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Help my understand SideScan Sonar

Old 01-29-2016, 01:49 PM
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Default Help my understand SideScan Sonar

I've been looking into new fishfinders and a lot of them advertise side scan technology. For some reason I'm having a hard time understanding just what the heck I'm looking at.

Is this basically a birds eye view of the lake/ocean floor? Or is it looking straight out from the boat in the right and left directions?

What exactly is the darkest band in the middle just to the left and right of the vessel's path? I heard it was the open water but that doesn't make sense to me. It's all underwater.
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Old 01-29-2016, 02:05 PM
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So think of it as "butterflying" the normal bottom picture. Your prop is at the very top center of the white middle line. The bottom appears to be about 35' down with the trees sticking up from the bottom (they're pointing towards the center of the page), the rocks/boulders on the right are about 60-80' to the right of the boat (or where the boat was). The darkest band in the middle is the water column (on a normal sounder this is usually the blue field of the screen). Once photbucket gets done with maintenance I'll throw some pics I have of both the downscan and side scan of the same image. Hopefully I didn't make it worse.
Old 01-29-2016, 02:08 PM
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Keep in mind what you are looking at are shadows. The hard lines down the middle are the shadow of the wake trail. Looking almost straight down is underwater growth, plants. To the left and right the bottom has larger objects. Most of what you are looking at is shadow. How long the shadow is will give you and indication how far it extends off the bottom.
Depth of water has a lot to do with the usefulness of this tool. In shallow water the path is very narrow, you are not looking at much. In deeper water this tool comes to life and will open up the unknown for you. Good luck.
Old 01-29-2016, 02:35 PM
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Dang it! The thread title is supposed to say Help "ME" understand not "MY".
Old 01-29-2016, 02:37 PM
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Originally Posted by mahimahi99 View Post
So think of it as "butterflying" the normal bottom picture. Your prop is at the very top center of the white middle line. The bottom appears to be about 35' down with the trees sticking up from the bottom (they're pointing towards the center of the page), the rocks/boulders on the right are about 60-80' to the right of the boat (or where the boat was). The darkest band in the middle is the water column (on a normal sounder this is usually the blue field of the screen). Once photbucket gets done with maintenance I'll throw some pics I have of both the downscan and side scan of the same image. Hopefully I didn't make it worse.

I kind of understand what you are saying but what does a fish show up as if it is suspended midway in the water column at say 20ft, over those boulders to the right?
Old 01-29-2016, 03:02 PM
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https://www.youtube.com/watch?v=oa1-igWNC6c

https://www.youtube.com/watch?v=62allBQil9s






Old 01-29-2016, 03:04 PM
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Originally Posted by mahimahi99 View Post
So think of it as "butterflying" the normal bottom picture. Your prop is at the very top center of the white middle line. The bottom appears to be about 35' down with the trees sticking up from the bottom (they're pointing towards the center of the page), the rocks/boulders on the right are about 60-80' to the right of the boat (or where the boat was). The darkest band in the middle is the water column (on a normal sounder this is usually the blue field of the screen). Once photbucket gets done with maintenance I'll throw some pics I have of both the downscan and side scan of the same image. Hopefully I didn't make it worse.
Well explained
Old 01-29-2016, 03:53 PM
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Originally Posted by bobcat_fisherman View Post
I kind of understand what you are saying but what does a fish show up as if it is suspended midway in the water column at say 20ft, over those boulders to the right?
Yeah, they'll show up in that range or even at the bottom, but they might show up as specs and with the Side Scan it can be hard to tell them from structure. This is why once I find the structure you can split the screen - one side with the side scan/down scan and the other side with the traditional sonar so you can see the fish. Lowrance and Simrad have a feature called Downscan Overlay. That feature will allow you to combine the Downscan and Traditional on the same screen - that way you don't have to split the screen. With the overlay, you can see if a fish is sitting next to structure i.e. a piling, rock or whatever. Here's a good example of the overlay:
The brown items in the top split is the Downscan (structure) the color (orange/blue/yellow) is the traditional sonar overlaid and now you can see what is fish and what is structure. The bottom screen is of the same except in Side Scan (in the blue palate). Try this, take the 1st 3 fingers of your left hand and cover up just the left portion of the blue structure, now look at the right side of the blue structure and visually swing it up (to the left) on top of the top split, if you put that blue box over the top of the brown box it the same image - whew! Hopefully that didn't thoroughly confuse you.

http://www.lowrance.com/Global/Lowra...HORZ-BB-SS.png
Old 01-29-2016, 04:04 PM
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This is a video that really helped me when I was first looking at sidescan. The 3D "folding" of the image is what helped me.

https://youtu.be/yNucS1bniIw

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Last edited by spearfish III; 01-30-2016 at 11:38 AM.
Old 01-29-2016, 06:40 PM
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I found this one of the best explanations for those who don't understand the structure scan display presentation. Skip to 2:30 for the explanation.
https://www.youtube.com/watch?v=Z7MsM-W9Zm4
Old 02-01-2016, 07:35 AM
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Very helpful info!

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