Twenty passengers on missing flight 370 worked for Freescale Semiconductors

[pickle9000]

My understanding is this.

When they are at the range limit of the pinger, everything is hard, there are reflections, shadows background noise. As they get closer these are less of an issue. It's important to get as much acoustical data as possible so that if the pinger does fail they will still have a good chance of locating the wreck. The next stage will be a sidescan sonar.

I think if they get another 5 days of pinger activity they could well be grabbing the first flight recorder.

I assume (because of the lack of debris) there are going to be some really big sections.

[mikeselectricstuff]

Considering the relatively slow propagation speed, I'd have thought it would be pretty feasible to get a more accurate location using multiple hydrophones with precise timing, just like GPS.
 

[pickle9000]

There is a British sub on site, I think subs use multiple hydrophones for that purpose. 

[CaptnYellowShirt]

Considering the relatively slow propagation speed, I'd have thought it would be pretty feasible to get a more accurate location using multiple hydrophones with precise timing, just like GPS.
 

If only the forum had an expert on this subject ... 

[johansen]

well, it did, not but a few wanted to hear any of it.

[cimmo]

Random semi-related question - when there's a high-profile crash, do they change the flight number for future schedules?
( I was actually  on the previous week's AF447 )

The MH370 route is now known as MH318.

http://worldairlinenews.com/2014/03/13/malaysia-airlines-retires-mh-370-and-mh-371-flight-numbers-9m-mro-may-have-flown-for-four-hours-after-losing-contact-no-debris-found/

FWIW, the AF447 route was renamed as AF445 and there was an incident on this same route that freaked a few people not long after the AF447 incident:
http://avherald.com/h?article=42380873

[EEVblog]

There is a British sub on site, I think subs use multiple hydrophones for that purpose.

Subs with use either a towed array and/or a hull based array strip.

[EEVblog]

Considering the relatively slow propagation speed, I'd have thought it would be pretty feasible to get a more accurate location using multiple hydrophones with precise timing, just like GPS.

Yes, and that is why sonobuoys are dropped in groups, usually not on their own.
A typical sonobuoy will have an array of sensors, in the case of the one I worked on, 5 arms with 5 sensors each, a few meters long.
http://www.engineeringicons.org.au/engineering-icons/australian/barra-sonobuoy-system/ImagesVideosAudio/design.pdf
Each one has an accurate digital compass that knows which way the arms are pointed.
If you only have one sonobuoy then target positional accuracy is not that great, that's why they almost always drop more than one.
And BTW, they work for 4 hours and then automatically sink themselves to the bottom. $5K a pop, likely more these days.

[pickle9000]

These are the submersible items at the search location that I know of.

- HMS Tireless is the sub from the UK it does have a towed array and hull mounted flank array sonar. The sub is 85 meters long.
- The towed "black box detector" is currently running a grid pattern over the suspected area.
- The Bluefin 21 is loaded with a side scanning sonar.

There is no word of an ROV capable of picking up the flight recorders but that must be in the works. I would think the sooner the better (cost wise).

[EEVblog]

Why do they need to sink? Can't they be retrieved and recharged? $5K seems a bit borderline for being disposable.  Perhaps I am wrong in assuming they are deployed from a boat.

Sorry, I forgot to mention these are military sonobuoys. They can be dropped some planes, helicopters, or ship decks. They would automatically scuttle themselves to the bottom so that the "fishing trawlers" from *insert current enemy country* (Russia during the cold war these were developed and speced) couldn't come along and pick them up. Once they have one, they can determine the capabilities and how well they can detect their submarines. So the ocean floor is lettered with these things. I'm sure most countries militaries would have this same policy too.
The alternative is towed array sonars they would winch out behind behind ships or submarines. But by the time you have detected a sub using one of those, it's probably close enough to blow you out of the water.

[CaptnYellowShirt]

They would automatically scuttle themselves to the bottom so that the "fishing trawlers" from *insert current enemy country* (Russia during the cold war these were developed and speced) couldn't come along and pick them up.

Does the pressure typically kill them?

[SeanB]

They would automatically scuttle themselves to the bottom so that the "fishing trawlers" from *insert current enemy country* (Russia during the cold war these were developed and speced) couldn't come along and pick them up.

Does the pressure typically kill them?

Pressure will collapse any sealed voids, but they rely on it being a big ocean and a really small target. think of trying to find the plane and not having a pinger giving data to narrow the search area, and then think of searching the entire ocean bottom looking for a submerged object the size of an office chair, with a whole lot of other litter and rock there as well.

[pickle9000]

They would automatically scuttle themselves to the bottom so that the "fishing trawlers" from *insert current enemy country* (Russia during the cold war these were developed and speced) couldn't come along and pick them up.

Does the pressure typically kill them?

Pressure will collapse any sealed voids, but they rely on it being a big ocean and a really small target. think of trying to find the plane and not having a pinger giving data to narrow the search area, and then think of searching the entire ocean bottom looking for a submerged object the size of an office chair, with a whole lot of other litter and rock there as well.

Tamper protection for sure, at least no power no software.

[SeanB]

As these are likely supplied with a battery soldered in ( or otherwise not removeable without opening sealed covers) then that will work. Then they have a shelf life and are not store and forget until needed then pop in a pair of D cell units.

Missiles were a lot easier, no battery, firmware stored in ROM and a 90 second after firing self destruct. Power supplied by the aircraft bus when on the wing, and in flight by a small gas generator that did double duty as sensor cooling.

[EEVblog]

Does the pressure typically kill them?

Very likely, they are only designed for 50m or so, and for only 10 hours maximum. The bungie cord dangles the sensor array about 30m under the water.

[EEVblog]

As these are likely supplied with a battery soldered in ( or otherwise not removeable without opening sealed covers) then that will work. Then they have a shelf life and are not store and forget until needed then pop in a pair of D cell units.

Yep, a really custom expensive lithium primary battery is soldered in place.
Our commercial seismic ocean bottom used rechargable battery packs and were recovered to extract the data, charged, ad then redeployed. They were designed to  operated at several thousands meters depth for up to several months, continually logging data.

[pickle9000]

The latest, even on topic.

"On Wednesday, Australia sent a P-3 Orion military aircraft to drop 84 sonar buoys in a remote patch of the southern Indian Ocean, broadly in the same spot where the Australian defense vessel Ocean Shield detected the stream of signals. Each sonar buoy is equipped with a set of underwater microphones that unspool on wires to a depth of 1,000 feet."

[pickle9000]

So here is the updated handout. The green circle is my guess. I figure they are trying to follow a strong signal but there is a "shadow" blocking the signal. Of course I could be completely wrong.

[EEVblog]

So here is the updated handout. The green circle is my guess. I figure they are trying to follow a strong signal but there is a "shadow" blocking the signal. Of course I could be completely wrong.

The correlation with (one of) the satellite handshake arc is impressive.

[EEVblog]

Each sonar buoy is equipped with a set of underwater microphones that unspool on wires to a depth of 1,000 feet."

Either my memory is shot and the 30m was actually 300m, or they have a new model since the 6PC (6th Production Contract) one I worked on. Or the report is wrong and it's 100ft. IIRC the production contract was 15,000 units.

[pickle9000]

Each sonar buoy is equipped with a set of underwater microphones that unspool on wires to a depth of 1,000 feet."

Either my memory is shot and the 30m was actually 300m, or they have a new model since the 6PC (6th Production Contract) one I worked on. Or the report is wrong and it's 100ft. IIRC the production contract was 15,000 units.

- 60 feet is generally considered to be the upper ocean layer so 30m / 100 feet seems more reasonable.
- The satellite guys did an amazing job both with the idea and execution.

[firewalker]

Either my memory is shot and the 30m was actually 300m, or they have a new model since the 6PC (6th Production Contract) one I worked on. Or the report is wrong and it's 100ft. IIRC the production contract was 15,000 units.

After deploy of the units is it necessary to collect it? Is it reusable? Is there an ad-hock network between the units?

Alexander.

[EEVblog]

After deploy of the units is it necessary to collect it? Is it reusable?

No, they are single use disposable. A little resistor in the float bag burns after 4 or 8 hours (selectable) and the whole thing sinks to the bottom.

Is there an ad-hock network between the units?

No, they do not receive any information, they only continually transmit the hydrophone data and compass heading. Not even GPS to know their position, they just tag that when they drop them and they rely on the currents not drifting much of significance within the operational time.

[firewalker]

I guess the sink is a measure to avoid any encounter with ships and marine life (sharks etc).

Alexander.

[Kjelt]

$5k a piece sounds like a lot of money untill you know what ammunition costs esp. the larger shells.
When I was in the army in the 1980's the dragons (anti tank missiles) were already costing $10k a piece and for practice those guys shot around 5 pieces a person (6 persons) in a weekend, and that was just the yearly training. Add tankshells, mortars hell laserguidedmissiles and $5k is peanuts.