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Old 09-15-2017, 01:58 PM   #33
chris138
donkey roper
 
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Join Date: Apr 2009
Location: Pacific Beach
Posts: 968
Quote:
Originally Posted by Dirty Curti View Post
Great info thanks.

This is near the pipe in carlsbad.

Your comment regarding the "big worm" in photo 4 is to soft to be a fish. That confuses me because this is what I would expect to see if there is a larger fish under the kayak. So you said that if it was a bigger fish in water that shallow that I would see bright yellow color in the mark?

Also, Is there a way to understand a mark being on the left or right side of the kayak? Or where you should be casting when marks show up?
Yes. The purplish return that you see there is probably some kind of kelp or debris floating midcolumn. If you were in 140' of water and saw that mark, I would say it might be a fish. But for how shallow you are in that pic, and how high your gain is set, a hard-bodied object would come back yellow, if not bright red/orange. Some may disagree with me... it's only my opinion.

You really can't tell which side of you the fish is on for the most part. I should note that its not impossible to tell, but its a very advanced technique without sidescan. The technique must be done with dual frequency, and requires a sideways oriented drift. The two sonar cones are not identical, and you can infer information from the overlap of the two signals. So if you drifted directly over an object (assume it's stationary) it would show up on 83 kHz first, then it would show up identically hard on both frequencies, then disappear from 200 and only be on 83 again. At this point you would know the object was on the upwind side as you drifted directly over it. If you practice this technique often, you can start to predict when the object will take this path. So once you just barely start to get the return on 200kHz, you can infer that it is down-drift from you.

Anyone follow that?

You can also slowly zigzag across an area and make similar inferences. Like I said, it's an advanced technique and takes 100's of "sonar hours" to be effective.

I had an idea for an invention which would have a dual spectrum return that could differentiate between port and starboard orientation. Anyone know an acoustic engineer?
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