Sonar interpretation - why things look the way they do on your screen

[Larry3215]

Excellent questions and points Russ. Im off to see Logan in a few minutes, so a detailed answer will have to wait. The short version is I think we are both right - depending on the details.

Im pretty sure I do have a 2D shot of that same bait ball, but not sure how close it was taken time wise. I know I have Panoptix of the ball and your right - it looks very very different in 3D.... more later...

[Larry3215]

Larry, Just to give a quick challenge to your interpretation on the SI using DI as a control. Why would you assume that the DI would give a better representation of the bait ball's distance from the bottom? In reality that ball is 3D and who knows what it actually looks like. Both the SI and DI can Lie in different ways. Yes the SI will depict a better representation of what side the bait ball is on but 2D Sonar with a narrow cone would have a better chance of showing the bottom proximity of the bait ball.

The only thing you said that I disagree with even a tiny little bit, is that 2D will give a 'better' representation of the bait balls true depth in relation to the bottom. Actually, I dont even disagree with that really, but I would say it gives another, different, piece of the puzzle.

2D will be better in one way, but only at the point directly under the boat. With a narrow cone, it wont tell you what the bait ball is doing off to the sides. The wider cone of the downvu will also capture whats going on out further to the sides - but at the same time, exactly as you say, that wider cone can hide whats going on directly under the boat. Sideview has even wider cone angles and so captures even more of whats going on off to the sides, but at the same time can confuse and hide whats directly under the boat even more.

You are absolutely correct that side and down can both deceive in different ways, but the 2D is also deceptive and for sort of the inverse of same reason. Down and side compress a wide 3D situation down into a 2D image. Using a narrow cone on 2D, hides the wider information by taking a narrower shot thru the middle. With a wider 2D cone, you are back to the same distortions that down and side have.

You need to look at all four types of sonar (2D, down, side and Panoptix) to really know whats going on.

First, I will post the side and down pics again so they can be seen easily. I'll also add the 2D image taken close to the same time and then later some Panoptix images of that same bait ball. We actually drifted along with that bait ball for 15 or 20 minutes and I have a whle series of images showing how it moves and changes and morphs over time.





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My main point from before was that the side image was very deceptive. More so than the down image - in this particular case. The side image makes the bail ball look like its touching the bottom, The down image shows that it wasnt touching anywhere within its cone. A 2D shot taken with a narrow cone at the same time might have shown a wider gap yet - or maybe not. Like you said, it would depend on the 3D shape of the bait ball.

The next shot is a 2D image and a Panoptix image of the same bait ball taken just a few minutes earlier. The bait ball had surfaced all around the boat and the 2D image gave the impression of a smallish bait ball on the surface maybe 45 ft thick. The Panoptix shows that it varied from 20 ft thick to over 60 ft thick and extended at least 90 ft away from the boat in one direction. It was actually over 100ft x 140 ft wide at that point.





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That bail ball was moving all over the place at pretty fast clip and changing shape all the time. From 1:56PM to 2:15PM it went from 80-100 ft deep, up to the surface all around our boat, then back down to 100-175 ft deep, then back up to 75-125 ft deep. During that same time it changed shape and varied from well over 100 ft long by 140 ft wide by 100 ft thick down to a much tighter 40x40ft ball. It was being harassed by salmon, seals and diving birds which made for some good action on the screen.

This next Panoptix image gives a good idea of how complex something like this can be - details you will never see on any sonar other than Panotix.



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This last image was taken just 2 minutes after the side and down images and the bait ball had moved a good bit, so it cant really be compared to the other shot directly.

[Larry3215]

None of the Panoptix transducers have the same dead zone issues traditional transducers have. Dips in the bottom and slopes wont give them any problems as long as the beams can see and hit the fish.

I can imagine a few possible exceptions to that, but it would only be in unusual situations.

Fish can still hide and wont be seen, but for the most part, only if they are behind something or buried in brush, weeds, etc. No sonar can see behind walls, humps etc or into thick brush or weeds.

I need to re-visit this. Ive been thinking about it some more and I was wrong. I wasnt picturing how slopes would effect Panoptix correctly. The cones or beams of a Panoptix are very different from other sonars. Paonptix can have some very large dead zones on slopes - in some cases they could be very large.

I want to wait to go over this in detail after I get into Panoptix cones/beams and how they are different. I really need to get out on the water and get some screen shots in real world situations in order to explain it properly.

Without going into the whys, the short version is as follows for forward and down Panoptix.

Forward Panoptic - PS31, 21 - will have dead zones when looking parallel to slopes and wont have then when looking up or down a slope. In other words, if you point the beam up or down a slope you will be fine. If you point the beam along the side of a slope, there will be dead zones. This has nothing to do with which way the boat is moving or pointing. Its all about which way the beam is pointing. If you set the PS31 to the narrowest cone angle, it will have a much smaller dead zone.

The PS30 will tend to be just the opposite, but its more complex because of the way the beam can be steered and its huge cone angles. For the most part, the PS30 should have smaller dead zones when you are driving parallel to a slope and worse when going up or down slope. This is just the opposite of forward view and to some degree, 2D and downview. Its complicated by the fact you can steer the beam fore and aft and vary the cone widths so much.

[mosin]

So..Larry sir, from what I understand is that you are saying that SI beam is just a (somewhat complicated) pulse, aimed to the sides, instead of what people might commonly mistook as a scanning beam. Basically, similar to a 2D sonar reading over a slope (albeit with higher freq & diff fan shape), which produces those thick bottom picture on the screen. I guess in SI that thick bottom is replaced with a more detailed color gradations. Is my assumption correct?

[Larry3215]

Thats pretty much exactly it. The side "scan" beams dont scan side to side - which is how most people think of it and how the marketing makes it sound.

Its just as you say - they work just like 2D except for being tilted to the sides and much narrower cone angles front to back and the higher frequencies. The narrow cone angles and higher frequencies allow for much finer detail and resolution in the screen images. Basically, the bottom thickness you would see on a slope in 2D is the bottom you see on sidescan - but much enhanced. Downview is more like 2D in that both sides are over lapped. Its mainly the narrow front to back cone angles though that make for better images.

The other big difference is the color palate and contrast level on side/down make it easier to see slight variations in the return signal strength - which shows the bottom structure much better than 2D ever could..

[LWINCHESTER2]

it seemd that those quadrabeam / humminbird 47 got some correct ideas back then. are there any consumer multibeam SI tranducers being produced?

I used Matrix 47 for years. The xd had 6 elements, 3 for the left and 3 for the right. There was a view that could be selected to show each beam separately so that you had some idea how far to the left or right the fish were. I also acquired an engineering code I could enter that would stretch that to 11 columns. 11 columns were possible because the unit could show what exclusively showed up in each cone and then add columns in between for returns that showed up in adjacent columns as a separate column. The problem it had was that all the elements used the same frequency and so the pinging had to rotate through them. That made it a little slow. All these have been discontinued and now since Panoptix has hit the scene it is certainly obsolete. However, at one time, I thought it was the best thing going. Sorry Larry. Off topic.

[Larry3215]

Not off topic at all as far as Im concerned. That was some interesting info I didnt know. Thanks for filling that in.

[gohoos2011]

I'm assuming med chirp and 83 kHz are similar in cone angle and same with high chirp and 200khz? Is there a better time to use chirp over traditional 2d or just use chirp all the time

[Larry3215]

You need to look at the specific specs for the transducer. They are not all the same. There are Hi-Wide transducers that have wide cone angles at hi frequencies.

In general though, when you use CHIRP you are getting all the cone angles at the same time over what ever the frequency range is set to. CHIRP sweeps through the frequencies on each pulse - which also means it is changing cone angles at the same time.

[Larry3215]

Im sorry guys. Im too pissed off at Garmin to finish this off.

http://www.bbcboards.net/showthread.php?t=797744


If you are interested, I have most of the same info, including a lot more on sidescan, on this thread:

http://www.northwestfishingreports.c...p?f=20&t=23810

[RangerRic]

Here is another possible situation where the wide cone hides stuff that the narrow cone can show. With the wide cone, you dont even know the hole is there and never see the fish. The narrow cone can show both - if you happen to drive right over the top of it.

Larry: Might this be how the Lowrance video 'lost' the culvert for the Garmin display (i.e. using a lower frequency/larger cone angle than the Lowrance unit used) ?

[Schins]

Quadrabeam was a bit of an odd ball. It wasnt the same "multibeam" I have been talking about.

Lots of sonar brands have had what they called "multibeam" sonar setups. I guess you could break it down into two basic types.

One type is any sonar transducer/mfd that has more than one beam. Pretty much any transducer that does more than one frequency at a time or that has sideview is 'mulibeam' by that definition. That just means it has more than one beam. But they dont interact with each other except for maybe being shown in a combo screen or possibly even a chirp setup.

The other main type for sport fishermen, are phased array sonar units with multiple, narrow, electronically steerable beams. Panoptix and the new Furuno equivalent thats just getting released, are two examples of that type of multibeam. Simrad also has had a forward looking setup thats more for seeing bottom ahead of the boat but works basically the same way. There are also commercial variations that cost in the $100k range that are in this category.

Garmin bought a company called Interphase a while back and thats where Panoptix comes from. They patented one type of phased array multibeam sonar that Garmin then developed into Panoptix. I have no real clue how they did it, but Panoptix is light years ahead of what Interphase had.

Quadrabeam was multi-beam only in so far as it had 4 beams. It was really a split frequency 2D sonar with added side lobes that were very crude side scan beams. The two center beams were I think 83 and 200 khz. Just their normal 2D sonar but with both running at the same time. One wide cone and one narrow cone. The side lobes were 455 khz(?) but they were not narrow front to back beams. They were very wide front to back which made them more like 2D than sidescan as far as image quality and detail.

You can get a "quadrabeam" type display - with much better quality on the sidescan part - on any modern mfd, by spliting the screen with sideview on the bottom and chirp 2D on top.

Traditional sidescan and the the Panoptix type multibeam are not even close to the same thing.

As far as a mutibeam sidescan - there are at least two or three different 'multibeam' technologies being used on the hi-end oceanographic type equipment - like the stuff NOAA uses for example. I havent kept up with that stuff but IIRC one of them uses some sort of back scatter technology in addition to or along with phased arrays. Its been several years since I read up on that stuff, so Im way out of date Im sure.

I remembered those old Interphase's and actually tracked one down last year to see how it would do.

The resolution of the unit is too low to be much good.

[Bass newb]

excellent tutorial. Thanks and keep it coming. I have made it my mission to learn how to use this stuff this season. I'm bound and determined to catch me some deep fish this year!

[Schins]

I used Matrix 47 for years. The xd had 6 elements, 3 for the left and 3 for the right. There was a view that could be selected to show each beam separately so that you had some idea how far to the left or right the fish were. I also acquired an engineering code I could enter that would stretch that to 11 columns. 11 columns were possible because the unit could show what exclusively showed up in each cone and then add columns in between for returns that showed up in adjacent columns as a separate column. The problem it had was that all the elements used the same frequency and so the pinging had to rotate through them. That made it a little slow. All these have been discontinued and now since Panoptix has hit the scene it is certainly obsolete. However, at one time, I thought it was the best thing going. Sorry Larry. Off topic.

sounds like Humminbird needs to get on the modern version of that asap

of course, its still historic-type graphing instead of live

[Schins]

Regarding the Quadrabeam.....it was still being used in Humminbird's bargain-basement model (185 iirc?) but only utilized 3 beams.....one center, and one to each side. Unfortunately since it was tied to a lowly head unit it was quite restricted.

As a fishfinder it would show fish off to each side as turned to the left or right.....left-facing fish were in the left beam, right-facing in right beam. And darker, iirc, was in the narrower center cone.

But it needed to be tied to a better head unit, as the practice of it was weak compared to the theory. I tried jigging with it one time and it didnt show a thing.

[Wayne P.]

Regarding the Quadrabeam.....it was still being used in Humminbird's bargain-basement model (185 iirc?) but only utilized 3 beams.....one center, and one to each side. Unfortunately since it was tied to a lowly head unit it was quite restricted.

As a fishfinder it would show fish off to each side as turned to the left or right.....left-facing fish were in the left beam, right-facing in right beam. And darker, iirc, was in the narrower center cone.

But it needed to be tied to a better head unit, as the practice of it was weak compared to the theory. I tried jigging with it one time and it didnt show a thing.

The Quad Beam transducer was an accessory for the Side Imaging units until it was discontinued. The 798ci SI Combo I used to have and the two 1198's I still have has that setting in the Connected Transducer menu.

Yes the 2D is 83/200 kHz and the side beams are 455 kHz.

There are three ways to display the side beams, horizontally, vertically, and slanted.

[Schins]

Wayne, wouldn't it have made sense that the Helix 5 sonar-only model use the quadrabeam as standard equipment? It would have a fish-finding edge over other brand's sonar-only models.

Why take a step back in tech when it's already there?

[Wayne P.]

Wayne, wouldn't it have made sense that the Helix 5 sonar-only model use the quadrabeam as standard equipment? It would have a fish-finding edge over other brand's sonar-only models.

Why take a step back in tech when it's already there?

Must not have been a popular sonar function after Side Imaging came out. Still would have to produce a unit and transducer with the same number of sonar crystals as a Side Imaging unit (left, right, and 2D).

[Larry3215]

Larry: Might this be how the Lowrance video 'lost' the culvert for the Garmin display (i.e. using a lower frequency/larger cone angle than the Lowrance unit used) ?

Sorry! I missed this somehow.

No, whats going on in the Lowrance video is very different.

Thats a situation where the CV transducers "Clearvu" sonar signal just isnt strong enough to pick up details right under the boat as well as a transducer that actually has a downvu element.

The CV transducers have no down element, so they have to use the down pointing portions of the two sidescan elements to see straight down. The sidescan elements are pointed to the side, so anything directly under the boat is always going to be in a weaker part of the beam, and possibly even in a null zone where there is no signal at all. CV transducers are never going to perform downvu as well as a transducer that actually has an element that looks straight down.

[CATFISHUNTIN]

LARRY3215..I just want to add my thnx. i have watched almost every YOUTUBE video on this but they do not compare to the fountain of knowledge you have/are providing. I just purchased the GARMIN 93SV and am looking forward to 2018 fishing and will probably print this thread as a Reference Guide.. Again much Thanx