Topic: SI imaging cone of silence

[sonar2000]

I am hoping that my attempt at inserting pictures will work   
OK here goes.  the questinn of will side image see directly under the boat  Side imaging not the 2d down. (we know that will)  From the 1197 technical it is shown that the sonar cone is 86 degrees wide.  If in reality if that is true then we will have a 4 degree cone directly under each side that will not show any information. Hopefully we will be able to get some intensive research on this come good weather. We want to be able to construct object(s)  of height that will extend from this 4 degree cone upwards and laterly into the 86 degree cone.
now the picture are purley from the standpoint of the 86/4 degree cones really existing. and the project image is based on mathmatical representation of the cones. For this we use the Tangent of angle B math. I am not going into the math behind this because it makes my small brain hurt.   From the 3 pictures we will see that ther could exist a cone of silence (for lack of a better description). Remember this is math and not actual runs.  we will have to wait for tests to confirm.  Just something to think about this winter.   See the next 3 posts for the pictures and explanation.    Chuck

 

[sonar2000]

Ok picture 1     this show the theoritical scan of SI at 455 khz.  We are udsing the 1197 technical specs and the assumption that their data is correct.  The si wll scan 86 degrees wide and that leaves a 4 degree cone directly under the transducer

[sonar2000]

This is picture 2 ans show the cone of silence under the boat. depicted here is juist the left side transcducer. as the depth increases the cone of silence increases.  Not a lot  but in theory it does exist.  Keep in mind that if using both sides the total area of silence will be twice that which is shown here. 

[sonar2000]

Now for picture 3.  This show an object that starts on the bottom and extend upwards hopefull into the normal cone of scan.  Keep in mind that this is only a mathamatical impression of the information.  but it shows that we need to do some more testing into this.  Should make for an interesting spring.   chuck

[keizerh]

So this should double with both sides.

Maybe that's why we don't see the jerrycan overhere.

http://bbcboards.zeroforum.com/zerothread/493214-the-truth-about-down-imaging

hendrik (who quickly took his 1197 out of the boat  and put it into his bed to get warm again)

[sonar2000]

All of this is theory.  and we dont really  know how the 4 degrees is divided.  It might be 2 degrees at the top and 2 degrees on the straight down.  I just dont have any good weather to get out on the lakes right now so I am bored and looking for things to do when the weather get better.  There is a  lot of old postings here in the forum but for the new guys this might be a start to understanding the sonar and the capabilities and to research old postings.  .  I am fired up on the HB sonar and have a lot of confidence in the product.       Put your 1197 in your bed.  Hmmmmmmm Dr harry may be showing up on your door and checking you out.  I have heard of strange bed partners but the 1197 is the strangest.   LOL..  Chuck

[keizerh]

Now i'm going to bed.
I'll kick all the birds out before that

hendrik

[Whitedog]

http://bbcboards.zeroforum.com/zerothread/493214-the-truth-about-down-imaging

This is a link to a discussion on another board about the coverage of downimaging but it discusses the use of the SI information used in creating the DI.  According to this theory there is no gap in coverage below the boat and the lost four degrees are near the surface.  From my observations of objects appearing on both sides of the SI this seems to be correct.  But then I have been wrong many times in the past .

[sonar2000]

Thanks whitedog.  There has been a lot of discussion about this so thought it might be a good winter project to get ready for some spring tests.  with the 2d imaging recently provided by HB it is now posible to look at objects both from the top side and the top down.  This 2 screen advantage will probably shed some light.  If you gets some scans send me the records so I can play until we can get back on the water here.   Thanks.  Chuck

[Whitedog]

Thanks whitedog.  There has been a lot of discussion about this so thought it might be a good winter project to get ready for some spring tests.  with the 2d imaging recently provided by HB it is now posible to look at objects both from the top side and the top down.  This 2 screen advantage will probably shed some light.  If you gets some scans send me the records so I can play until we can get back on the water here.   Thanks.  Chuck

Wellll now, let me confess, I'm pretty new at this stuff too.  So far I've only had my units out about three times and have spent most of that time fishing around the stuff I've spotted using the units and not enough learning.  I have done a lot of adjusting  chart speed, ranges, sensitivity adjusting, turning filters on and off, etc..  Ont thing I have put off learning is how to record and how to do a lot of computer work with the images.  It's on my list of things to learn but spring and spawning season is about to break loose for us so despite my best intentions I suspect I will shortly spend a couple of months very shallow.  There are some great images on here and on the other forum on the link on my previous post.

I can't wait to use the Navionics chart and GPS to mark those spawning fish!!  My memory can't be trusted these days LOL.

[IRC Kevin]

After a hard weekend of paperwork my brain isn't all it should be, but does this suggest that when you pick a si target up that is sliced in half, that you aren't exactly over it, but to one side? The image below shows equally on both sides of the screen and I presumed that I was directly over it. (Im using 2 transponders and a Y cable) The target  is probably no more than 8 feet wide and lying 208 feet below the transponders.

[sonar2000]

Good post and a good question. Mostly we have been looking at the display with a single transducer.  After talking with Robert earlier the use of two transducer with the Y cable might help in directly under the boat display and especially at deeper depths.  since a lot of what we talk about is math depictions there is some questions about the actual cone of coverage.  having a left transducer and a right transducer may help some of the displays and interpretations. However remember that the center of the display to the first significant display is the water column and corresponds to the actual depth. from there the display is expanding out to farther away information. Here is a post I found that may help. 
***********Interpreting the Side Imaging View
The Side Imaging “picture” is very different than a traditional sonar view, but is easily understood with just a couple of basic tips. First, since Side Imaging looks to the sides, the position of your boat is moved to the top middle of the screen and is represented by a boat icon. Sonar returns coming from the left and right side of boat are drawn on the corresponding side of this icon. The most current sonar information appears at the top of the screen, and the older sonar history scrolls towards the bottom. Second, when the sonar ping is first emitted, it travels through the “water column” that shows up as a dark, symmetrical band down the middle of the screen. This band will show returns from fish, structure and other objects below and slightly to the sides of boat. The left and right edges of the water column vary as the depth changes - e traditional sonar, but turned 90 degrees. Lastly, once Side Imaging profiles the bottom below the boat, it continues to look further and further to the sides of the boat to define the bottom contour out to 360 feet using a topographic style shaded image. Remember, Side Imaging uses sonar, so strong sonar returns appear bright and weak sonar returns appear dark. To gain the most from this image, just apply these rules of thumb:
********
Here is what I suggest we do to help out.  Record the SI and the down image then use both screen to look at what is under the boat and what is to the side. The 1197 with the wide screen and the 997 will help in the 2 screen display and should make the under the bottom displays more meaningful.  Just some thoughts as we move forward with the DI and SI.  chuck

[metalman]

After reading this thread I got to thinking  (dangerous) about what happens with the dual SI transducer set-ups such as some guys put on pontoon boats.
I assume (again, dangerous) that in a dual set-up the only SI signals reatained are the ones that go out from each side and the "inner" signals are somehow turned off in which case there would be a "Box of Silence"  under the boat between the transducers. Even if there was no Cone of Silence because the lost 4 degrees are at the surface, wouldnt the box of Silence still be there with duals?

 Is my thinking correct??
If not can you guys explain why and I will go to my room!
I have attached a couple of rudimentary diagrams to try to help explain my thoughts.
Thanks...W

[Humminbird_Greg]

W,
You would be correct in theory.  What have seen from images posted by users though is that we have an effective Si beam that is larger than the laboratory measured 86 degrees.  So it seems that each Si bream is 90 degrees or larger as we see definite overlap in some images.  So that would mean that your “box of silence” would still exist but be shaped more like a “trapazoid of silence”, something like I marked up on your drawing below.

[metalman]

Thanks Greg, it's nice to know I'm not too far off with my thinking...W

[felvic]

W,
You would be correct in theory.  What have seen from images posted by users though is that we have an effective Si beam that is larger than the laboratory measured 86 degrees.  So it seems that each Si bream is 90 degrees or larger as we see definite overlap in some images.  So that would mean that your “box of silence” would still exist but be shaped more like a “trapazoid of silence”, something like I marked up on your drawing below.

That is to say if the cover is 90 degrees there is no dead zone anymore...true?

[Triton Mike]

The only way i could prove to myself that there is no void was to split a tree.  I actually think there is a slight overlap like Greg stated. 

TO split the tree I made 3 waypoints in SI of a tree.  I GPS the Trunk,  GPS the TOP and GPS the middle.  I lined up the 3 GPS points via the mapping screen  and split this tree right down the middle with my SI beam. 

HEre is what I got



Now one might argue that the trunk is fairly big and I wouldn't disagree with you on that.  But the limbs are split as well as indicated by the red lines connecting them.

MIke

[felvic]

As I talk on a french forum, to prove there is a overlap look at this bridge:



We are 26 m of depth, the road on the bridge is 20 m and  boat passed straight in vertical of the bridge. This bridge get three arches we do not see as the vertical is perfect and the depth moderate (therefore not enough echo).

On this picture of same bridge, where the boat thoroughly flat to the left, we can slightly see three arches as a slight echo:



Note we don't see shade of the arches as the beam does not have angle enough with the bridge.

On this bridge:



The boat thoroughly dish past to the right. We can overthink in the shade of the apron to the left. But in this depth, echo valuation more and is displayed of both sides.

In conclusion we can see when we sound deep, we should move away from the target ( aminimum of 3x beam ) , this to have one reflects more just and get true waypoints...

[sonar2000]

Felvic, you are right on the correct idea.  Top imagining is limited on depth and that is why some of the guys are building tow fish.
I wish HB would give us a beam width option on the HDSI so that with the fish we could narrow the beam...
Great pictures of what you scanned and recorded. 
This may help some understand the side image concept...
chuck