# Difference between plain ol' sonar and down imaging?



## The Longhunter (Jan 17, 2014)

Would someone please explain, in mostly one syllable words, what is the difference in (or what is) down imaging compared to just plain old sonar shooting an image of what's under the boat.


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## snookdoctor (Jan 17, 2014)

Down image look down under boat.
Sonar (side sonar) look to side of boat, and down too, to, tu, 2.

Down image, boat have to run over top of target.
Sonar (side sonar), target can be good way from boat, but can still see on sonar.

Hope little words help understand.


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## The Longhunter (Jan 17, 2014)

snookdoctor said:


> Down image look down under boat.
> Sonar (side sonar) look to side of boat, and down too, to, tu, 2.
> 
> Down image, boat have to run over top of target.
> ...




thanks, sorry for posting in the wrong forum.

I grasped the difference between down imaging and side imaging, my question is what is the difference between what a plain ol' sonar does looking under the boat, and down imaging.


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## fish hawk (Jan 17, 2014)

The Longhunter said:


> thanks, sorry for posting in the wrong forum.
> 
> I grasped the difference between down imaging and side imaging, my question is what is the difference between what a plain ol' sonar does looking under the boat, and down imaging.



It sounds fancier!!!


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## BoosterC (Jan 17, 2014)

Standard sonar the beam forms a cone with the apex (point) of the cone at the transducer (think a big wide bottom Christmas tree).  Everything in that cone that can make an echo is painted it on the screen.

Down imaging uses a very focused narrow beam (think a triangular sheet of paper) below the boat.  This results in very high resolution images.   As the boat moves over a tree, the screen is painted as distinct limbs and twigs with DI.  Standard sonar paints that same image as a blobs of signal.


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## suuntov (Jan 17, 2014)

A "picture" (DI) versus a "sketch" (2D) of whats underneath the boat.


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## brett30030 (Jan 17, 2014)

Di is best for structure, 2d is best for fish. That is the most general description. But that is about as useful as using the fish ID feature! LOL


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## klerchkatcher (Jan 18, 2014)

http://forum.gon.com/showthread.php?t=789321

The first image is the ol' sonar second image is down imaging.


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## JohnK (Jan 18, 2014)

Booster, it doesn't sound like DI will work without the boat moving and sonar will? I mean if the scan is a thin sheet of paper then the chart just keeps showing what it sees, not moving it will stay the same no matter how many fish and structure might be below?


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## chad smith (Jan 18, 2014)

Also think of an ultrasound you use for babies, a regular 2D ultra sound which is black and white, it only gives a vague sketch of a baby, kinda like the 2D sonar on a depth finder! You can't really distinguish bait on the bottom from a brush pile!
3D ultrasound for instance shows a great sketch and detail of the baby from the lips to the cheeks and fingers! The DI "Down Imaging" is just like the 3 D ultrasound giving you great detail letting you distinguish bait hugging the bottom from a brushpile!


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## BoosterC (Jan 18, 2014)

JohnK said:


> Booster, it doesn't sound like DI will work without the boat moving and sonar will? I mean if the scan is a thin sheet of paper then the chart just keeps showing what it sees, not moving it will stay the same no matter how many fish and structure might be below?


 You are essentially correct.   And that is somewhat true of standard Sonar.  If you are stationary over a branch, that branch just shows as a thick horizontal line across the screen.  But at least with standard sonar, it is more apparent when fish swim into the sonar cone (flasher type viewing), i.e., drop shot fishing.   

Keep in mind that images on the screen represent the HISTORY of what has passed under the transducer.  It is NOT a snapshot (everything captured in an instant) of things below the transducer.

DI doesn't replace standard sonar, it is a great compliment.


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## Jsppayne22 (Jan 18, 2014)

It has a lot to do with the frequency in which the transducer emits a signal.  Most of your electronics use the 83hz/200hz.  The higher the frequency, the better the picture/image in most cases.  The transducer gets more information in a shorter amount of time to create a clearer, more detailed picture.  At least that's how I understand it.  It's the equilvalent of frames per second when shooting higher quality HD video.  Hopes this helps.


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## Eugene Stinson (Jan 18, 2014)

Bout $600 


sorry I just couldn't restrain myself


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