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TOPIC: How to avoid black holes in sidescan?

How to avoid black holes in sidescan? 1 year 11 months ago #10500

  • MarsArtis
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Using an old Macbookpro, so no hardware acceleration.

1- do the lack of HW acceleration affect the quality of Sidewiew mosaic expecially along curvatures?

2 - I'm moving on a seaside coast that never goes deeper than 15m. I'm logging setting the range to 20m. Is this correct and suitable for the RM workflow? The sidescan(L+R+water column on the lower right side) view seems pretty clear to me but the sidescan with removed water column is not as desired. I can see a lot of holes, many black and many others that seems to not really reflect the actual boottom.
What should I better tune?
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How to avoid black holes in sidescan? 1 year 11 months ago #10501

  • MarsArtis
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Side note:
as you can see the bottom has very varying depths along the track, from -1 to -12 back to - 2 meters.
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How to avoid black holes in sidescan? 1 year 11 months ago #10503

  • Team Colibri
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As for range on sidescan I would use 5-8 times depth as range with Totalscan (as well as with LSS-2) as a rule of thumb. But you seem to have issues with picture-quality here tha leads me to say we should look at how your ducer is mounted, because that image is very far from what it can be.

Do you have any photos of how your Totalscan is mounted? Idelly 2-3 photos, one from the side showing the angle towards the hull. One straght from the back and one from the back but sligthly low so we see the hull in front onf the ducer.

This is where you want to be:

Sorry the text on the image is in Norwegian, but here you clearly see small rocks, gravel, some timber and a pipeline. This is from freshwater though, and taken with no wind so no vawes, but this is where you want to be qualitywize. :)
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How to avoid black holes in sidescan? 1 year 11 months ago #10505

  • MarsArtis
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It's mounted on a kayak on a removable setup.





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How to avoid black holes in sidescan? 1 year 11 months ago #10506

  • Team Colibri
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That (probably) explains a lot. SideScan (and DownScan) depends on a stabile base, since the software renders very thin «slices» of images into the large image you see on your unit. That again has to do with the strobe-like coneangle that give these very narrow slices.

Your issue is one or two of these:
1. Your vessel is simply not stabile enough to provide the base the software in you unit needs to produce the best possible images. Waves and the motion from your padle moves the kayak sideways as well as forward, up and down, and that messes up the «stacking» of all those things slices of images on your screen.

2. Turbulence is created by your mount. Start by flipping the element around so the cable comes out backwards in stead of forwards, and test to see if it improved the images. (You can again flip the SideScan-image on your unit.) Also keep an eye on the vertical arm holding the ducer so it does not bend sligthly backwards from the waterpressure when moving, as this will lead turbulence and airbubles down the arm and under your ducer.
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How to avoid black holes in sidescan? 1 year 11 months ago #10507

  • MarsArtis
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I'll try something according to your suggestions.
Thx
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How to avoid black holes in sidescan? 1 year 11 months ago #10523

  • MarsArtis
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Was reviewing some tracks, and by activating the depth correction tool I noticed what is shown below.
It seems that during logging the sonar loose the actual bottom as soon as an high rock ends.
What settings should I check on the Elite-Ti + Totalscan to try avoid this issue?

Wrong depth

Corrected depth
Last Edit: 1 year 11 months ago by MarsArtis.
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How to avoid black holes in sidescan? 1 year 11 months ago #10524

  • MarsArtis
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Anyway, even correcting the depth I don't see the sideview fixed in those black holes that continue to be showed,.
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How to avoid black holes in sidescan? 1 year 11 months ago #10526

  • Team Colibri
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I would strongly recommend using that tool on all sonarlogs to correct bad depthreadings. With wide-angle ducers like TotalScan, HST-WSBL and 83/200/455/800-HDI you will always have a few bad readings when depths change drasticly. (Like they do when passing over those high rocks). This has no effect on your SideScan, but will improve your bathymetric map.

The best setting on your equipment for logging depth is Fishing mode deep water, 200 kHz and ping around 18 (with the depths I see in your screenshots). Using deep water mode will make the Elite fire at sligthly more power, giving a harder bottom-return. 200 kHz gives the most stabile bottom-reading and that pingspeed is more then high enough.
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How to avoid black holes in sidescan? 1 year 11 months ago #10527

  • MarsArtis
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Team Colibri wrote:
I
The best setting on your equipment for logging depth is Fishing mode deep water, 200 kHz and ping around 18 (with the depths I see in your screenshots). Using deep water mode will make the Elite fire at sligthly more power, giving a harder bottom-return. 200 kHz gives the most stabile bottom-reading and that pingspeed is more then high enough.
Considering that I'm moving with a kayak, and therefore very slowly, how would the ping speed affect the actual structure size?

Would it be better to have slower or higher ping speeds?

You seems like very aknowledged about Lowrance sonar modes.
I did try in the past to ask Lowrance customer service about an exhaustive and comprehensive explanation of the various presets of the elite-Ti serie. Their reply was not more than what is writtne in the user guide.

Do you have a clear overview of what each preset modifies?
Last Edit: 1 year 11 months ago by MarsArtis.
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How to avoid black holes in sidescan? 1 year 11 months ago #10529

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Pingspeed says something about how often the 2D-element in TotalScan fires its signal. In theory faster ping (as in more pings per second) gives more information. In real life logging, adjusting ping a notch or three does not have much effect since the actual depth is only recorded about once per 3/4-second anyway.

Scrollspeed however will have a huge effect on how structure is drawn on the screen of your sonar. With your use i’m guessing scrollspeed of 1/2 (as in one notch down from normal) would be good. The normal setting is ideal for 4-6 knots. But this does not transfer directly to Reefmaster, and only effects 2D. You can not adjust scrollspeed on SideScan or DownScan on Lowrance. Sadly I might add, as I see that lack of adjustement as the brands main downside.

As for the different modes...... That is a very good question, and I belive only a handful of Navico-engineers know the answer. I’m only answereing based on my personal experience, I don’t have first hand knowledge of the programming and algorythmes adjusted by the different modes.
Last Edit: 1 year 11 months ago by Team Colibri.
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How to avoid black holes in sidescan? 1 year 11 months ago #10539

  • iceperch
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Hello.

What is Your main propulsion? Rowing or electric motor? My expirence from rowing and mapping on inflantable boat shows that SI isn't good. Pings from 2D looks like poor shoter's target shield. Probably rowing is part of Your problem -during rowing Your kayak trim is changed.
Second option- what is Your style of mapping? I prefer drive across lake- It's allowed to grab data with similar depth for both side. Tracks must be parallel- it's help create high quality mosaics map. Best way is record each track separatley- which allow Youto comfortable editing.

I've similar Totalscan -mount like Your, but made it from steel and aluminium. It's allowed me to change angle, is very solid and stable. No air-bubble, any turbulency. Good stuff for my recognize light wehicle.
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