FF frequencies in sonar and down (scan) imaging

[gkreps]

Wow Dave! Between you and Rob, I don't know wich one is the better computer geek ����

[Turtle135]

Wow Dave! Between you and Rob, I don't know wich one is the better computer geek ����

Rob is a pretty talented geek.

I do find these discussions on fishing technology pretty fascinating. After I posted those images and numbers something occurred to me that I can't wait to check out on the water.

[Yak Fish]

Wish I could help Bro...with my FF, the less I know the better! I have to admit the next FF I purchase will not have the DI, I actually prefer the sonar unless there is a lot of chatter and inference on the screen. Hopefully Yak Fish will chime in, he has a similar model and is pretty handy with the features.

Have you had a chance to use the chip?

Ah, missed this post, but I'll chime in. I have a similar model, maybe the next step up which off the top of my head I'm not sure the difference. You can easily solve the area that your sonar "sees" below with simple trigonometry using right triangles and sin, cos or tan functions. There was a nice chart put up, but the math is just like this: You know the depth you are in and you know the angle of each sonar beam....we'll call this angle theta. So the formula to solve the area that your kayak sees, we'll call this variable A.

A = 2 x Depth x Tan(theta/2)
Make sure your calculator is in degrees mode, not radians.

You'll get more accuracy with the higher frequency but less field of view. The DI is a rather wide beam and has good accuracy so I usually use the lower frequency sonar in Max Mode. It picks up everything. If I see something I want to take a closer look at, I'll switch to DI because the sonar just looks like a random blob sometimes. The DI can really help you see what it is. It's a luxury and you don't really need it, although I do have fun using it.

[Memory Maker]

Ah, missed this post, but I'll chime in. I have a similar model, maybe the next step up which off the top of my head I'm not sure the difference. You can easily solve the area that your sonar "sees" below with simple trigonometry using right triangles and sin, cos or tan functions. There was a nice chart put up, but the math is just like this: You know the depth you are in and you know the angle of each sonar beam....we'll call this angle theta. So the formula to solve the area that your kayak sees, we'll call this variable A.

A = 2 x Depth x Tan(theta/2)
Make sure your calculator is in degrees mode, not radians.

You'll get more accuracy with the higher frequency but less field of view. The DI is a rather wide beam and has good accuracy so I usually use the lower frequency sonar in Max Mode. It picks up everything. If I see something I want to take a closer look at, I'll switch to DI because the sonar just looks like a random blob sometimes. The DI can really help you see what it is. It's a luxury and you don't really need it, although I do have fun using it.

Bwhahahaha ........... yeah that's simple ........... maybe for those that can count to 20 without taking off their shoes ........

[J.A. Veil]

Being a nerd at heart, I actually thought about this last year and ran a few calculations. Then I realized that I may not have visualized things correctly. If the sonar waves go downward in a cone, they reflect off the bottom and return to the surface at the same angle, but the radius of received signals is now twice as large as the radius was on the bottom.

To further complicate matters, the calculations are somewhat understandable when the transducer is sitting still. But when it moves (due to drifting or paddling/pedaling) the location of the transducer when the sonar ping returns to the surface is not the same position as where the ping was initiated. After trying to visualize that, I put my trigonometry book away and went on to something else.

Also, what happens if the transducer is not pointing perfectly downward (i.e., is off vertical by a few degrees).

[Skidsteer]

... Software is your friend ... sometimes

[Yak Fish]

Being a nerd at heart, I actually thought about this last year and ran a few calculations. Then I realized that I may not have visualized things correctly. If the sonar waves go downward in a cone, they reflect off the bottom and return to the surface at the same angle, but the radius of received signals is now twice as large as the radius was on the bottom.

To further complicate matters, the calculations are somewhat understandable when the transducer is sitting still. But when it moves (due to drifting or paddling/pedaling) the location of the transducer when the sonar ping returns to the surface is not the same position as where the ping was initiated. After trying to visualize that, I put my trigonometry book away and went on to something else.

Also, what happens if the transducer is not pointing perfectly downward (i.e., is off vertical by a few degrees).

If the transducer is off a few degrees it thinks you're deeper than you are. It'll think that you're on a slope. For fun, I turned my DI transducer almost parallel with the water surface and in about 12' of water, it acts like a side imaging sonar.

[PigPen]

Being a nerd at heart, I actually thought about this last year and ran a few calculations. Then I realized that I may not have visualized things correctly. If the sonar waves go downward in a cone, they reflect off the bottom and return to the surface at the same angle, but the radius of received signals is now twice as large as the radius was on the bottom.

To further complicate matters, the calculations are somewhat understandable when the transducer is sitting still. But when it moves (due to drifting or paddling/pedaling) the location of the transducer when the sonar ping returns to the surface is not the same position as where the ping was initiated. After trying to visualize that, I put my trigonometry book away and went on to something else.

Also, what happens if the transducer is not pointing perfectly downward (i.e., is off vertical by a few degrees).

That's awesome, what you'd want to do is get multiple antennas at varying geometry on the platform with one emitting so you could piece together a 3D picture of the sea floor. Would require more processing power than a laptop but the PA guys should have the extra space and power available. Look up Synthetic aperature radar SAR or long baseline interferometry. Would need a receiver in the front, off to the side and preferably another down deep. Or you could create a single antenna that moves in as predictable pattern quickly to scan the bottom and run some type of averaging function to add the returns.