Best signalling equipment from the searchers point of view

[plumbcrazy]

First and foremost I will quote myself “This is a GREAT thread”

As I read through the post something caught my eye. About attaching a laminated card to your bag, I think this is a great idea.

I have been with a bad dive op and thought to myself when I was diving “I really really need to be on my toes and not get too far from the dive master so as not to be left behind”. I was new to the diving thing at that time. I would call the dive now, giving the same set of circumstances.

I would like also to throw something else out there. If you were to give the boat captain a brightly colored laminated paper with your gear and how you were going to use it in the event you were lost, and told him you wanted it back after the dive. I bet you would stick out like a sore thumb, he will either think you are a jerk or a safety conscience diver. Either way he WILL know when you are back on the boat.

Thanks for the thread!!

We will never know but you may have saved a life with this.

 

[weaponeer]

PacketSniffer, nice job on the SMB mods.

The great characteristic of RADAR corner reflectors is that if an RF beam hits it from any angle, it will reflect the maximum amount of RF back to the source of the beam, as compared to any other RF reflective object. It's like comparing a candle to a halogen bulb, the corner reflector being the halogen bulb, of course. Corner reflector use has been around about as long as RADAR - it's tried and true, and guaranteed to do the job.

Placing it inside and at the top of a SMB, using a heavy mylar or similar material, should work. It could be sewn/welded into place during manufacture, lying flat when the SMB is deflated, and forming the corners when inflated. Nothing says the reflector has to made of rigid material. Day or night, it would be there ready to do its job. No fuss, no muss. Now if we could just get ALL divers to carry a SMB, along with any other signaling device(s) of choice, we could increase the probability of rescue by quite a margin.

 

[PacketSniffer]

It could be sewn/welded into place during manufacture, lying flat when the SMB is deflated, and forming the corners when inflated.

Ahhh, I clearly didn't understand exactly what you were describing earlier. This would be pretty slick. Patent it and sell it. You'll diving into retirement in no time.

 

[HenrikBP]

PacketSniffer; great ideas for strobe mounting. Thanks for the pix also.

For RADAR reflection how about a piece of emergency blanket that could be wrapped around the top of the SMB? Securing it in place would be the challenge.
Of course a built in reflector would be optimal.

Henrik

 

[reefduffer]

Assuming that the idea of coating the inside of an SMB with mylar/foil improves the radar
signature enough to be worth the (I believe small) additional cost in manufacture, take it
a step further - why not do the same to the fabric that BCs and wings are made of?
Now it's 100% passive and a lot more widespread - a lot of new recreational
divers don't carry an SMB or sausage (tsk!) but they all wear a BC.

That's all supposing it does anything. As said, that needs to be tested.
How can that be made to happen? Does the OP or any of the responders
who indicated experience with radar search equipment have an opportunity
to see if an SMB/sausage with an inside mylar/foil coating improves detection?

weaponeer: What would be the dimensions of an effective corner reflector?

 

[weaponeer]

Reefduffer-

Defining an effective corner reflector is not that easy without taking many things into consideration. Foremost would be the RADAR frequency being used. The higher the freq, the better the RADAR cross section (RCS) of the corner reflector. RCS is a measurement of how big an object appears to a RADAR receiver. Double the freq and you will increase the RCS by about a factor of 4. Using a trihedral reflector gives better RCS than a dihedral reflector. Increasing the edge length of a corner reflector also increases RCS. Double the length and the RCS goes up by a factor of 16 (using a square-sided trihedral).

Considering many variables that apply, and defining an "effective" corner reflector as one that will increase RCS of a floating diver by any factor greater than "1", the best way to say for sure is to compile the variables, run the numbers, and conduct open water trials based on the most promising mathematical results. I admit that this task is way beyond my ability. If you want a good guess from me, I'd think that using a square-sided octahedral reflector (which forms eight trihedral reflectors, and gives 360 degree coverage) would definitely improve a diver's chance of being picked up by an search RADAR. Actual size of this unit, IMHO, would have to be at least 10cm side length, which would increase the size of an SMB, at least at the top where the reflector was located, by about double what is currently found on the market. All just my opinion, of course. Any engineers familiar with RF want to throw ideas into the mix?

 

[reefduffer]

See Lifeball International Corporation
Seems like there's plenty of prior art on inflatable corner reflectors,
these guys have some improvements, see their patent 4,901,081, 1990.
And they seem to have a product, although only orderable through
the federal stock system. Based in Houston.
The illustration shows it deployed, looks about 18" x 12".
I found a separate reference that suggests the USN uses them.

Also found Seamark Nunn Discount Marine Supplies: Echomax EMI 230 Inflatable Radar Reflector
Still a little big IMO but not out of the question, I suppose, for the really
serious, like those carrying beacon radios.
Also a few similar items on that same parent page
Seamark Nunn Discount Marine Supplies: Radar Reflectors

What I take away: Inflatable deployment of a corner reflector seems
to exist in current standalone products. They all seem to be substantially
larger than what you would build into a scuba SMB. But it's not clear that
they have incentive to go for much smaller size. My reading suggests
each side needs to be 2x the wavelenth to be useful, and as weaponeer
says, increasing the length increases effective size exponentially.
For these products, if it fits in a boater's lifevest pocket when folded,
why make it smaller and less effective?

I don't know the radar frequency of interest (can anyone help here?) but
it seems plausible that you could get some gain from something that fits
in the top of an SMB. What's the RADAR frequency of interest?

 

[weaponeer]

Reefduffer-

Nice weblink examples. Guess we need to search further to find something that would be efficient and effective for a diver to carry. One day we might find one integrated into a SMB. I can't imagine that the concept hasn't been explored by someone already.

 

[TSandM]

This is a simply superb thread, getting the information from the other side of the problem. Thank you all who are contributing.

 

[Cacia]

this is a very cool gadget, you could house easily.

I saw it in Outside magazine and it is just over 100 dollars

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