Thread: humminbird greg

Maybe this will help with your ratio question...



Rickie

Am I reading this right in that the down imaging has a wider band than the 2D sonar?

Yes, wider left to right but VERY MUCH thinner front to back. So when moving forward a piece of structure under the boat will show on your 2D sonar before it will show on your DI image. But a piece of structure farther out to the left or right will show on the DI but may not show on the 2D because it is out of the cone coverage area, and you won't know what side of the boat it is on.

Originally Posted by blairarnold

Am I reading this right in that the down imaging has a wider band than the 2D sonar?

Yes ... Kenny is correct in that a 2d signal produces a circle, while a DI produces a fan shaped cone. A 2d sonar is giving you a 2 dimensional picture of what's within the cone. A DI sonar signal is producing slices thru the water, giving you a closer to 3 dimensional picture. The cone angle degrees are relative to the signal strength, along with the (shape) side to side & front to back width of the coverage area.

The illustration that "rnvinc" has in his post, shows you how each signal is shaped. Take special note of the "Top View of Sonar Beams" illustration ... that shows you what the difference in shape & area coverage is, of a 2d cone (circle) vs a DI cone (fan). The Area of Coverage menu tells you that a DI cone has 3-4 times the left to right angle of coverage, but only 1/3-1/4 the front to rear angle of coverage area. (I believe the front to rear angle is something on the order of 6 degrees of angle).

If memory serves me ... a 60deg cone angle is the widest there is on a 2d unit (triple 20deg cones). But even then, the units are only able to give you a 2d picture. DI units are "scanning" with their narrow depth/wide width cone, and the higher processor power of those units can composite a more 3d version of the signal ... translating the return signal into more of a "picture", than a "representation" (like what you get with the pixel collection of a 2d unit). It's also why DI units need to be moving forward, in order to get the scan info from different angles, and "draw" the more detailed image on the screen.

The more power the unit has (kHz) in the output, and the smaller the pixels (more pixels per given area) ... the more detailed the screen image can be.

* that's the way I understand it, anyway !! I'm no expert on anything, and don't claim to be

... cp

These guys explained that very well..

I would offer to add... Always consider that sonar is not a "camera" looking down into the water..It's a sound wave transmitter..

Everytime the unit "pings" ...a sound wave (in the shape of the specific beam angle) is sent thru the water...

Echos received in that "ping" are processed and "plotted" onto the unit's screen in a thin strip (a few pixels wide) to the far right of the 2d or DI screen...

The very next "ping"s echo data is processed and plotted onto the far right of the screen....pushing the previous "ping" data to the left...

This "stacking" of echo data into strips onto the far right of the unit screen ...is what "builds" the screen image on the unit screen...

The only data showing on the screen image that is currently under the xducer.. Is the strip at the far right of the screen... Everything to the left of that thin strip on the screen is "history" that the xducer has already passed over...(and no longer in the sonar beam)...

Rickie

Thanks for the answers. You all have taught me a lot. It's always a good idea to deal with people smarter or more knowledgable than I am.

Originally Posted by blairarnold

Thanks for the answers. You all have taught me a lot. It's always a good idea to deal with people smarter or more knowledgable than I am.

Not 'smarter'.....just ....

Been there, done that....with the same questions you have......

Questions is how we all learn...keep asking...

Rickie

thanks i needed to know that.