Target Separation and Target ID on the Vexilar

[little fish]

Hi,
   Can anyone explain what Target Separation and Target ID means. The FL12 Vexilar, Say's it has a 2.65 inch Minimum Target separation and a 1 inch minimum Target ID what does this mean 

  Many thx.

[Bean]

Target separation is a flashers ability to separate one target from another(think of it as one fish from another or one fish from the bottom).

Target ID is the minimum size of target(fish) it can pick up.

Some of those numbers always got me though, because I could use a 2mm jig which is really small - yet I could pick it up on my flasher.

[DasRottweiler]

Target separation is a flashers ability to separate one target from another(think of it as one fish from another or one fish from the bottom).

Target ID is the minimum size of target(fish) it can pick up.

Some of those numbers always got me though, because I could use a 2mm jig which is really small - yet I could pick it up on my flasher.

It could be the sonar is picking up the water displacement or movement directly around the jig as well as the jig.

[BigJohn]

Bean is the money.

[Mainedog]

Or it could be that the jig is much denser than a 1" fish.

[panfishman13]

that could be true, but marmooskas and a lot of other jigs are really stinkin' small

[Bean]

The flashers are actually picking up the fish's air bladder, not the whole outside of the fish.
The density of a fish's flesh is quite close to that of water and there is little reflection from the fish's outer body . The air contained in the swim bladder presents a major change in the acoustic path, which gives rise to useable amounts of reflected energy that the transducer can pick up.

[dkfry]

I never really paid too much attention to the target seperation and target ID. I just know when my Fl-18 is set up properly I can see the spikes on my jig.

[Bean]

yep. Once you've had a flasher for a while you'll know when you're bait is on or has come off.

[little fish]

Hi Bean,
           Many thanks for the answer, I always wondered what these term's meant, but did not want to ask!
        Bert.

[dkfry]

Never hurts to ask...

Vexilar has some good general info on their site you might want to look over if you havn't already.
http://vexilar.com/pages/support/support_tips.html

[Mainedog]

The flashers are actually picking up the fish's air bladder, not the whole outside of the fish.
The density of a fish's flesh is quite close to that of water and there is little reflection from the fish's outer body . The air contained in the swim bladder presents a major change in the acoustic path, which gives rise to useable amounts of reflected energy that the transducer can pick up.

But, Bean, my jigs don't have air bladders in them......

[Bean]

metal reflects acoustic signals well. Did you see that new jig the came out this year that has a concave back on it? That one will really send back a strong signal.

[Mainedog]

metal reflects acoustic signals well. Did you see that new jig the came out this year that has a concave back on it? That one will really send back a strong signal.

I'm giving you a hard time, Bean,  I've known about the bladders, but I always thought good target discrimination was helped by abrupt changes in the density of the sound carrying medium...water, air, lead, skull, brain matter, etc.

[Norman Schrader]

I have to dis-agree with the swim bladder theory. A fish is usually covered with very hard reflective scales (catfish excluded) that would give a good echo back to the transducer. The swim bladder is enclosed by these scales and the dense meat and is basically a bag of air which would absorb the sound energy.  I believe the swim bladder story got started from a number of studies of the effects of sonar signals on fish, which mentioned that the swim bladder was affected by strong sonar signals. Also, I have seen stories that LCD units detect the swim bladder and that is how the fish id feature works.  Wrong again.  All of the digital sonar have computers inside that interpret info from the transducer.  When a signal is detected that is not attached to the bottom, they will show it as a fish if the fish id feature is turned on. The grey line or multi-color units use a simple comparator circuit based on the strength of the returned echo. Fish and weeds will almost always have a weaker echo than the bottom, which the comparator will cause the display to show as a different color. I know this from experience of having been a warranty service center for a number of sonar companies over the years.

Target seperation is the ability of a sonar to distinguish between seperate objects, or an object and the bottom.  Several things affect this, including frequency of the unit, display resolution, and length of the sonar signal pulse.
Typically a 200 khz sonar could achieve target seperation of a couple of inches if the display has enough resolution to show it.

I hope this helps.
Good luck.
Norm

[dcso3009]

C&P from the Vexilar site..
How We See Fish

Sound waves are reflected by physical discontinuities (places where the speed of sound suddenly changes). The flesh of a fish is mostly water, and the difference between the speed of sound in water and in the gas of a swim bladder is so great that much of the energy that strikes it is reflected back. The swim bladder enables a fish to remain at a chosen depth without having to swim constantly to keep from rising or falling. With depth finders, you do not "see" the fish at all, what you see is the swim bladder.

Diagram of target positions in a transducer cone angleLike a bell or a column of air in an organ pipe, each gas-filled swim bladder has a natural frequency. When the impinging sound waves are at that same frequency, the swim bladder resonates and the reflection is several times stronger than other wise. The target "looks" much bigger than it actually is. To complicate matters further, the tone at which the swim bladders resonate is determined by water pressure, the size and shape of the swim bladder and the physical constraints within the fish itself. These factors change as the fish moves vertically through different pressures.

[slipperybob]

When my fluffy braid line gets air bubbles on it, that looks like I've got a hundred fishes dancing in synce everytime I jig.

[Airs24]

Keep the great information coming!  I don't think that I would have taken the time to research this if I hadn't found this post...  I have to give everyone in the Ice Shanty community credit for the reason I now know more then I ever thought I would about Ice Fishing...

Cheers