What details in the following image give indication of bottom hardness/softness ...??
Explain what is happening to the sound pulse (ping) for that echo data to be "painted" as seen in the image ...
Attachment 274182
Rickie
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What details in the following image give indication of bottom hardness/softness ...??
Explain what is happening to the sound pulse (ping) for that echo data to be "painted" as seen in the image ...
Attachment 274182
Rickie
I see a second and third trip of the sonar pulse depicted.Quote:
Originally Posted by rnvinc
The hardness/softness can be seen via the color bar or the harder bottom will continue to show in the 2nd and 3rd echo shown.
Is that what you are looking for Rickie?
May be wrong on this but we learn from our mistakes :biggrin
Looking at the screen shot I would also think you have more of a peegravel bottom than slab rock with silt based on the thickness of the red return. The multiple bottom returns are from the echo of the pulse, I think I said that right...
I believe what causes the multiple returns is the transmission reflecting between bottom and water surface. The hardness of the bottom is indicated by the color palette. In soft bottoms too much of the transmission is dissipated to provide multiple returns. There is also some transmission loss each time it reflects from the surface of the water back down.
http://i826.photobucket.com/albums/z...psr3jrtd72.png what happened here
In the pic it is a double and triple echo from the original return. Each will be less clear as it repeats. If the bottom depth was set at 150 you should see two more returns and get less clear. I have heard that catfish will not show up in the double echo because they have no scales and that scaled fish will show up on the second echo. As far as the bottom in the original signal, it appears to be a thin harder layer with a softer layer underneath.
Where the echo is missing in the second and third time around is the softest bottom in the first time echo. Where the echo is hardest will keep showing up in the 2nd and 3rd echo.Quote:
Originally Posted by kosmo
I can tell some of you guys remember the "2nd Echo" from the flasher days ...
Attachment 274185
Remember ... The 2d display must be set to a lower range that allows enough room on the display to even see the 2nd echo ...(and multiples thereof)...
That is ... If bottom hardness/softness is something you want discern in the 2d image ...
Attachment 274197
Rickie
Check your saved 2d snapshots ...
If you have any examples of the 2nd echo ... Post them here for everyone to see ...
Rickie
Can a person, using di, tell the bottom hardness?????
Rnvinc I liked Slabbacks answer of the pea gravel, do you know what the bottom actually was?
Thanks I learned something new!
Good questions Kosmo, looking forward to the DI answer.
The image I used was a stock Humminbird image ...so I wouldn't know the actual bottom composition ...Quote:
Originally Posted by Redge
Rickie
I would say "somewhat"...Quote:
Originally Posted by kosmo
In the image below (also from Doug) ...we can definately see in the DI image the same "brightness" of the harder bottom that is seen in the SI image ...
Attachment 274187
1 point to remember in the above image is this is "DI from SI" ...which is the same data - just rearranged in the DI image ...
Rickie
Thanks rnvinc, I don't use 2d much, maybe 1% of the time. I liked the pea gravel, because it had the thin red line on the top of bottom. I really appreciate the quiz posts. Sometimes I can't ask the question, because I don't even know what I don't know!!
That's as clear as a silt bottom! LOL
I would have expected the thin red line to change to a lighter color at the transition ( B1 ) Learn something new everyday.............
I believe you can tell the difference between hard and soft bottoms on DI. I know you can see when it changes.
Sure can but you must have your contrast set correctly or you will bloom it out and not be able to discern the difference.Quote:
Originally Posted by kosmo
I try to keep my contrast set about 70% unless I'm real shallow. (Lowrance HDS)
rnvinc here are two shots for you. This first one I know to have peegravel due to using a jigging spoon and coming up with small gravel in the hooks when I let it hit the bottom and jerk it back up. Also I use break rotors from a truck as a anchor and have small chunks stuck in the grooves.
http://i29.photobucket.com/albums/c2...ps29936ef1.png
In this shot it's a compacted mud flat...the anchor comes up with a cloud of gunk lol. This was the reasoning for the earlier post in reference to the peegravel. I have a lake that is shell rock and should have some shots in 2D in one of these files. When I find one I'll post it as well. The RED line is much thicker in those shots.
http://i29.photobucket.com/albums/c2...ps48573059.png
Found one. (look over the writing, it's from a earlier post) This bottom is shelf rock that drops off.
http://i29.photobucket.com/albums/c2...pse0c201e5.png
Can anyone see the sediment build up and why would it be there?
I would have thought the red line would have gotten thinner or changed colors as it transitioned from hard to soft bottom. Was this a function of the under lying layer transitioning while to surface layer remained the same?
cookie I can only go off what I've seen while on the water....that question has rnvinc wrote all over it. If anyone will be able to tell you, he can.
Most of the Original Pallette snapshots I can find seem to always have the thin red line as the 1st reflection ...Quote:
Originally Posted by lcookie
Then a thicker red line (as seen in the mid section below) would indicate larger rocks (or a shale layer as slabbacks referred to) ...
The thick red line in the below pic may even be a rock pile (from the shape of the return in addition to the thicker red line)....
Attachment 274199
I think cookie may also be correct in that the underlying layers may have something to do with how much of the pulse is reflected ...which would attribute to the multiple echoes we saw in the OP image ...
Rickie
Rickie to the right side of your shot (OP) where the brush and fish are, could this be (for a lack of better terms) sucking up or blocking the beam from reaching the bottom which would account for the weaker returns shown by the other layers in that shot?
That is a possibility slabbacks as anything that reflects some of the sonar is also blocking passes by or through it from reaching anything underneath it as well. However I would expect that most of that is due to a softer bottom in that area. We see where some of that fish/structure area reflected enough sonar to produce a second sonar return, so that spot was harder than what was directly before and after it.
Some things to keep in mind here are not only the color pallet being used but also the sonar frequency, beam width and any menu settings that can affect how the bottom is shown (Sensitivity, any sort of WhiteLine or filtering, TVG or surface clutter settings). Even things like the shape of the bottom terrain can affect how thick the red line is shown. In Rickie’s last pic above; some of the reason for the thicker red line in that area is due to the shape of the bottom. With a slope/drop-off the sonar is receiving a strong sonar return from more than one water depth at the same time and so shows this as a thicker red line. If the same bottom were flat it would show as a thinner red line. Remember, the sonar will try and show all sonar returns from the circular sonar beam and while over a slope it is receiving sonar returns from the shallow, middle and deeper ends at the same time. If they are all of the same density, they would all get shown as a thicker layer or line as the deeper end of the slope is farther away from the transducer – which gets shown as a deeper water depth for us. Of course, a slope or drop-off reflects less sonar directly back to the transducer and so should get displayed as a weaker sonar return color and would be unless the Sensitivity of the unit were turned up too high to show this. Of course when you turn down the Sensitivity in your unit so that it does show this (or even to the point that it could show the difference between bottom types); you may have also set it so low as to not show any fish, which most would never do.
Greg,
Good point on the rise and fall of the bottom causing the thickness to change given the multiple returns from different elevations.
Thanks Greg for the info. What I was taking as a bottom composition change may actually be a result of angle of the return then. Good read, thx again
Has anyone ever seen a multiple return from a thermocline?
Seems like I remember someone posting a double thermocline somewhere ...Quote:
Originally Posted by ezfishn
I'll have to see if I can look it up ...
Rickie