SI v/s DI for fish

I have a question for the SI-DI experts out there:
Do you see fish on SI that are missed with the DI?
Question is, in viewing fish in troughs (dunes on pool 4), you will find areas on the SI that are absolutely stacked with fish in deep enough water that you could drive over them and not spook them to the side of the boat. When I drive over these areas with my DI, majority of the fish are not marked (very easy to replicate due to dropping an icon-waypoint on the SI).
My question is: does the SI see fish that the DI misses due to “seeing them from a side profile” v/s the DI looking straight down and missing them due to the fish (saugers probably) being tucked right on the bottom?
I know that fish tucked on the bottom are missed with 2D due to target seperation, would this also be the case with the DI?
I imagine it would be easier to get a good side shot at the fish v/s a down shot–which is true with any medical imaging device(reason for different views).
Since I did not have a fish camera along, I was unable to drop a camera down there and look, that would have told the tail.
SI-DI rocks!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Jeremy

Just a second….let me dig out some DI images from the library.

I’m definitely not an expert, but I’ve read here and elsewhere (check out the Doc Sampson article in current In-Fish) about the limitations of a beam shooting straight down. In the situation you described, there are blind spots because of the beam being intercepted by the top of the dune. Think of it as a flashlight and how there will be shadows in certain areas as you move through.

Anyway, I know you’ll get a better answer but to me it seems very possible that you’d see the fish with one beam and not the other. I’m thinking you ought to check for the fish with a camera (or a rod and reel!) if you really want to confirm.

The Humminbird SI and DI sonar is described as a “razor thin beam”, which is what gives it the ability to paint picture-like images of bottom and structure, and not “blob-o-grams” like you see with traditional 2D sonar. As a result, I suspect that blind spot issues are negligible with Down Imaging as compared to 2D (single or dual beam) sonar.

Doc, to address your question:

I can see fish simultaneously in SI and DI, as well as DI and 2D. Here are a couple of examples.

First, here is a big pile of fish from this fall. These were right out in front of Mr. Sippi. Notice that fish are visible in SI off to the sides, in SI right under the boat, as well as in DI.

Here are some wingdam-related fish, in SI, DI, and 2D. Again, visible in SI, visible in DI, and visible in 2D.

Here’s a larger fish, over a rocky bottom, in 2D and DI.

Here’s a screen capture that addresses your original question: can you see fish with DI in the troughs of the whoopdies.

Answer: yes.

Maybe I am just seeing so much more on SI? I am seeing them on DI, just not the numbers I would expect, but I am seeing them like your dune shot; i.e.is it more likely due to the beam being so much narrower on DI?

What is your DI range set at (narrow/medium/wide)?

I run mine in “wide” most of the time.

Jason, I bet you’re right that what I was reading compared traditional 2D sonar to the side imaging. I’ll have to revisit and/or read more about the DI.

I love the images showing big schools of fish. Did you catch any of those fish in the WI channel last fall?

I’ll check the settings for DI.
the rest are just where you left them!!!!!