I noticed something interesting when I started using my Livescope, and thought I would pass it along.
I know many people have been wanting to know how well you can see fish that are close to the bottom. Some of you may remember when I did the thread on sonar interpretation. The same thing I described with targets getting lost in the bottom return on 2D sonar, and Panoptix, also applies to Livescope.
The big difference is its easier to see whats happening in real time with livescope and you can make adjustments on the fly by re-positioning the boat for a better view.
I can go into the technical details of exactly why this happens if anyone is interested, but I'll just keep it short for now.
Basically, if you want to see targets that are closer to the bottom, you need to be pointing the transducer either straight UP a sloped bottom or straight DOWN the slope. In either of those two cases, you will be able to see fish closer to the bottom than if you are pointing sideways or parallel to the slope.
Here is a chart of one location where we were fishing recently that has some moderately steep slopes and big depth changes. Note the red arrow is pointing more or less directly UP and DOWN the slope. The brown line is pointing parallel to the slope.
This is a screen capture that shows the bottom line on Livescope when looking down the slope. Note the thickness of the bottom return on the screen. As I went over in that sonar thread, the thickness of the bottom return varies based on how level the bottom is relative to a cross section of the beam taken at a 90 deg angle. That sounds really complicated and nerdy, but its really just a question of how "flat" the bottom looks from side to side, from the transducers point of view at any given distance. I can go into that more later if anyone wants to know. Basically all you need to remember is that pointing UP or DOWN slope gives you the best chance to see fish close to the bottom.
Now look at what the bottom line thickness looks like when the transducer is pointed parallel to the slope. Its much thicker than before. Thats because the bottom depth varies more across the transducer cone at any given distance. The extra thickness comes from the deeper bottom returns being drawn at the same time as the shallower returns at any given distance. The more depth change there is across the transducer cone, the thicker the bottom line will be.
That that extra thickness of the bottom return is where fish close to the bottom can get lost or hidden where you cant see them. The key thing is that ALL returns from the same distance get drawn on the screen.
Here is a shot from that same location looking more or less UP the same exact slope from almost the same exact position. Note that the bottom return line is back to being much thinner again.
Next time you are out fishing where there is a sloped bottom, just rotate the transducer to point in different directions and you can quickly zero in on which way the bottom slopes. I have taken to not bothering to point sideways on slopes much any more. I move the boat as needed to get a straighter shot either up or down the slope depending on the conditions.
Here are another series of shots showing how this looks when shooting up against a cliff or a large bolder or similar situation.
The first pic is looking more or less directly AT the cliff - 90 degrees to the cliff - it gives a relatively thin return.
This shot is a little further along when I was shooting at more of an angle to the cliff - notice how much thicker the cliff return is. Fish holding close to the cliff could easily be lost in that extra thickness. Re-positioning the boat for a more direct shot might reveal fish you would other wise miss.
Of course, if the bottom or the cliff or what ever, is just lumpy or irregular, then there isnt much you can do. In those cases, you're going to have extra bottom thickness where fish can get lost no matter what you do.
Hope this helps.
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Originally Posted by smbass77
