I took a look at radar-reflective SMBs a couple of years ago as a result of some suggestions in this very thread, which I wrote up here:
http://www.scubaboard.com/forums/re...3968-radar-reflective-smb-safety-sausage.html
One of the things I found searching around the web was this:
The Rescue Wing: Design of a Marine Distress Signaling Device.
Tomas Melin and Sandi Sefi
Royal Institute of Technology, Stockholm Sweden 2005
Proceedings of IEEE OCEAN2005, Washington DC, USA, September 2005.
PDF downloaded from
OutBox page for Sandy Sefi
Sort of a combination balloon, kite, visual signal, and radar reflector. Sounds like a great concept, and very applicable to scuba diver rescue, but looks to be so far just just an academic exercise, no product. But the discussion has some more useful discussion of requirements, and some useful references.
I wonder if there's any connection to what Thal mentioned.