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I've been salivating over the si units for quite a while now but there's one thing I haven't figured out. How is it that they show shadows of structure and fish? They use sonar, not vision so obviously the shadows aren't light generated. Is the shadow an actual sonar shadow or are they software generated to give better perspective for the user?
The shadows are where the fish or trees have blocked the sound waves from hitting the bottom further out. Just like shadows you see with a flashlight.
The one important thing to remember is that it can’t show every fish in the water. Keep in mind that objects directly behind other objects will not show up. This is the reason the technology generates the shadow effect. If you see a piece of structure but no fish, this doesn’t mean there aren’t fish.
I've wondered about that myself. If the shadows are where the sonar won't reach, being sent from the transducer and received from the tranducer, how can you see the shadows? To see the shadows of where the sonar is not reaching, would you not have to be "looking" from another point of view than the tranducer?
It must be another view generated by the software?
I have no idea, I just get curious at times.
talltimber,
That's what I don't understand either. Looking at some of the images I've seen on the web, it doesn't seem possible that the shadows being shown could be sonar shadows since sometimes they appear to be on the near side of the structure. It seems it would be possible for the software to "paint" a shadow on the bottom since it knows where the structure is relative to the bottom below. The most obvious answer is that it is a sonar shadow and it very well may be but that doesn't seem to jive with some of the pics. Like you said, if the shadow is a blind spot from the transducers viewpoint, you'd have to be looking from a different perspective to see it. Keep pondering I guess.
Like this image from the Lowrance site. I swear those shadows look like they're on the near side of the pilings.
http://mediabase.edbasa.com/erez4/ca...8bef1719ab.jpg
The shadows look normal to me.Quote:
Originally Posted by TN Hillbilly
Sometimes the shadows will tell you more about the object than the picture itself.
http://i173.photobucket.com/albums/w...Treecondos.jpg
This is what they really are.
http://i173.photobucket.com/albums/w...7/000_0138.jpg
Sometimes fish make good shadows even when the boat isn't moving.
bob baldwin
bryan, texas
997c SI
1197c SI
AS GRHA GPS
Can’t speak for any other brand but they are sonar shadows on the ‘Birds.
Sonar shows basically two things: how long it took the sonar signal to go out and bounce back from some object (bottom, fish, structure…) and the relative strength of that signal when it returns. This gets graphed on the display as depth or distance for us humans to understand and either a shade of color or multiple colors to represent the relative signal strength. Sonar shadows are showing that for that distance from the transducer, there was no sonar signal returned since there was something blocking it. Since the display is showing distance from the transducer; we are in effect looking at the sonar returns from a ‘heads down’ perspective.
Does that make sense?