learning video for interpreting images from si

Read here first, to learn about Side Imaging Technology
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learning video for interpreting images from si

Post by bogdan.andries » Sun Jan 11, 2009 4:17 am

Can somebody send me a video for learning how to understand the images picked from SI . I am interested to understand better to use this technology , because i do not know any lake underwater relief so i can train there.


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Post by MELYASH » Wed Apr 22, 2009 11:51 pm

There is a few good videos on YouTube from a guy called Tapout64 who is a guy who likes to fish for Crappie, as opposed to me who is just a crappy fisherman....

He explains quite a bit on how it works and what you are seeing. Think of the video you see as looking down thru the bottom of your boat with the black center area as being the distance between the transducer (bottom of your boat) and the first bit of bottom your sonar signal would reach. As you might imagine, in many (but not all), cases that might be straight down. so going straight down then fanning out to left and right is the bottom topography.

The sonar takes a very thin (think fore and aft) but very wide (think side to side) slice of the water your in. If you took a pizza pan and cut it in half and kept the round side down, and the flat center piece you just cut horizontal you would get an idea of what the fan shape of the beam looks like.

Now imagine this fan shaped beam moving forward thru the water and each 2.5" or so the sonar samples another slice of the water and the bottom. It displays that on the screen in front of the last slice and continues. The sonar beam is energy just like a flashlight so if it strikes an object the sound bouces back, and because that enerty cant go thru the object it starts to create a shadow behind it with no sonar energy returned in that area.

What is hard for some people to understand is the angle of the shadow as it relates to the sonar beams angle striking the object. A great example is the famous sail boat shot in the litterature. The forward sail (help me out somebody who sails) the one forward of the mast, while it did not reflect alot of sonar energy being a soft object, it did ABSORB alot of energy and so it's shadow is very pronounced!

In the same shot the Mast being hard, gives a strong bright return, while the open escape hatch and cockpit both

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Post by MELYASH » Thu Apr 23, 2009 12:00 am

absorb sonar energy, the hatch cause it is open and the energy just flows into the hatch and scatters in the cabin, and the cockpit because its multiple right angles reflect and deflect the sonar energy and possibly soft cushons in that cockpit would also absorb or attenuate the sound energy.

A good way to start visualizing what your seing is to maybe take a flashlight and put your hand close in front of the beam (but not over it completely) and let just the light spill out the sides. Now turn down the lights and walk slowly around the house like your driving your boat across a lake. look down and to the sides and see what your beam picks up, and more importantly look at how the shadows are formed.

Change the height of the flashlight from down around knee level, to waist level, to head level and see how the shadows shorten on some objects. You could even do this at night in your driveway or patio with a few pieces of pipe or some short lumber. After a few passes I think the display you see on your SI display will begin to make a lot more sense.

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Post by MELYASH » Thu Apr 23, 2009 1:33 am

Absorb energy, the hatch lets the energy pass thru to be reflected and trapped in the cabin, the cockpit because the right angles and such reflect and distort the energy and the cushions in there if there are any would attenuate the energy as well.

I just lost a huge chunk of writing cause I was off at flikr looking at images, and I got logged out.

Here is a great example of reading the SI, courtesy of Marine Electronics posting on flikr,
http://www.flickr.com/photos/21719579@N ... 691455670/
See how a relitively shallow but abrupt change in depth on the left, and return, shows up on the SI display on the right? A depth change of 3 feet on that creek channel widened that black bar that amount. so now you can start estimating things like depth changes based off of what you see on the black center section.

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More on interpretation

Post by MELYASH » Thu Apr 23, 2009 1:44 am

Here is a classic brush pile shot. Courtesy again of Marine Electronics
http://www.flickr.com/photos/21719579@N ... 691455670/
This can begin to show you the difference between brush and bait.

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Location: Beaufort, South Carolina

Post by RGecy » Thu Apr 23, 2009 7:48 am

Here are a few links to check out.

The best way is to definitely find some known structure and side image it. The more you use it, the better you will get at interpretting the images.





Post by WZX123 » Wed Oct 05, 2011 4:41 am

A variety of multimedia enriched videos can not only make learning fun but help make it an extremely engaging experience. Along with adding variety to the study schedule, these 2D, 3D and real life e-learning videos impart conceptual understanding in a very simplified manner that help students retain information for a long time. However, bad pronunciation, poorly organized and presented content, incomplete information etc in the e-learning videos not only hamper the pace of learning but can also deter future attempts at trying to understand the concept using online resources. Therefore, while referring to e-learning videos students should make it a point to check it for above mentioned points and only consider learning from those websites that meet the above requirements.

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