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Offline gspn

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bait on 2d vs DI
« on: January 05, 2015, 08:56:58 PM »
This is a side-by-side screen capture where the DI picked up bait balls with amazing clarity...and the 2D seems to have missed a huge amount of them.  What do you think is causing the difference in these DI and 2D images?  Is 2D always inferior when it comes to finding bait balls?


di 2d diff by scarfam, on Flickr


Offline rnvinc

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Re: bait on 2d vs DI
« Reply #1 on: January 06, 2015, 01:39:32 AM »
I think the 2d and DI in your shot are a good representation of normal returns of bait ...

The imaging frequencies for DI are much higher than the frequencies used for 2d ...

Higher frequency renders greater detail by design ...

Rickie
« Last Edit: January 06, 2015, 01:42:58 AM by rnvinc »

Offline rnvinc

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Re: bait on 2d vs DI
« Reply #2 on: January 06, 2015, 01:41:38 AM »
I'm curious as to why you are running the Lower Depth setting in manual 49' ...

Are you intentionally wanting to see the double echo in the 2d view ...??

Rickie

Offline gspn

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Re: bait on 2d vs DI
« Reply #3 on: January 06, 2015, 08:39:25 AM »
I'm glad you asked...because I had no idea I was doing that!   ;D  I'm still pretty new to the gear.  I do not want to see a double echo.  I'll dig around in the settings and see if I can change it.  Thanks!

Offline Humminbird_Greg

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Re: bait on 2d vs DI
« Reply #4 on: January 06, 2015, 09:22:30 AM »
You cannot make an apples-to-apples comparison between the 2D sonar and the Di sonar due not only to the frequency used but also due to the different shape of the transducer beam(s) used.  The 2D sonar is looking straight downwards and is conical in shape (circular where it would contact the bait ball) but the Di sonar in the Si units comes from the left and right Si sonar data which tells me that school of baitfish were stretched horizontally under the boat.  Since the Si beams are very thin front to back but very wide left to right, they can show this where the circular beam of the 2D sonar cannot. Also some of the baitfish may not have been within the 2D sonar beam but were within the left and right Si sonar beams.  Of course some of the width of the Di sonar can be manipulated by the Down Imaging Beam Width menu setting.
Greg Walters at Humminbird
gwalters@johnsonoutdoors.com

Offline gspn

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Re: bait on 2d vs DI
« Reply #5 on: January 06, 2015, 10:07:34 AM »
Great info!  That's exactly the type of info I need to start learning to decipher what the machine is telling me.  Thanks Greg.

Offline rnvinc

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Re: bait on 2d vs DI
« Reply #6 on: January 06, 2015, 07:51:52 PM »
I'm glad you asked...because I had no idea I was doing that!   ;D  I'm still pretty new to the gear.  I do not want to see a double echo.  I'll dig around in the settings and see if I can change it.  Thanks!

The "Lower Depth" menu choice is in the Xpress menu (1 Menu button press) ...

*Auto will keep the bottom on the screen ...
*Manual can be used to make more efficient use of the display vertical resolution ...
*Manual can also be used to see the "double echo" ...like in your image ...

Some guys like seeing the "double echo" ...a strong "double echo" (like your image) is indication of harder bottom ... Allowing the sound pulse to effectively reflect off the bottom ... Then reflect off the water surface ... Then reflect off the bottom a second time ... And then received by the xducer ...

Rickie
« Last Edit: January 06, 2015, 07:55:10 PM by rnvinc »


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