Side Imaging - Structure on Drop Off's |
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VX asked the question earlier :- "I'm not sure about my 997, when I go down a bank I see this lekker structure and when I turn back to record the structure the unit doesn't pick it up or it shows it very different from what it showed originally. What can be the problem here ??" Side Imaging very often reminds me of the old military phrase - 'Just when you learn the answers they change the questions.' This is going to keep on happening until you literally set up 'camp' at you SI unit and drive around the dam looking at 'things' in the water, and then going back and looking at them again, and again, and again. Look at these two SI images below, which one would you rather want to fish, the nice big tree on top, or that skinny little thing at the bottom? You have to remember the basics before you continue here i.e. soft objects such as water appear darker and hard objects such as the ground and trees appear lighter as they bounce the sonar signal back better. *In the diagrams below, A is the boat/transducer, B is the structure, D the drop off, C the water and E the Side Imager sonar range.  Let's take this tree, if you pass it in such a way that you have water as a background, then it looks like the SI image on the right because there is no solid matter behind the tree, and thus the tree itself is the strongest return signal. Note: The boat in this diagram is traveling directly into the screen and away from you.   But if you are running a bit deeper, and in this case coming straight out of the screen directly back at you, this tree will look like the SI image on the right. This is because the bottom, or ground, is sending a better 'sonar ping' back to the unit than the tree itself. But what you will see is the sonic 'shadow' created by the sound wave behind the tree.  Discuss this article: Side Imaging - Drop offs |