Interpretation of triple beam image

flowmotion

Furuno Fan
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.
 

Attachments

  • triple beam.JPG
    triple beam.JPG
    108.9 KB · Views: 1,066
Flowmotion,
You raise a fair question, how come all three beams aren't totally unique? Without getting to deep into multi-beam theory I think it comes down to the two main components i.e timing and returned target strength. Timing of the return is the first part, if a target is off to the port side the return comes back to the left side of the transducer first. But it just doesn't stop there it continues on to the transducers right side and beyond. Now the sounder tries to determine the time difference between when the target return was detected on the left side of the transducer vs when it was detected on the right side. It also is comparing the strength of the return. The greater the distance between a transducers elements the longer the time delay. In high end survey multi-beams the receiver array can be four to eight feet across, the elements the DFF3D transducer are less than an inch apart. The results is a very short time delay and the strength of the returns being almost equal.

Also a lot has to do width and angles that the beams are set at. Below is a pretty nice example of a few predator's working a small bait school off to the port side.


Snips
 

Attachments

  • TZ 4.JPG
    TZ 4.JPG
    42.8 KB · Views: 1,048
  • TZ 2.JPG
    TZ 2.JPG
    96.8 KB · Views: 1,048
Great explanation.

Does the overlap effect increase with depth as the delay between the left and right detectors stays the same but the bottom return delay increases (or do I have that backwards)?

Also, what beam angle and width do you recommend for the best discrimination between the 3 directional views?
 
Flowmotion,
It is more the port/starboard angle that changes the delay more than anything. Also what comes into play here is the temperature of the water as it will bend the beam. This will result in seeing a concave (bowl) or convex (hump) bottom when it is really flat. If you start seeing this you will need to adjust the SOS (Speed of Sound) setting.

Beam width and angle will be a personal preference. I like 40/40/40 because it lets me see the slightest bottom hardness changes in the port/starboard beams, the center beam not so much if you are looking at the tail of the primary return.

Snips
 
Back
Top