DFF-3D Multi-Beam Sonar

[nlol]

Watching the Furuno Making Waves - MIND-BLOWING Multibeam Sonar For Fishing video, I notice some things bothering me on my TZT3/DFF-3D installation:

a) Look closely at the triple beam screen display in the video -at about 20 minutes, 40 seconds. There is a small bump near the center on the bottom in each of the 3 beams. Something is wrong - there are not 3 perfectly spaced 'bumps' down there. There is only 1 bump and it appears in all three beam displays. Also note the symmetry of the fish echoes in the lower left corner of each beams' display. Again nope - that is NOT what's down there. Yet, my display contains the same errors; everywhere, all the time..

b) Next consider the bottoms in the triple beam image shown in the video. There is a depth gauge for each beam. Across each beam a depth change of about 10' is shown - a roughly 30' depth change across the whole scanned area. I think the images should align at the edges of the beams and the whole of the bottom image should appear as a single continuous bottom view across the 3 beams. The shown bottom contours and depths CAN'T be correct.

I was thinking I'd incorrectly connected my transducer to the DFF-3D and need to review my work. During installation I'd noticed an anomaly between my DFF-3D and the installation instruction, talked to FURUNO customer service about it, and followed their instructions. Perhaps there is an error in the instructions that at least some of us receive, or perhaps a common misunderstanding of the instructions, or perhaps you have a system problem.

nlol

 

[Jsubzero]

post screen shots of your sounder. its sounds like you may have some interference. AKA Torch Beam. show us your cross section view also.

 

[nlol]

Jsubzero: Thanks, but the boat is about 4,000 miles away - I won't be back there till end of May - so no screen shot. Besides, my screen/image looks just like the one in the video I referenced, and I found another similar image in the forums here. Perhaps I misunderstand what I should be seeing. I'm expecting 3 distinct images, each 40 degrees wide oriented as they are displayed - left to right port, down, starboard. However what I see is the same image repeated 3 times but with some variation in gain/filtering/other between the images.

 

[Basumal]

I'm guessing but I'd assume that each beam does not stop as it reaches your boat and that there is overlap between all beams. So they all detect the bump and the relative strength of the echo (given they've all got the same gain applied) is how you would locate where the bump is.

 

[nlol]

Hmmm, My explanation seems unclear, perhaps no one has yet looked at the video I referenced. But just in case, here's an analogy. Suppose you want a panoramic picture with a flash camera. That's 3 side-by-side pictures that will be stitched together to make a single wide picture. Imagine the picture is of a large group of people, too wide for the closeup you want so you take 3 pictures side-by-side. The flash goes off. The light goes out. The light bounces back. an image is captured by the camera. The camera is moved a little to capture the people beside the group just photographed ... repeat until 3 pictures and the whole group has been photographed.

The images are stitched together and viewed. A child could do the stitching with scissors - cut the 3 pictures and place them side-by-side to make a wide panoramic picture. You give 3 pictures to lil Nell to cut and tape together into one wide picture of the whole group. You look at lil Nell's work - and - opps - something isn't right. There's certainly Uncle George there, but then you notice three Uncle Georges in the picture, with Aunt Bertha right beside each time; and there's a strange offset - things just don't line up right between people, heck Bobby Jean looks like a Picasso painting, her right side is 6 inches above her left side. That's certainly not what I photographed. It looks like lil Nell had 3 copies of ONE of the pictures (each copy slightly different like the printer was running of ink); cut them; and crookedly placed them side-by-side. That is what my DFF-3D does in triple beam mode. That is what the image in the Furuno video I listed in my first post shows in triple beam mode. That is what I found in another image on this forum.

It is difficult to believe such a problem would go years without being noticed, so it seems only some DFF-3D have this problem. Could be a batch of transducers, could be in a batch of DFF-3D units , could be in some software release, could be an installation mistake made by some installers.

I expect Furuno will quickly see the problem, find the cause, and issue a fix. In the meantime, if you've not found your triple beam function to be useful, I suggest you look at your system to see if you have this problem.

 

[Basumal]

Yeah it's not the same as a camera where you have a definitive cut-off in your "image".
Anyway, I did a search on the forums and the explanation here by Snips might help you:

F

Thread 'Interpretation of triple beam image'

Mar 30, 2018

How do I interpret the multi-sounder display. In the Furuno ad's (see attached screen shot) and in actual use the images from port, center and starboard look very similar. I would have thought each view would look unique.

• flowmotion
• Replies: 3
• Forum: Fish Finders & Sonars

 

[nlol]

Basumal: Interesting - I had not seen that. OP's image seems cropped, but seems to have the same characteristic I am reporting. Thanks. If that is the way it works - the transducer elements aren't effectively angled and phased ... well, we'll see what Furuno says.

 

[sdonx]

I have wondered about the same issues.

 

[Jsubzero]

The video looks normal to me. wait for one of the moderators to respond.

 

[Johnny Electron]

@Deep Blue

 

[nlol]

'Looks normal' - really? - yes, a 'normal' image - but abnormal depiction of what is down there. Anyhow, it appears Furuno has seen my post. I look forward to their response.

 

[ToddF]

Agree it would be an improvement to have 3 separate images stiched together in a panoramic view, maybe they can improve this someday.

For now,. I've found leaving the angle at 40 but reducing the beam widths down to 20 to give me much better performance. Guessing this has to do with all the firing elements being right next to each other in 1 single transducer, as opposed to spread out over 2 or 3 transducers.

Intuitively, we all want the widest beam and sometimes it works well, like offshore, but if most of your targets are in all 3 beams, I'd narrow the beam down. Its still plenty wide and with normal boat rocking you don't miss much.

I use the triple beam mostly for fish location, not so much bottom structure. For detailing the bottom the PBG is my favorite but there's uses for History, Single Beam, and even the Cross Section.

 

[Deep Blue]

nlol,

The DFF3D features a 120° degree beam width that is utilizing 40 beams transmitted by 8 elements within transducer and each individual beam that is being transmitted is about 3° degrees. So, because this there potential for: “beam scattering”. The greater the distance between a multi-beam transducer’s elements, the longer there will be a time delay and the better separation of the echoes. The elements the DFF3D’s transducer are less than an inch and half apart, and this results for a very short time delay, with the strength of the echo returns being almost equal.

In this picture of the diver, the sounder tries to determine what the time difference when the target return that was detected on the right side of the transducer (which is stronger) -vs- then when it was detected on the left side (which is weaker). Clearly, the diver is on the starboard side of the vessel, but with the beam scattering, you also pick up echoes of the diver within the center beam, and with weaker echoes on the port beam as well.

This the only way to solve this is by having a much larger transducer with wider separated elements. However, the current demand within the Recreational Market is to making things...smaller.

 

[nlol]

That's how it works, but:
Reading the marketing literature leads me to expect MUCH better performance; leads me to think each beam is distinct- one beam each for port, down, and starboard. Instead I'm getting 3 highly compressed images, each containing the full 120 degree view. Wouldn't take much signal processing to present one 120 view showing the combined or strongest returns. Also, clearly, the speed of sound in water is a limiting factor as is boat speed, but phasing the array at trolling speeds and presenting the result as now done, would, within the physical limits, present a more informative display.

In any event, I now understand how the system works - and that mine is working properly. Thanks. I still consider the related marketing material and operating manuals to create false impressions of system performance.