Search and Rescue - Lasers and Signaling Devices

[JohnnyC]

Is a PLB guaranteed to give your location ? That seems to be the ideal solution

Yes. It transmits your GPS-derived location when you activate the emergency beacon functionality of the device.

 

[-JD-]

Note: Originally from the PLBs Can Save Your Life thread, but this linked author has relevant information that includes (and crosses boundaries between) General SAR/Survival, Visual Search, and Radio Distress Devices so I am x-posting in these related threads as well:
- Search and Rescue - Lasers and Signaling Devices
- SAR network - an idea.
If you haven't been following the other discussions in the group, it might be worth your while to look at them for a more rounded take on the various aspects.

Mario knows what he's talking about. He was a rescue swimmer in the USCG for a long time and now makes quite a bit of their equipment as a contractor. And his blog is worth reading.
EPIRBs Do Not Save Lives

Thank you for posting this!!!!

His articles (main lists here: Articles, Blogs, and Rants & https://www.soundingsonline.com/voices/lifelines-safety-and-rescue-at-sea) are a great resource covering multiple aspects of Sea Survival & SAR.

I'm pulling out a few specific ones here that I found to be very relevant to the ongoing discussions ...
Radio Distress Devices:
- EPIRBs Do Not Save Lives (article originally linked by @rjack321)
- https://www.soundingsonline.com/voices/epirb-ais-satellite
- https://www.soundingsonline.com/ask-mario-videos/ask-mario-epirbs-vs-satellite-tracking-devices
Visibility:
- Over Here! Being Found is About Being Seen
Survivability:
- Giving Up: Why the Coast Guard Quits Looking
- https://www.soundingsonline.com/voices/cold-hard-facts

 

[BlueTrin]

Yes. It transmits your GPS-derived location when you activate the emergency beacon functionality of the device.

And the whole world is covered by this mechanism/frequency ?

 

[JohnnyC]

And the whole world is covered by this mechanism/frequency ?

Yes. International Cospas-Sarsat Programme - Wikipedia

 

[-JD-]

And the whole world is covered by this mechanism/frequency ?

Lots more discussion of PLBs (and AIS/DSC radios (like Nautilus Lifeline) over in this theread: PLBs Can Save Your Life

 

[Rred]

"Is a PLB guaranteed to give your location ? "
NO! Nothing is guaranteed to connect to any satellite communications. There have been defective EPIRBs from top names that simply did not transmit--even when they showed a confirmation light. And depending on which satellites are overhead, the system can take an hour or two to find your location. A third generation of satellites promising faster, more precise, wider, coverage is in the process of being added.
Still, a PLB is probably "the most likely" way to get a message out, from the most places, in the shortest time. It doesn't substitute for other ways to connect locally--if there's anyone out there.

 

[tursiops]

And the whole world is covered by this mechanism/frequency ?

Yes, but there may be delays at high latitudes, because the polar-orbiting satellites that can see PLBs at high latitudes have 102-minute orbits, so there may not be one overhead at any particular moment. in addition, there may be a delay in getting your emergency transmission relayed to ground, because the satellite has to get over a ground station to downlink your distress call.
NOAA - Search and Rescue Satellite Aided Tracking - Welcome
NOAA - Search and Rescue Satellite Aided Tracking - Future Enhancements

 

[dmaziuk]

"Is a PLB guaranteed to give your location ? "
NO! Nothing is guaranteed to connect to any satellite communications. There have been defective EPIRBs from top names that simply did not transmit--even when they showed a confirmation light. And depending on which satellites are overhead, the system can take an hour or two to find your location. A third generation of satellites promising faster, more precise, wider, coverage is in the process of being added.
Still, a PLB is probably "the most likely" way to get a message out, from the most places, in the shortest time. It doesn't substitute for other ways to connect locally--if there's anyone out there.

It's one of the basics of computer communication, known as the "two army (or two generals) problem". The Internet connects using a "three way handshake" solution that works well enough for the purpose, but in general it is unsolvable: the only way you know is when your rescuers tell you it was the PLB that led them to you. Look it up on wikipedia if interested.

 

[tursiops]

It's one of the basics of computer communication, known as the "two army (or two generals) problem". The Internet connects using a "three way handshake" solution that works well enough for the purpose, but in general it is unsolvable: the only way you know is when your rescuers tell you it was the PLB that led them to you. Look it up on wikipedia if interested.

Interesting, but probably not the crux of the problem, in practice.
The information flow is:

You are (1), with your PLB. The chances that your distress call gets to (2), and 93), and (4), are very high. The step to (5) is more flaky, and (6) might be almost nonexistent. You can help (5) a lot by filing the appropriate info about where you are going to be diving, but you can't do much about (6). Some PLBs apparently can receive the purple return link, to let you know your signal got through. Nice, but it doesn't change (6).

 

[dmaziuk]

Some PLBs apparently can receive the purple return link, to let you know your signal got through. Nice, but it doesn't change (6).

Correct, what we need for the networking is after receiving the purple link to send the acknowledgment back via (2) - (3) - (4): "I heard that you heard me". In this application we do care about (6), of course.

(Possible use case here could be to save the battery and stop transmitting for a couple of hours -- or until a "where are you?" message comes over the purple link.)