Sonar Quiz #25

Attachment 274223

(credit to 91reddog for the image)...

Rickie

The angle that the fish is oriented?

I was just at a humminbird seminar in Caruthersville mo.this weekend and we talked about this same scenario. (Rickie, I think that this may be your best quiz yet....keep um coming):ThumbsUp:ThumbsUp:ThumbsUp

I would say its a slimy catfish. to much slippery slim for 2d to read, the pulse just rolls right off it. I programmed mine not read those nasty things, Rickie may have his on the same setting!!

Because the 2d cone makes contact with the bottom above said fish ?

Or because the fish directly above it is blocking the sonar return ?

That's my thoughts I'm probably wrong lol

The fish in the DI is outside the Sonar cone of the 2d?

Think Crappiekirby has this wrapped up!

Quote:

---

Originally Posted by Crappiekirby

The fish in the DI is outside the Sonar cone of the 2d?

---

I'm with Redge on this one....I think Crappiekirby nailed it

Quote:

---

Originally Posted by short grub

because the fish directly above it is blocking the sonar return ?

---

I was thinking something along those lines, sorta ...

If you look at the 2d return signal of the fish just below the 10ft line ... they're dark red & large. Then the fish signals from 13-15ft are smaller red blotches (left of center of screen) with the ones just above the 15ft line not having any red at all. The fish showing on the DI image @ 17-19ft ARE showing on the 2d screen, they're just not returning a very strong signal ... so you only see a little patch of blue & green.
When you compare them to the DI image placement of the "same" fish images ... the DI images are clear & separated into nearly individual fish & bait balls, while the 2d image has multi-colored blotches that seem to define "size" by the closer distance, rather than simply from the return ping (regardless of distance). Could it be that the higher kHz signal of DI is not "painting" with as wide a brush as the 2d signal, therefore is able to pick up the images of the deeper fish ??

If I only had 2d and got that image ... I'd have to guess as to whether I was seeing 3 or 4 large fish or 2 large schools of Shad next to a brushpile on a hump. Again, I question the functionality or necessity of even having 2d in a unit, when DI (or SI) eliminates 90% of the "guessing game" of what's actually showing on the screen.

... cp :kewl

Ditto for crappiekirby.

They have small bladders.. air bladders that is.:Rofl

I believe the 2D cone is wider than the DI. the fish was on a slope and the 2D is level with the first spot it hits. I think this one goes to ShortGrub.

I think there are 2 possibilities.....Wilbur is close with the affect of the steep slope.......In the 2d return bottom indication is very thick and the fish can get lost in this thick bottom return.....The 2D is seeing a greater range of depth returns because it is getting returns from the front of the cone as well as the back of the cone on the drop.
The DI isn't affected as much because it is very thin front to back and won't be affected as much by the slope.

The other possibility is that the fish is further off to the side and not in the 2D cone......The Di is wider than the 2D

I can visualize this, but not sure if I stated it coherently.

Quote:

---

Originally Posted by BobB

I think there are 2 possibilities.....Wilbur is close with the affect of the steep slope.......In the 2d return bottom indication is very thick and the fish can get lost in this thick bottom return.....The 2D is seeing a greater range of depth returns because it is getting returns from the front of the cone as well as the back of the cone on the drop.
The DI isn't affected as much because it is very thin front to back and won't be affected as much by the slope.

The other possibility is that the fish is further off to the side and not in the 2D cone......The Di is wider than the 2D

I can visualize this, but not sure if I stated it coherently.

---

IMHO ... that's possible, but would depend on which kHz setting was used by the 2d and/or DI.

A 20deg 2d cone angle will only show a bottom circle reading of a diameter that's 1/3 the depth ... whereas a 60deg cone angle will show a diameter that equal to the depth. The DI "angles" are 75deg for 455kHz and 45deg for 800kHz ... so if the DI was using 455kHz, the angle of the fan shaped sonar ping would cover 1.25 times the depth and an 800kHz setting would cover 3/4 the depth.

... cp :kewl

I'm confused about the depth. The 2D is showing 11.7 ft & the DI is showing approximately 18 ft.

Someone please explain:dono

11.7' is going to be the closest bottom return......The would be the depth of the front of the 2D cone if going up a steep slope. If you look closely at the red section below the bottom return, that represents the "range" of depth the 2D is seeing. The boom of that red section is probably the same as the DI depth.

Quote:

---

Originally Posted by BobB

11.7' is going to be the closest bottom return......The would be the depth of the front of the 2D cone if going up a steep slope. If you look closely at the red section below the bottom return, that represents the "range" of depth the 2D is seeing. The boom of that red section is probably the same as the DI depth.

---

BobB, got it....Thanks...Had a memory loss there for a minute...75 years working on me....:biggrin

Quote:

---

Originally Posted by Don G

BobB, got it....Thanks...Had a memory loss there for a minute...75 years working on me....:biggrin

---

:ThumbsUpMy problem is that I think I understand it, but can't explain what I am thinking.....The words just get lost now days.....Good thing for spell check too. I used to be a great speller when young, but now am lucky if I can spell if.

Quote:

---

Originally Posted by wilbur

I believe the 2D cone is wider than the DI. the fish was on a slope and the 2D is level with the first spot it hits. I think this one goes to ShortGrub.

---

So if there were a flat bottom, same fish, but no quick rise of the bottom .would those fish show on the 2d? Have you ever heard anyone say that 2d won't lie? If it's down there,2d will show it? :donoDoes 2d have a blind spot in some cases?:dono:dono

Well, with Humminbird the I believe DI angle is either 45 or 75 degrees depending on the frequency being used, and whether it is set to wide or narrow.

The 2D is either 20 or 60 degrees, depending on the frequency being used.

So, if using the 455khz DI .....which is the most commonly used, a fish could be outside both the 2D cones.......If the 200khz 2D is being used, fish could be outside the 2D cone regardless of the DI frequency being used.

At least, that is the way I see what I have always thought.

Quote:

---

Originally Posted by kosmo

So if there were a flat bottom, same fish, but no quick rise of the bottom .would those fish show on the 2d? Have you ever heard anyone say that 2d won't lie? If it's down there,2d will show it? :donoDoes 2d have a blind spot in some cases?:dono:dono

---

Im gonna say they would show. The 2d shows 11ft. but the fish are about 17 ft. when the 2d beam hits the bottom it levels out it doesn't follow the slope.

I think it is possible that the fish could have been in the outer fringes of the DI fan beam and be somewhat missed by the 2d cone ...

However...this example would tend to follow the explaination from Airmar ... (the notable aspect being the sharp rise in the bottom) ...

From Airmar ...
http://www.airmartechnology.com/uplo...Operations.pdf

What is target masking?

There are areas within the transducer's range which seem to be invisible to the echosounder. This is know as target masking. It can happen if the lake or sea bottom drops off suddenly or contains a large rock. The sound waves will bounce off all of the sea bottom within the sound beam and return as strong echoes. The echoes from the highest point, the rock or dropoff, return to the transducer first, falsely indicating the apparent depth of the bottom. Small fish below the highest point will produce relatively small echoes which will return after the larger ones. Therefore, fish can be swimming around the sides of a large rock or a dropoff, be in the sound field, and yet remain invisible to the echosounder.

Attachment 274224

Rickie

I wonder if part of the problem is the 2d td installation? Maybe kicked up in the back?

Quote:

---

Originally Posted by kosmo

So if there were a flat bottom, same fish, but no quick rise of the bottom .would those fish show on the 2d? Have you ever heard anyone say that 2d won't lie? If it's down there,2d will show it? :donoDoes 2d have a blind spot in some cases?:dono:dono

---

Kos I believe 2d does have blind spots, on the edge of said cone, the bottom of the cone is not flat it is shaped just like an ice cream cone upside down with a round scoop of ice cream in it , so now the cone has spots that don't reach nor read bottom, 2d sonar gives bottom readings from the first contact made with the bottom

I'm not much good at explaining things, I hope I got this correct

Quote:

---

Originally Posted by wilbur

Im gonna say they would show. The 2d shows 11ft. but the fish are about 17 ft. when the 2d beam hits the bottom it levels out it doesn't follow the slope.

---

I.m thinking that not only those fish would not show, but even, let's say a diver that was six feet tall standing on the bottom and close to that sharp break, would not show on the 2d, but would be displayed on the di.what do yeall think?

Kos you are correct, my thinking is that if the diver is at a level below where the 2d cone makes first contact with the bottom he will not show up on 2d but he would on DI

here's a crude picture I did in paint real quick to kind of show my thoughts

I hope I'm correct if not I was told wrong or miss understood by my late uncle that was a sub man in the cold war era

Quote:

---

Originally Posted by kosmo

I.m thinking that not only those fish would not show, but even, let's say a diver that was six feet tall standing on the bottom and close to that sharp break, would not show on the 2d, but would be displayed on the di.what do yeall think?

---

+1 :ThumbsUp

Quote:

---

Originally Posted by short grub

here's a crude picture I did in paint real quick to kind of show my thoughts

I hope I'm correct if not I was told wrong or miss understood by my late uncle that was a sub man in the cold war era

---

so if this is the case, when traveling perpendicular to a sharp dropoff and you see fish returns, can you assume the fish is on the leading edge of the cone since the rest is dead zone?

:scratchhead

Quote:

---

Originally Posted by short grub

here's a crude picture I did in paint real quick to kind of show my thoughts

I hope I'm correct if not I was told wrong or miss understood by my late uncle that was a sub man in the cold war era

---

I don't agree, but I've been wrong many times, just ask my wife. If this was the case why would the sound waves travel in a circular pattern? With the technology now they can direct the beams, just look at down and side scan. Also the rest of the signal continues and bounces off and is returned to the td. Now what the processor does with I don't know. I believe that if a 6' diver was standing at the bottom of the drop he would show up, I've seen to many bucks and beds right at the bottom of drops on 2d and down scan. Surely if you can see a 5 gallon bucket with some sticks at the bottom of a drop you could see a man. No disrespect intended, just my opinion.

I'm sorry my illustration is for 2d

That's the way I took it, I just made the reference to ds and ss to point out what can be done with cone shapes. Sorry if I wasn't clear.

This idea of "target masking" seems like it would only come into play if the boat were moving from deep to shallow up a steep slope or ledge...(how steep...?? I do not know) ...

This would cause the front edge of the cone to contact a rather reflective surface (the upsloping bottom) before it contacted any "fish type" targets under this point ...

The sonar processor algorithms looks for a certain "repetitive" echo that it can define as "Bottom" ...

Then ...any echos (in that same ping) that are farther away than the "Defined bottom" are disregarded ...

Attachment 274225

Rickie

Quote:

---

Originally Posted by rnvinc

This idea of "target masking" seems like it would only come into play if the boat were moving from deep to shallow up a steep slope or ledge...(how steep...?? I do not know) ...


Rickie

---

This just doesn't seem right.....we know the boat (and the transducer) were in motion. Otherwise we would have a horrible pic. So as the cone moves from deep to shallow, the leading edge of the cone will "see" the fish from the tail to the back to the front and begin making an arch (2D). The targets would not be disregarded because they would start to appear as the angular cone picks up the fish above the current "bottom" that the cone is seeing. If there is masking, it would have to occur when the leading edge of the cone reaches a point above the fish. This may cause a cut off arch, but surely not complete masking. Remember, the point defined as the bottom in this illustration was below the fish and then moved into this position. It's my belief that the true masking would happen when the boat is moving parallel to the drop off

Check this link out. Talks about the"dead zone".

Use your fish finder to locate the structure that holds fish.

Quote:

---

Originally Posted by vic n

This just doesn't seem right.....we know the boat (and the transducer) were in motion. Otherwise we would have a horrible pic. So as the cone moves from deep to shallow, the leading edge of the cone will "see" the fish from the tail to the back to the front and begin making an arch (2D). The targets would not be disregarded because they would start to appear as the angular cone picks up the fish above the current "bottom" that the cone is seeing. If there is masking, it would have to occur when the leading edge of the cone reaches a point above the fish. This may cause a cut off arch, but surely not complete masking. Remember, the point defined as the bottom in this illustration was below the fish and then moved into this position. It's my belief that the true masking would happen when the boat is moving parallel to the drop off

---

Yeah ... wouldn't the fish be "seen" by the 2d cone (front edge) BEFORE it started climbing up the ridge, and just be images in the history of the screen scroll ???

:Rofl ... ya'll are just making my point about 2d being somewhat a useless technology, when it's paired with down scan imaging.

... cp :kewl

Quote:

---

Originally Posted by apersohn17

Check this link out. Talks about the"dead zone".

Use your fish finder to locate the structure that holds fish.

---

And I feel this sort of reinforces what I said. This author states: "A 2 dimensional display can only show the shallowest reading it is receiving back." and his illustration shows a boat sitting over a dropoff, but not showing the fish that are below the "shallowest reading". But remember this is NOT a static picture. This boat is moving from left to right. The transducer will go from shallow to deep as the boat moves, so the "shallowest reading" will gradually go deeper and deeper, and then start showing those fish on the downslope, altho the fish would probably form even less of an arch than if the boat were moving from deep to shallow as in Rickie's illustration. If the boat in the illustration remains in ONE place, then it will show a flat bottom with no fish.

Quote:

---

Originally Posted by CrappiePappy

:Rofl ... ya'll are just making my point about 2d being somewhat a useless technology, when it's paired with down scan imaging.

... cp :kewl

---

I'm not much good at finding or catching fish, cp, but I have started using a split screen with both 2D and DI when I stumble onto a brushpile. The DI gives me that true picture quality, but when I want to ease in close, the 2D tells me when I'm getting there by showing echos coming from the front edge of the cone.

The actual sonar image that Rickie posted with the question demonstrates the issue.....The boat was moving up the slope in that image.

I am just hard to convince, but I still think it is outside the 2d cone. If boat were running parallel to the slope you would see flat bottom on the 2d. Also there are some weak returns in the area which would indicate the edge of the 2d being received.