B Which technique has been used? (drowning victim recovery in a lake)

[fresh_42]

TL;DR Summary

This happened last week on a mountain lake. They solved a drowning problem with the help of specialists but didn't reveal their technique. Which one could it have been?

Last week, a family of four rented a paddle boat on a mountain lake, 1.77 sq km large, 15 m average, and 36 m maximal depth. In the middle of the lake, their 6-year-old son fell into the water and drowned. His father jumped in for rescue, and neither of them surfaced again.

The lake was about 30 m deep at this point, with strong underwater currents and rocky ground. All usual methods to find the two failed: divers, dogs, helicopters, and sonar. It wasn't before they asked a certain company for help that actually managed to locate the two bodies at a depth of 24 m. Unfortunately, there were no reports in the news of what technique this company had used that other institutions could not.

My question: What was it that this company used to succeed where others had failed? What can distinguish between fish swarms, rocks, and human bodies? Any ideas?

 

[renormalize]

My question: What was it that this company used to succeed where others had failed? What can distinguish between fish swarms, rocks, and human bodies? Any ideas?

Side-scan sonar? Remotely operated vehicle (ROV)?

 

[A.T.]

What was it that this company used to succeed where others had failed? What can distinguish between fish swarms, rocks, and human bodies? Any ideas?

Doesn't the company have a website, where they advertise their services? From the vague description it could anything, from diving robots to a crystal ball. Maybe they simply had a better sonar, or a sonar mounted on a diving robot that scans the lake bed more systematically. Or they used the knowledge about the currents to simulate where the bodies most likely drifted to.

 

[fresh_42]

Doesn't the company have a website, where they advertise their services? From the vague description it could anything, from diving robots to a crystal ball. Maybe they simply had a better sonar, or a sonar mounted on a diving robot that scans the lake bed more systematically. Or they used the knowledge about the currents to simulate where the bodies most likely drifted to.

They didn't even mention the company's name, only its hometown, which is too far away to have data about currents that only occur underwater, that the local SAR teams didn't have. Those currents have basically been detected by the divers involved in the operation. The news also didn't mention an unmanned vehicle, so it is almost certain that it was a specific sonar. So what kind of sonar (or EM waves) allows us to distinguish between biological masses (and not fish) and rocks?

The vague description is the reason for my asking. Otherwise, I could have figured it out myself. Nevertheless, I think it is safe to say that it wasn't a crystal ball.

 

[A.T.]

So what kind of sonar (or EM waves) allows us to distinguish between biological masses (and not fish) and rocks?

I'm no expert. But it might just be a more systematic automated scan, combined with a more effective signal analysis, eventually using AI.

 

[fresh_42]

That's all I could find:

This is a company that specializes in underwater technology – and apparently has more powerful equipment than the police forces. The experts managed to locate the bodies underwater late Friday afternoon – just a few hours after arriving at Lake Eibsee.

 

[DaveC426913]

Unfortunately, there were no reports in the news of what technique this company had used that other institutions could not.

Have you considered directly asking the reporting news org for further details? Worst they can do is say no.

 

[kuruman]

It could be something low tech such as going to the approximate spot on the lake and dumping a sack of potatoes or equivalent with a long string attached to it. Then send a ROV to follow the string.

 

[fresh_42]

Have you considered directly asking the reporting news org for further details? Worst they can do is say no.

Most reports I have found were factually based on one report from the German press agency (dpa) and were rather general, with no individual research. After all, it is simply a message about an ordinary bath accident, tragic but not rare.

I was just wondering about which version of sonar exists that would allow such a very specific detection that an ordinary sonar, which had been used prior to that, didn't have.

 

[fresh_42]

It could be something low tech such as going to the approximate spot on the lake and dumping a sack of potatoes or equivalent with a long string attached to it.

Seriously? You have no idea at all, but it was a pleasure to talk to you.

 

[256bits]

Most reports I have found were factually based on one report from the German press agency (dpa) and were rather general, with no individual research. After all, it is simply a message about an ordinary bath accident, tragic but not rare.

I was just wondering about which version of sonar exists that would allow such a very specific detection that an ordinary sonar, which had been used prior to that, didn't have.

Side scan sonar.
See post #2 @renormalize

 

[Dale]

A body would have a less dramatic change in acoustic impedance than a rock or even wood. So you could probably make that distinction by analyzing the strength of the reflection.

 

[DaveC426913]

Seriously? You have no idea at all, but it was a pleasure to talk to you.

Wait, how do you know the sack-of-potatoes is ruled out?

kuruman's point (if I may) is that a sack of potatoes might simulate what a sinking body might do - i.e. end up in the same place. OK, nevermind the details of potatoes versus something else or weight or whatever (we could argue that forever); the kernal of kurman's idea is to simulate the accident and follow where it goes.*



Sure, it seems pretty implausible, but I gotta say, if I were a high-tech solutions finder and a sack of potatoes were my secret weapon, I might want to keep it secret too!



*Hey, they did it on CSI: Vegas once, so it's gotta be valid. Gil Grissom set up a giant swimming pool and simulated currents and wind speeds/directions to see where a drifting motor boat would end up.

 

[fresh_42]

Wait, how do you know the sack-of-potatoes is ruled out?

<censored>

You cannot achieve anything that you wouldn't already have learned from the divers because they could have acted like one.

I will request the closing of this thread before this nonsense goes on forever.

The answer, as far as it can be given, has been given: side scan sonar and calibration of echo signals by more specified equipment. Thanks @renormalize and @Dale for taking it seriously.

 

[DaveC426913]

You cannot achieve anything that you wouldn't already have learned from the divers because they could have acted like one.

Well, either you have a deeper knowledge of the circumstances than you are sharing with us, or you are thinking too inside-the-box.

It's not an outrageous idea. Simulations are a tried and true technique in all sorts of police work.

The diver's "could have" tried to simulate. Or maybe they didn't. Or maybe it just didn't lead them to the right place. None of that rules out the idea that the potato sack technique might have been the right one to produce results.

I will request the closing of this thread before this nonsense goes on forever.

I'm sorry you think it's nonsense. You asked a question because you didn't know the answer. One of our jobs is to lateralize, and think of ideas that didn't occur to you.

A shockingly low-tech solution in a sea of high tech efforts is certainly a scenario that could engender them keeping their cards close to their chest. It does fit.

The answer, as far as it can be given, has been given: side scan sonar and calibration of echo signals by more specified equipment. Thanks @renormalize and @Dale for taking it seriously.

I'm even more sorry you think people weren't taking it seriously. Pretty sure everyone was.

What I'm hearing though, is that you had a much more narrow idea of the kinds of answers you would accept than you let on.

 

[fresh_42]

I'm sorry you think it's nonsense.

Because it is for many reasons:

• sensitivity
• rocky ground (see post #1)
• density of potatoes
• range that can be examined by that method
• unknown currents
• divers, who can see more

and possibly even more. See post #6. Does that sound like potatoes?

 

[DaveC426913]

Because it is for many reasons:

• sensitivity
• density of potatoes
• range that can be examined by that method
• unknown currents
• divers, who can see more

and possibly even more. See post #6. Does that sound like potatoes?

As I said, the details can be argued forever.

You're caught up looking at potatoes, you're not seeing the forest.

The crux of kuruman's idea is to simulate what the bodies might do, and then follow them. Whatever it takes to best simulate sinking bodies.


As for the divers: it's a red herring.
Whatever they tried (and we don't know what they tried), it didn't hit paydirt.
This company with their secret technique, did.

That's all we know.

(And by the way, wet-suit-wearing, scuba-tank-sporting divers don't automatically behave like dead bodies. It may be the case that an inanimate object can be made to better simulate a dead body. Whatever. It's all still part of the same red herring. The fact is, these guys had the magic formula that did lead them to the bodies.)

 

[fresh_42]

The crux of kuruman's idea is to simulate what the bodies might do, and then follow them. Whatever it takes to best simulate sinking bodies.

Sorry, it remains nonsense, no matter how hard you try to justify that idea. It all starts with the simple observation that you don't have a well-defined starting point somewhere in the middle of a lake. This alone makes it a wet dream far from any reality.

 

[berkeman]

Thread closed temporarily for Moderation...

 

[berkeman]

their 6-year-old son fell into the water and drowned.

In most parts of the US, it is illegal for a child to be in a boat without an approved life vest. I would assume it is also true in Germany, but I don't know.

The answer, as far as it can be given, has been given: side scan sonar and calibration of echo signals by more specified equipment.

In most states in the US, drowning body search/recovery is handled by the local Fish and Game officers. On the TV documentaries that I have watched about those calls for those agencies, side scan sonar is the main tool that they use to identify potential targets for their dive teams to investigate.

@fresh_42 -- if you can contact the company to find out more about the technology, please send me a DM and we can reopen this thread with the new information you find out. Thanks.