Understanding the SI "dark water column"...

[rnvinc]

The SI image "dark water column" has frequently been a topic that is difficult to interpret... and even more difficult to explain....

One of the first things to understand is how the SI unit processor takes a 3 dimensional underwater world and renders it into a 2 dimensional display...
(for info understanding the SI image rendered into 3d...see... SI interpretation...in 3d - (tutorial)

Once we have a grasp on how the unit takes the "vertical dimension" water column (that resides somewhere under our boat) and lays it down flat in the SI image.... then the question arises... What exactly is this "dark water column" and what is it comprised of...??

With a lot of help and advice from some of the guys over at
Humminbird Side Imaging Forums
I hope that the following depictions will give a little better understanding of What exactly is this SI "dark water column"...??

I will refrain from a long drawn out tutorial at first.... and just post the diagrams (one for the 455kHz SI beam and one for the 800kHz SI beam)....

Then, as questions are posted, maybe we all can get a better understanding of ...

What exactly is this SI "dark water column"...??

This is the depiction for the the 455kHz SI beam...


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This is the depiction for the 800kHz beam...



Rickie

[wilbur]

Rickie, Do you have any real pics of fish or brush outside the water column? The only thing I ever found outside the column was a sunken boat.

[rnvinc]

Here's 2 shots I found in my files of scattered fish outside the dark water column...

The fish are very close to the bottom indicated by how close the fish's shadows are to the fish's echo...





And here's a Humviewer shot of a school of fish I captured that's in, over, above, around and everywhere on the screen...



Rickie

[filletfetish]

You are da man! I had no idea that the depth of water had so much to do with interpreting the SI.

[RCC]

Great pics and excellent tutorial.

Thanks

[jimp]

nice explaination again. I have been thinking that the dark water column is the depth of the water you are in as well. Rickie, your SI shots don't show the depth but your others do, so I'm thinking that the width of the dark water is also representative of the depth of water you're in.

Am I correct in this as my HDS screen shows the range in a similar fashion as your humviewer shot showing 0 to 66' out to each side, and when I look at the 2d screen on my HDS, they are very close, the dark column range is 10' while the 2d says its 10.5'.

Where you in open water when you got the shot of the suspended fish?

[wilbur]

Thanks Rickie.

[rnvinc]

nice explaination again. I have been thinking that the dark water column is the depth of the water you are in as well. Rickie, your SI shots don't show the depth but your others do, so I'm thinking that the width of the dark water is also representative of the depth of water you're in.

Am I correct in this as my HDS screen shows the range in a similar fashion as your humviewer shot showing 0 to 66' out to each side, and when I look at the 2d screen on my HDS, they are very close, the dark column range is 10' while the 2d says its 10.5'.

Where you in open water when you got the shot of the suspended fish?

I was just trolling along parallel to the bank recording a stretch of water that I could take home and study the recording on Humviewer...

I didn't even have a pole in the water so I have no idea what kind of fish they were...the individual white specks indicate they were too big for baitfish... I'm guessing they were white bass or yellow bass... I would doubt crappie would be in that large of a school...

Rickie

[rnvinc]

Jimp.. I think those shots were taken before the update came out that allowed the HB to show range lines like you see in the Humviewer and like the lines you say your HDS shows...

You are correct that the dark water column in the SI image is related to the actual water depth... I will try to explain this as soon as I get the tutorial verbiage ready to post...

Rickie

[jimp]

starting to get the hang of the SI stuff, but got to figure out the settings on the SI function to be able to see/capture some shots like you. I have been able to "see" the pilings on some docks and the resulting "shadows", but did not get any snapshots of it. Thanks for your efforts in explaining this stuff.