Author Topic: Humminbird Advanced Sonar - : DI Coverage Area  (Read 22762 times)

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Offline Fishton

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Humminbird Advanced Sonar - : DI Coverage Area
« on: June 07, 2011, 10:36:10 PM »
For all you Humminbird sonar gurus out there:-

If you were in 60 ft of water, and 2 bass swam past 10ft to either side of the transducer just below the surface - Would you see them on Down Imaging (798, 898, 997, 998, 1197 & 1198) if the DownImaging Coverage was set to NARROW?



And what would happen if we were in water 120ft deep.  Would the coverage area to either side of the transducer now be 40ft just below the surface!



« Last Edit: June 10, 2011, 10:05:02 PM by Fishton »


Offline Fishton

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Offline stillbear

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #2 on: June 10, 2011, 05:46:07 AM »
Thanks for the info.   Gary

Offline SonarTRX

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #3 on: June 10, 2011, 10:02:16 AM »
Hi Fishton,

Your original post had the following statement (see quote below) that was accompanied by an illustration that is no longer shown in your post after you edited it out.

Quote
What this means is that when the DI mode is set to wide, it is using the FULL left and right views to create 'Down Imaging'.  But when it is set on narrow mode, it is ONLY using the part that overlaps beneath the boat.


I am glad you also realized that it was wrong, because that particular statement was exactly what made me respond to your post with this:
(---end edit.)


If what you say is right (i.e. "..when it is set on narrow mode, it is ONLY using the part that overlaps beneath the boat") , how does the sonar processor know what part of the beam (left/right side-scan) is overlapping when set to the "narrow mode"?

Option1:
Are the left and right side pings "staggered" in time, so the right-side transducer (receiving) signal can be processed based on the left side's ping (and the left-side based on the right side pings), for true knowledge of what comes back from the opposite sound source?

Option2:
Is the left and right side signal encoded so the the processing algorithm can separate out the two signals?

Option3:
Is it looking at it purely by time, by ignoring any signal that arrive later than the bottom-return? (i.e. a wedge-shaped half-circle domain), and then perhaps matching detected signal patterns from the two channels, assuming that if a pattern shows up on both channels, it must be in the overlapping region?

Option4:
...?


Best Regards,
Tore

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« Last Edit: June 12, 2011, 03:29:26 AM by SonarTRX »

Offline Fishton

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #4 on: June 10, 2011, 08:50:24 PM »
Hi Tore,

I am making no statements, just asking questions from my peers that have more experience than myself.

So what is the answer to my question? 

"If you were in 60 ft of water, and 2 bass swam past 10ft to either side of the transducer just below the surface?" (narrow mode)

Offline SonarTRX

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #5 on: June 10, 2011, 09:33:15 PM »
Hi Fishton,

Well, you made the statement (in bold) that the sonar "...is ONLY using the part that overlaps beneath the boat". Where did that information come from? Is it your interpretation, or does it come from official sources?

Tore

Offline Fishton

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #6 on: June 10, 2011, 10:02:06 PM »
Overlaps is the wrong word for sure.  But according to OFFICIAL SOURCES (bold & caps) Down Imaging on narrow mode is supposed to represent an area equivalent to 20 degrees directly below the transducer. (1/3 of depth coverage area side to side)

BUT, more importantly Tore - lets look at the MAIN question that I am asking here.

Will you see the two fish as shown in these two images?

Offline SonarTRX

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #7 on: June 10, 2011, 11:45:51 PM »
Hi Fishton,

I noticed you edited your original post and removed an illustration, so I guess I should take that as a sign that you got my point. :-)

I think the answer to your main question is (should be) NO, unless the description of Down Imaging in "Narrow Mode" is wrong. Then again, marketing information always seems to be rather simplistic, so I would not be surprised if the fish shows up. And if it does show up, it would probably be at the wrong depth (i.e. at a depth equal the horizontal range to the fish).

I guess someone needs to make up a couple of "fake fish" and do some testing!

Tore

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Offline Fishton

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #8 on: June 10, 2011, 11:58:57 PM »
I removed it because you were getting distracted from the REAL question.  ;D

Ok, it seems everybody is battling with this one.

1. Do you own one of the following 797/798/898/997/998/1197 or 1198?  (these are DI from SI units - in other words, they do not have a directly down looking 455/800 'crystal' - only a left and right)

2. Have you ever played around and understood the difference between the DI settings - wide and narrow?

Offline Rickard

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #9 on: June 11, 2011, 11:43:50 AM »
Hi Fishton,

I have a 981 model that also can do DI from SI, but I never use it because this mode doesn't say more than the SI views do. Actually, I think DI is just a confusing mix between the SI views and a dedicated DI crystal has no theoretical potential to do it significantly better.

But I still want to bet on your question, yes I think the fish will appear on the display in both DI from SI modes. The reason is as simple as the technology I think they use. Wide mode means that returns which arrive late after the arrival of the first bottom return are displayed, narrow mode means this time is reduced. If a flat seafloor is assumed, this will result in display of a part of the seafloor that is 20 degrees wide. Anything that is located in front of a SI crystal and closer than the max time frame, and has the ability to reflect sound effectively will appear in the narrow DI from SI image.

Next bet, please  :)

Rickard

Offline Fishton

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #10 on: June 11, 2011, 09:16:35 PM »
Hi Rickard,

I think DI is just a confusing mix between the SI views and a dedicated DI crystal has no theoretical potential to do it significantly better.  - The first part of this I agree with 100%.  As for the latter, what do you mean by "it"?

So the way you understand DI from SI, is that if DI is set to narrow mode, then one would see fish on the surface at a distance from the transducer equal to the depth?

So if you were in 60ft of water, you would see fish 60ft to your right, and 60ft to your left? 

Offline Rickard

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #11 on: June 12, 2011, 01:21:23 AM »
Fishton,

With 'it' I meant DI.

Yes, in a DI from SI system one would see fish near the surface at a distance from the transducer that is equal to the depth. Of course, the received echo must be strong enough, but sound is transmitted parallel to the surface so there is a chance the fish will be seen.

A system with a dedicated DI transducer won't show that fish because the sound window in the DI crystal is parallel to the seafloor. In theory, sound is transmitted by a DI transducer parallel to the surface, but this doesn't happen in a practical transducer.

You can arrange with your own dedicated DI by rotating an SI transducer until one of the SI crystals points towards the seafloor. If range is set to something just beyond the depth, the result will be a DI view.

Conversely, a single-sided SI system can be arranged with a DI transducer if the transducer is rotated about 60 degrees and directed to one side.

Regards,
Rickard

Offline Fishton

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #12 on: June 12, 2011, 09:45:45 AM »


So what you are saying is that this fish just below the surface would look like this on your DownImaging view, even when set to 'Narrow'?


Offline Rickard

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #13 on: June 12, 2011, 03:51:14 PM »
Exactly,

that's what I mean. I think the terms 'narrow' and 'wide' can be misleading. They are appropriate only when they refer to the width of the seafloor that is displayed.

/Rickard

Offline Fishton

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #14 on: June 12, 2011, 09:35:51 PM »


So in a case like this, where 2 fish just below the surface and nearly ONE HUNDRED  feet APART would appear to be sitting right next to each other directly beneath the boat?


Offline Rickard

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #15 on: June 12, 2011, 11:24:05 PM »
Yes,

this can happen. The system can't know from where an echo comes, it can only tell the distance (from time) and the energy level in the echo. In a DI from SI system the system can discriminate between left and right from the beginning, but that info is not (cannot be) presented in the DI view.

/Rickard


Offline Fishton

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #16 on: June 13, 2011, 01:12:46 AM »
Can you imagine the disappointment of an angler, who does not totally grasp the practical implication of DI from SI, and has been jigging below his boat for the last hour or two after seeing these two fish 'holding on structure directly beneath the boat' without any success?   When in fact these fish were nearly 100ft apart just below the surface on either side of the boat, and should have been targeted with a surface popper!!

Offline Rickard

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #17 on: June 13, 2011, 01:43:06 AM »
Yes, of course the angler would be terribly frustrated. But I don't think this situation is common because only a large fish can reflect enough with energy from that position. Sound transmitted parallel to the surface is much weaker than sound that is transmitted at an angle towards the seafloor. I think the risk for this source for confusion is less with a dedicated DI transducer, but the risk is just reduced, not completely eliminated.

One must remember that the SI and DI views are not so good at displaying fish anyway. In most situations a fish appears like a small dot because of the narrow beam. SI and DI are fantastic tools for analyzing the conditions, finding spots where fish can appear and so forth, but detection of fish is done much better with the conventional and wide downward looking beams, I think.

Rickard

Offline Fishton

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #18 on: June 13, 2011, 02:09:50 AM »
I agree with your statement - "because this mode doesn't say more than the SI views do. Actually, I think DI* is just a confusing mix between the SI views"  * DI from SI technology.

True DI, such as that in the 570, 597 & 788 HD DI, with a dedicated down looking high frequency crystal is a phenomenal fish finding and structure detailing tool in my opinion, when fishing depths from 10 - 180ft.

Offline Rickard

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #19 on: June 15, 2011, 02:38:50 PM »
I started to ponder about the beam forms of "true DI" and "DI from SI" and made some graphs. When comparing the graphs it seems as the difference between energy levels parallel to the surface is larger than I thought.

The first image shows the theoretical beam forms in a dedicated DI crystal. The simulation is based on the -10 dB beamwidths in the specifications for the 596c HD DI model. The black curve shows the beam form at 455 kHz and the 800 kHz beam is red (for some reason it's difficult to see the difference between colors). The -10 dB limits are shown with straight black and red lines for 455 and 800 kHz, respectively. At 455 kHz the energy level close the surface is about 18 dB below the level in the vertical direction. Thus, a fish close the surface will be hard to see.

Second image shows the beam form of the right SI beam in a HDSI transducer. The left beam is omitted. At 455 kHz a fish close the surface will be hit by a higher energy level than a fish beneath the transducer, if both fish are located at the same distance from the transducer.

Since left and right SI beams overlap there is probably also some interference between the beams because the crystals are mounted far apart. The expected interference is not shown in the graph. This kind of interference is sometimes visible in normal sidescanning and they show like stripes on the seafloor close the water column. This will reduce the quality also in a DI from SI view. I haven't tried it myself yet, but I believe the interference can be reduced by physically stopping the sound with a wall that extends from under the SI crystal and one or two inches downwards.

All this means there are rather strong theoretical arguments in favour of a dedicated DI transducer.

Rickard

ila_renderedila_rendered

Offline Fishton

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #20 on: June 15, 2011, 07:12:57 PM »
This is really valuable information Rickard, and pretty much 'seals the deal' from a technical perspective. 

The only thing I can't seem to understand fully is how is the soundwave / echo 'manipulated' in the three DI settings (Wide', 'Medium' and 'Narrow').

Offline SonarTRX

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #21 on: June 15, 2011, 10:09:23 PM »
Rickard,

Dont you think saying that "there are rather strong theoretical arguments in favour of a dedicated DI transducer" will depend on what fish you are looking for?

1. First of all, everyone needs to agree on the meaning of the "down" in "Down Imaging" (DI). It seems like everything in the water should be considered "down", since it is truly below the surface ...unless your boat is on its way to the bottom :-).

2. Nowhere in my manual do they say that the vertical axis of the DI view is the depth. In fact, the illustration used to explain the Down Imaging View (see attached image) has two numbered items (8 and 9) saying "Upper range" and "Lower range" indicating that the Y-axis is the RANGE, not neccesarily the vertical distance below the transducer (i.e. depth). 99% of the confusion discussed in this thread is probably because it is not clearly labelled "range" in big bold letters on that view).

3. Based on Rickard's beam forms, it seems obvious that the "DI from SI" mode will be able to pick up more of the fish located higher in the water column, to each side of the boat. Sure, it is hard to know what side the feature is from, but that would also be true with the DI view from a "True DI" configuration. Again, the operator should think about the vertical DI axis as the range from the transducer, not depth.

4. The dedicated DI transducer configuration (or "True DI" as Fishton calls it) will pick up more fish from deeper water, but the cone-shaped beam form will cover volumes ahead and behind the boat, so it may look like there is more fish directly below the boat than there really is. The same fish keeps showing up in the vertical scan-line in the DI view for a long time, even though it may be quite a distance behind (or ahead, or to the side of) the boat.

Perhaps by simply rewriting the description of the Down Imaging View, it would be easier for people to grasp what they see on the screen.

- The vertical axis should be clearly labelled "RANGE".
- Instead of saying that the DI View displays "the down beam portion" of the data from the Side Imaging Beams, they should clearly state that it is based on range, not depth (if that is the case).


Tore
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Offline Rickard

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #22 on: June 16, 2011, 08:03:36 AM »
Fishton,

Thanks, it took some time making the graphs... I think they use time to set the width of the DI view. The alternatives would be switching between several DI crystals with different widths or physical shadowing of the beam, neither of these methods is realistic, though (they are possible but expensive and clumsy).


Tore,

Of course the appropriateness of DI will depend on where we want to search for fish. If we search for shallow fish we need a beam parallel to the surface and no vertical beam, if we search for fish close the seafloor a vertical beam is needed without any disturbance from objects far to the side and close the surface. With "DI from SI" all fish is displayed and with "True DI" all but some fish high up in the water column is displayed. So none of the DI principles is really perfect for any of those purposes.

If you ask 1000 fishermen about how they interpret the DI view I bet 999 of them say it shows the bottom profile and fish in a narrow sector between the boat and the bottom. If they try to catch a fish that is shown close the seafloor they will place the bait close the seafloor without any other thoughts. A user friendly fishing system should be adapted to the user's spontaneous interpretation of the view and I don't think the concepts in the manual or on the scale has any effect on their interpretations. I feel a new invention in sonar technology is needed here...

The dedicated DI transducer has a 2D 455 kHz mode, but that view is displayed separate from the DI view, if I have understood it correctly, so there is no cone-shaped portion involved in the dedicated DI view. This new 2D 455 kHz beam (and the conventional 200 kHz beam) can be used together with the DI view to decide if a fish is located close the seafloor or not. If it's close the seafloor the fish should appear in the 2D and DI views, if the fish appears only in the DI view it must be located to one side (not possible to know which side) and high.

Rickard


« Last Edit: June 16, 2011, 08:05:29 AM by Rickard »

Offline Rickard

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Stripes with SI and DI
« Reply #23 on: June 17, 2011, 03:50:57 PM »
A made a new simulation that shows the interference in the overlap section between the right and left SI beams at 455 kHz in an SI transducer. Lengths of the "fingers" can vary alot depending on the precise positions of the SI crystals. "Fingers" like these do not occur with a single crystal dedicated DI transducer.
ila_rendered


The HumViewer snapshot below is an example on how the "fingers" cause stripes in the image. The right window shows the SI view and the left shows the DI view. The stripes are clearly visible in both views. I used 262 kHz in a doubleducer with two 262/455 kHz SI transducers. The stripes are visible also at 455 kHz, but the affected sector is narrower.

Rickard
ila_rendered
« Last Edit: June 17, 2011, 04:04:23 PM by Rickard »

Offline Fishton

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #24 on: June 17, 2011, 08:29:40 PM »
Rickard,

 On my very first time out with version 4.7 'Now with DownImaging' I remember being very disappointed, and remember saying that the object appeared to be clearer when it was slightly off to the left or right of the transducer when I passed over it. 

Here is an image that was part of a huge debate last year January when DownImaging was announced.  Take note of "Directly beneath boat" part.



Your diagrams, images and excellent explanation of these sound wave properties has been a tremendous help.  I hope you don't mind if I use this material in my sonar courses when I explain the difference between 'DI from SI' as Humminbird calls it, and 'True DI' as I call it.

John Easton
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Offline Rickard

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #25 on: June 18, 2011, 12:32:09 AM »
Fishton,

By all means, if you trust my diagrams, you may use them. But please, be aware these are theoretical curves, in a practical transducer things use to be more blurred. As an example, the interference "fingers" are not as conspicuous on the display as one expects when looking at the theoretical curve, but they exist.

Regards,
Rickard

Offline Fishton

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #26 on: June 18, 2011, 09:53:38 PM »
Fishton,

By all means, if you trust my diagrams, you may use them. But please, be aware these are theoretical curves, in a practical transducer things use to be more blurred. As an example, the interference "fingers" are not as conspicuous on the display as one expects when looking at the theoretical curve, but they exist.

Regards,
Rickard

Thank you Rickard.

And sure, they might be 'theoretical curves' but still important that a SI user is aware of this 'phenomenon'.  I call it 'blind spots' in my classes.

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #27 on: June 20, 2011, 06:33:51 AM »
Rickard,
Have you ever checked to see if these “fingers” are in the newer XHS-9-HDSi-180-T transducers?

Greg Walters at Humminbird
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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #28 on: June 20, 2011, 02:52:13 PM »
Greg,

Yes, I have checked with the HDSI transducer, and the "fingers" are sometimes visible at 455 kHz, but that's rare, really. Unfortunately, I can't test at 800 kHz with my old 981 model. It's not common to see the fingers at 455 kHz in the old SI transducer either. In simulations I can see that the fingers become shorter the higher the frequency, and at 800 kHz they are about 20 dB below max level. The number of fingers increases with frequency making the stripes thinner and harder to see.

Rickard

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #29 on: June 24, 2011, 09:58:07 AM »
This subject is perhaps old and boring, but I thought I should show some ultimate simulation results on the "old" SI transducer. Since I have carved out the SI crystals in this transducer I know the exact dimensions of the crystals (5 x 6 mm). I hesitate to show simulations of the newer HDSI transducer because I don't know the dimensions and the specifications on beamwidths in the manuals are inconsistent. Note, that sound is sent towards the surface, that's why you sometimes see waves in the images. That's also a reason why the transducer should be mounted as close the surface as possible. As a late response to the debate on coverage of downimaging I show the overlap between the SI channels, it's 60 degrees. Thus, an object beneath the boat has no chance escaping detection if a SI transducer is used.

There is one more "finger" in this solution because I used a better estimate of the inter-crystal distance. This distance is set to 65 mm. The sound window is 6 mm.

In general, the most critical parameters are frequency and width of sound window. There are catastrophic combinations when the first nulls in left and right SI beams coinside which (in theory)causes a narrow silent sector beneath the boat. The old SI transducer that is simulated here is not close a catastrophe.

Rickard

Beam form at 262 kHz in the SI transducer.
ila_rendered

Beam form at 455 kHz in the SI transducer.
ila_rendered
« Last Edit: June 24, 2011, 02:43:08 PM by Rickard »

Offline Fishton

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #30 on: June 24, 2011, 08:47:53 PM »
Hi Rickard,

Old and boring?  Hardly. ;D

Why?  - The difference between 'DI from SI' and 'True DI' is one of the most misunderstood aspects of high frequency sonar.

There are situations where SI from DI can produce exceptional images of cover (big laydowns - see image below.  I have put this tree into perspective just in case someone mistakes it for a little brushpile) as well as large shoals of fish, as we have seen many times before.  Which proves your statement - Rickard "Thus, an object beneath the boat has no chance escaping detection if a SI transducer is used."



But I am not out there to just take great screenshots, I am there to FIND FISH.  And knowing their EXACT POSITION in relation to the boat is absolutely CRITICAL.  So if two fish nearly 100ft apart that are just a few feet below the surface, APPEAR to be sitting on some cover 'DIRECTLY BENEATH' my boat ... How do I tell the difference when deciding between a surface popper or a jig?  * see post #14 in this thread.

DOWNIMAGING FROM SIDEIMAGING:


TRUE DOWNIMAGING:
« Last Edit: June 24, 2011, 10:36:29 PM by Fishton »

Offline Rickard

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #31 on: June 25, 2011, 02:56:04 AM »
Ok, this subject seems interesting after all  ;). I'm afraid there's no way to tell from a DI view if you should use a surface popper or a jig when the fish is displayed just above the seafloor. This goes for DI from SI and "True DI". The situation is better in True DI because the beam is rather weak sideways, but the risk for confusion still exists.

I think one can determine the position of the fish, to some extent, by combining views:
DI FROM SI: If the fish appear in both left AND right SI view it's likely close the seafloor and somewhere beneath the boat. If the fish appear in only one SI view you know the direction to the fish, but not the depth of the fish. Actually, this strategy makes the DI view unnecessary.

TRUE DI: There is no way to tell wether the fish is to the right or to the left by analyzing some of the other views. One can tell if the fish is beneath the boat or not by inspecting the new 2D 455 kHz view. If the fish appear (you must assume it's the same fish....) in the DI AND the 2D 455 kHz views one knows the fish is under the boat and also the depth to the fish. If the fish only appear in the DI view it's somewhere else at unknown depth.

These strategies are not foolproof and rather tiring to use, though.

It's obvious in your images that the DI results in the HDSI transducer are bad in comparison to the dedicated "True DI". I think this has to do with the fact that the HDSI transducer was not designed for DI from the beginning. It's probably possible to find better combinations of frequency and inter-crystal distances which provide better DI from SI images than the present HDSI transducer.

Rickard

Offline Fishton

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #32 on: June 25, 2011, 10:54:47 AM »
As a 'daily user' of the various technologies and brands, I get to see the benefits and weaknesses first hand.


Offline Rickard

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #33 on: June 26, 2011, 01:22:10 PM »
Fishton.

You make us jealous with your equipment! I can see you have top models from HB and Lowrance... It's very tempting, but perhaps inappropriate to ask in this forum, which one do you prefer? I guess the answer begins with; It depends..? I understand if you refrain from answering.

Regards,
Rickard

Offline Fishton

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #34 on: June 26, 2011, 08:37:14 PM »
Rickard,

"It depends .."  is spot on.  The best advice I could ever give an angler that wants the best performance in all aspects of sonar / fishfinding, is - Having a Humminbird AND a Lowrance is NOT illegal. 

Offline sonar2000

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #35 on: July 01, 2011, 08:54:53 AM »
As I have said many time before......Each sonar has strong points and each has its limitations.
Certainly cost has a strong influence on the product but even the costly units have limits.
Which is why from time to time you see boats like this one with a bunch of products.
In search and recovery we use different products depending on the geographics, area need to search, time since last sceen, surface scan, or side scan, sector scan or forward looking.It all depends on your budget and needs.
One thing is important.  Learn that which you have and be good within that product. Knowing when to use and when to call for additional assistance makes the difference.
Chuck   (a.k.a. the ladder man)
« Last Edit: October 20, 2011, 06:17:46 AM by sonar2000 »

Offline Moose1am

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #36 on: October 20, 2011, 02:40:14 AM »
For all you Humminbird sonar gurus out there:-

If you were in 60 ft of water, and 2 bass swam past 10ft to either side of the transducer just below the surface - Would you see them on Down Imaging (798, 898, 997, 998, 1197 & 1198) if the DownImaging Coverage was set to NARROW?



And what would happen if we were in water 120ft deep.  Would the coverage area to either side of the transducer now be 40ft just below the surface!






Not sure yet.  I thought you were asking about regular sonar beams but you are asking about DI formed from the SI Beams.  Going to read this thread now..
« Last Edit: October 20, 2011, 02:42:41 AM by Moose1am »
Regards,

Moose1am

Offline sonar2000

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Re: Humminbird Advanced Sonar - : DI Coverage Area
« Reply #37 on: October 20, 2011, 10:47:16 AM »
Down imaging is a cone pointing down. Thus as it gets deeper it gets wider at the bottom......which of course means it is narrow at the top.
I can remember turning the transducer 90 degrees sideways to look under docks and back in rock overhangs.  Life was not the science it is today..
This was an issue for SAR in the early days as shallow depths made targets very hard to identify. And still is today....
You get just a slice of the target.  Color addition helped a lot with hardness/softness so the little blip was easier to detect...
Thankfully side scan and side image relieve this issue.
Chuck
 


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