Some screenhots from today 5/24

**rnvinc** · 05-26-2014, 10:34 PM

Originally Posted by genec

Rickie,on 800 khz,what do first null mean?

Rickard at sideimagingsoft explains it much better than I can...

The null is a mathematical thing and in theory no sound at all is transmitted or received in that particular direction. However, in a practical transducer this silent point doesn't really exist. It is filled to some extent with sound, but weaker than in other directions. The effect of the null is a dark or dull band, usually near the middle of the sonar image.
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I think most would see this darker band in the image and think that it's simply a different bottom composition....

I wish I knew an small iota of the "wave theory" that Rickard knows...and he's a great guy too...always willing to help...

Rickie

**brush pile** · 05-27-2014, 01:01 PM

Rnvinc,
You took this screen shot and determined his SI was showing depressions on the lake floor. How did you come to that conclusion and not think they were rocks or humps. The only reason I am asking is because I don't know

**genec** · 05-27-2014, 01:08 PM

a hole leaves a dark spot whereas a stump would show shadow behind the stump,rickie will explain it better

**rnvinc** · 05-27-2014, 11:16 PM

Originally Posted by brush pile

Rnvinc,
You took this screen shot and determined his SI was showing depressions on the lake floor. How did you come to that conclusion and not think they were rocks or humps. The only reason I am asking is because I don't know

Like Gene mentioned ...a hole or depression leaves a dark spot on the edge closest to the beam...

Because the SI beam is travelling at an angle away from the xducer...the inside edge of any depression would not have any sound pulse data for it...because the lip of the depression closest to the beam travel is blocking the sound from getting down into the hole enough to show data for this area of the hole...

Imaging shining a flashlight at an angle across any dark hole...the leading inside edge of the hole would still be dark...

In sonar (2d/DI and SI)...a shadow is nothing more than a "void" ...of which there is no data....(our mind simply interprets this "void of data" as a shadow in the image)...

Rickie

**minnowtime** · 05-28-2014, 07:50 PM

rnvinc Thanks for all your helpful info.
If I understand it right with side imaging the 30 deg. angle, the signal would run aground in about 21 feet if you were setting in 10 feet of water. If this is true it would be hard to see suspended fish unless they were real close to boat.

**rnvinc** · 05-28-2014, 09:47 PM

Originally Posted by minnowtime

rnvinc Thanks for all your helpful info.
If I understand it right with side imaging the 30 deg. angle, the signal would run aground in about 21 feet if you were setting in 10 feet of water. If this is true it would be hard to see suspended fish unless they were real close to boat.

We have to remember that the 30° number is the "Main Axis" of the thin slice beam...or the strongest part of the sound pulse...(just like standing in front of a speaker...the sound is louder directly in front of the speaker and weaker at any angle away from the speaker)...

The sound not only radiates along the "Main Axis"...it also radiates laterally away from the "Main Axis" at the same time...

While your calculation is probably correct that the "Main Axis" will run aground at 21ft away from the xducer in 10ft of water...:

There are still weaker parts of the sound wave are that hitting the ground closer than 21ft (under the 30° "Main Axis" angle...and farther than 21ft (above the 30° "Main Axis" angle)...

The processor and the algorithms designed in the unit determine which echoes in the weaker parts of the sound wave are worthy of being "painted" into the image....and whether those weaker echoes should be painted as fish, structure, or bottom detail...

Rickie

Thread: Some screenhots from today 5/24

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