Sonar Marker help needed

[sportscanuser]

I am looking to construct two cheep ,simple, light weight reusable sonar markers that I will use to pinpoint the location of a object on a side scan images so as a diver can be sure landing right on the target, my plan is to deploy one of the markers as close as possible to where I think object of interest is, re scan the target getting both target and marker in the one image and then deploying the second marker right on the target and rescanning to confirm this, then diving down using the marker buoy as a type of shot line or put a camera down to view the target with minimum time lost . What material will be light and give a good sonar image any suggestions. Max depth will be 100ft.Has any body already done this?

[munromh]

beans

Although I have not had the opportunity to test it I've thought should the need arise that I would use a standard aluminum radar reflector. The setup would be configured from the bottom up to have a weight, a short piece of line, the radar reflector, another short piece of line, a small buoy to keep the radar reflector off the bottom, and then a line to the surface with another buoy. Depending on tidal conditions the weight and float sizes would have to be adjusted. But even with the reflector on the bottom I think it might be effective. I imagine a specular reflector like a round ball resting on the bottom would be effective as well ... or:

http://www.marine-group.com/SonarPri...htm#Reflectors

A typical example is the STARR (http://www.marine-group.com/SonarPri.../a1arefex3.gif) retro-reflecting sonar target, a specially constructed, buoyant target which reflects a large percentage of the incident sonar energy back towards the sonar transducers. The sonar's side lobes help the interpreter identify the existence of a retro-reflecting target while the returns from the main lobe show precisely where the target is in the underwater environment. Targets like the STARR are used as a benchmark in marking portions of seabed for programs like seabed monitoring. They are also used in combination with a surface buoy to determine the exact position of a seabed feature that must be sampled or examined.

[John B]

Sonar marker

You could probably use an array of 8" plastic fishing floats "moored" close to the bottom without any radar reflector at all. The air in the floats will reflect sonar well. You may have to experiment with the number and arrangement of the floats but I'd guess stringing 10 or more in a loose bundle would be a good starting point. If you can find them, old aluminium floats might be even better.

[UWLocator]

What Works For Me

I find that anything smaller than 12" in diameter can be hard to spot on some scans. I now use empty freon containers that are obtained from A/C repair shops for free.

I drill a series of 1/2" holes starting about 1/3 of the way down from the top. I usually drill about 20 holes between that point and the bottom so water can fill the lower 2/3 to reduce the lift. I attach one to an 11lb. mushroom anchor with a 2' long 2" diameter rope then I put a second one on the first with the same type and length of rope. From the second one I attach 1/2" rope to a movable float on the surface.

I find those targets easy to pick out with all of the sidescan units that I work with. On the Marine Sonic unit, I can even see the 2" ropes.

If you go this way, be sure to paint the inside and outside of the bottles. I have some that have been used for at least 10 years and still have not rusted out.

Good luck,
Rip

[49thdiver]

sonar markers revisted

Just joined and found this thread that seem to have run out.
For similar reasons as the original posting I have been thinking about underwater reflectors. The reflectors I would like to put down would be semi permenant, and with NO surface marker. The reason for no surface marker would be so they would not get dragged away by log booms, boaters not paying attention and not to mention less then honest fisherman that think they are pulling someone elses traps. I use a GPS to find my sites but would like a sonar marker to pin point the sweet spot. I like the idea of the freon containers, but am not sure how long they would last and wonder how environmentally clean they are. along this line would old aluminum 80 scuba tanks work.

It would be realitivly easy to secure lead weights to each end so they laid parallel to the bottom making a bigger better target. One could weld sheet material on them if it actually reflected the sonar pulses back. But I tend to think the air in them would work just as well. It would look like a BIG fish.

Any fresh idea's would be appreciated.

P.S. This is a very cool forum, I look forward to participating more.

Thanks