Humminbird Side Imaging Forums
General => General Discussion => Topic started by: staoB regnaR on June 24, 2012, 10:19:49 PM
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I side imaged the Grand Glaize bridge this weekend and this is one of the pilings. My side imaging works good on other stuff ( I was able to see suspended bait fish, and bass sitting underneath them by a wave breaker. I could even see the metal cable going all the way to the bottom holding it in place) but why do these pillars look so bad? What is the problem with this, it looks like a terrible splotchy patch of nothing. I must say it looks a little worse on Humviewer as well
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staoB regnaR
When you get to this part of the recording again, right click on the SI image.
At the bottom of your choices is " crop to ". Change it from 285' to 148' and see if it doesn't look better.
Mike
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Thanks, here it is at 148'
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staoB regnaR
I would have thought the image would have looked better.
The transducer looks level because the pillars aren't tipped toward the top or bottom of the image.
Hope Greg or someone else has some input.
Mike
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I have found vertical bridge pilings to be very difficult to SI....especially if the boat is moving at an average speed of 2-5mph...
I think this is because the xducer passes by the piling so fast that not enough "pings" actually get to reflect off the vertical structure...
I have learned when SI'ing vertical bridge pilings to speed my chart up significantly...(which is probably just creating an "optical illusion" of the bridge piling on the SI image by "stretching" the few successfully reflected sonar pings across the screen into an image that "looks" more like a bridge piling)...
It seems to work in theory and application...(but I'm not 100% sure of my reasoning)...
I will try and get snapshots next time I am fishing in that area ...
Rickie
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Maybe it matters that most of those bridge pilings are round so just a small part of the signal gets reflected directly while mosts parts of the signal get reflected in different directions ? Also the increased water current around bridge pilings might increase a "mirror effect" of having less signals reflected directly ?
Just my idea as lots of round bridge pillings have some "ghost" appearance on SI.
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When we see bridge pilings they are usually a small target with the shadow behind it.
Round pillers are not as sharp as square pillars.
Chuck
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Thanks guys, that makes sense that only a small part is actually getting back to the boat. On a side note, I did manage to find a large school of crappie near one of the pillars, but I didn't make a recording of it.