Thread: Dark area on side scan?

Originally Posted by rnvinc

The SI slice beam sound pulse is strongest along its "Main Axis" and weaker at the outer fringes of the SI slice beam directly under the boat ...


This weakening of the outer fringes of the SI slice beam will be more evident with the 800kHz simply because higher frequency sound wave attenuates (absorbs into the water) quicker than lower frequency ...(leaving less energy to be reflected off actual targets - especially in the outer fringes of the SI slice beam) ...

Rickie

Well done rickie.sounds like lower frequency would be best used,all the time.But look at that first picture that I posted again.on the left side,were the structure is.look at how well the fish stand out,were the weaker part of the 800kHz beam is being absorbed into the bottom.notice how bright the fish(air bladder makes a hard return) returns are in comparison to the dark bottom.If this were a 455kHz si or even a 360 image.the stronger bottom return from the lower 455 frequency would make the fish hard to see.higher frequency, not only produces sharper images, but also can ,in some instances make fish stand out,on side imaging and hopefully,someday humminbird will add some form of a high frequency chirp to 360.

Originally Posted by kosmo

Well done rickie.sounds like lower frequency would be best used,all the time.But look at that first picture that I posted again.on the left side,were the structure is.look at how well the fish stand out,were the weaker part of the 800kHz beam is being absorbed into the bottom.notice how bright the fish(air bladder makes a hard return) returns are in comparison to the dark bottom.If this were a 455kHz si or even a 360 image.the stronger bottom return from the lower 455 frequency would make the fish hard to see.higher frequency, not only produces sharper images, but also can ,in some instances make fish stand out,on side imaging and hopefully,someday humminbird will add some form of a high frequency chirp to 360.

I run SI a little darker when looking for fish to allow the fish return to stand out better against a darker bottom ...



I run SI a little brighter when looking for structure ...



Setting the unit and never touching anything is under-utilizing the features these units are capable of ...

Rickie

Good example,rickie. I would like to try 360 out on a higher frequency tho.455 seems harder to distinguish fish from bottom.lower the Sensitivity on 455.loose botton and fish, raise sensitivity,bright bottom,but hard to see fish. (Those last two picture that rickie posted,look like 800.the first picture looks like more of a softer bottom than that second one

Originally Posted by kosmo

(Those last two picture that rickie posted,look like 800.the first picture looks like more of a softer bottom than that second one

Those shots are most likely 800kHz ...

My fishing methods lean toward seeing more detail right at the boat ...

I use 455kHz in new water looking for new structure ...

Rickie

Originally Posted by kosmo

I would say ,that most likely possibly could be

I have never seen anything like this. It looked like a reverse course to me with the round thingies on right vs left and the similar depth change pattern in reverse. So, how was I or anyone else supposed to know?

May be a case of the Babinet principle in ur picture. Of course Rickie is right about beam concentration.

Originally Posted by Cane Pole

May be a case of the Babinet principle in ur picture.

Dang Tom ... I had to look that one up ...

https://en.m.wikipedia.org/wiki/Babinet's_principle

Your knowledge of theory is amazing ...



Rickie

Originally Posted by rnvinc

This one looks like the "Ghost Lines" phenomenon when SI piezoes and a DI piezo are transmitting in the same xducer housing ...


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This one looks like the DI transmitter is shut off and only the SI piezoes are transmitting ...



Rickie

Those two pictures had the di piezo turned off.one picture is 800,the other is 455.the first picture that I posted is from a 998 that has no di piezo. It is set on 800.This picture is from my Onix.si and di are both set to 800.fish show really well in the dark area...