cgull
New member
Does an altimeter on an aeroplane work in the same way as a depth sounder, ie transmit a signal to the bottom and back???
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Altimeters
- Thread starter cgull
- Start date
LadyInBed
Well-known member
No.
Altimeter works on difference in measured air pressure
Depth gauge (for Divers) works on difference in measured water pressure
Echo sounder works on difference in time between when electronic signal is sent to when the echo bounces back.
Radar works in the same manner as an Echo sounder.
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Altimeter works on difference in measured air pressure
Depth gauge (for Divers) works on difference in measured water pressure
Echo sounder works on difference in time between when electronic signal is sent to when the echo bounces back.
Radar works in the same manner as an Echo sounder.
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ccscott49
Active member
No, unless it is a radio altimeter. But they normally work on atmospheric pressure.
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ccscott49
Active member
I thought it was a sound signal, in a echo sounder? Could of course be wrong. But do radio waves pass through water?
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LadyInBed
Well-known member
It’s semantics really, a sound signal can be produced electronically.
I tend to think of a radio wave in the higher frequency spectrum, but of course it equally applies to Ultra Low Frequencies as used by Subs for comms.
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I tend to think of a radio wave in the higher frequency spectrum, but of course it equally applies to Ultra Low Frequencies as used by Subs for comms.
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Sybarite
Well-known member
There was an interesting article in Loisirs Nautiques about the use of these ultra low frequencies (ULF's) used by subs and their effect on whales. ULF's are emitted at 240 decibels and a level of 180 decibels for one minute is enough to make a man deaf. Apparently a lot of the whales die from the bends because the noise makes them shoot from the depths to the surface. This is to say nothing of the impact on their own sonar location senses.
Maritime agreements limit the use of these ULF's but once the Iraq war started, Bush exempted the subs from the restriction.
John
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Maritime agreements limit the use of these ULF's but once the Iraq war started, Bush exempted the subs from the restriction.
John
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LadyInBed
Well-known member
Yes, I heard this report on R4 a few weeks / months back. Stands to reason if anyone cares to stop and think about it.
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Evadne
Active member
Re: Whales and Sonar
Not to be confused with the ULF system used for sub communication by the US (and USSR I believe) which used radio waves, which can't deafen anyone. Radio waves only penetrate a conductor (such as the sea) as far as their "skin depth" which is proportional to their frequency.
The low-frequency sonars (sub 5kHz) that the US and other navies use vary in power, and are in the audio band used by cetaceans. The very powerful sub-hunting ones, and we're talking car-sized transducers pumping out megaWatts here, have killed pilot whales and dolphins in confined sound channels. There was a well-documented case in the Bermuda channel about 2 years ago, I don't have the url to hand but the report appeared on the NOAA website and may still be there. The world's navies are rather reticent about publicising these incidents, and you only hear about them when dead dolphins get washed ashore. I think I may have a copy tucked away somewhere if you can't find it.
On the other hand Greenpeace et. al. go for the jugular as soon as sonar is mentioned, assuming that all scientists (except theirs) are closet whale killers.
You have to be a bit careful about comparing sound in the air and the water, as the attenuation is very different, as is the energy density of identical waves. There was a proposed experiment a few years ago to transmit a sound signal across the Pacific ocean that Greenpeace very publicly opposed. They were less public when it came to admitting they'd got their sums wrong and no whales would have been invonvenienced anyway, but by then the damage had been done. But that's another story. <A target="_blank" HREF=http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v425/n6958/full/425549a_fs.html>http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v425/n6958/full/425549a_fs.html</A> has more info. and a link to the "decompression deaths" incident with the Spanish navy.
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Not to be confused with the ULF system used for sub communication by the US (and USSR I believe) which used radio waves, which can't deafen anyone. Radio waves only penetrate a conductor (such as the sea) as far as their "skin depth" which is proportional to their frequency.
The low-frequency sonars (sub 5kHz) that the US and other navies use vary in power, and are in the audio band used by cetaceans. The very powerful sub-hunting ones, and we're talking car-sized transducers pumping out megaWatts here, have killed pilot whales and dolphins in confined sound channels. There was a well-documented case in the Bermuda channel about 2 years ago, I don't have the url to hand but the report appeared on the NOAA website and may still be there. The world's navies are rather reticent about publicising these incidents, and you only hear about them when dead dolphins get washed ashore. I think I may have a copy tucked away somewhere if you can't find it.
On the other hand Greenpeace et. al. go for the jugular as soon as sonar is mentioned, assuming that all scientists (except theirs) are closet whale killers.
You have to be a bit careful about comparing sound in the air and the water, as the attenuation is very different, as is the energy density of identical waves. There was a proposed experiment a few years ago to transmit a sound signal across the Pacific ocean that Greenpeace very publicly opposed. They were less public when it came to admitting they'd got their sums wrong and no whales would have been invonvenienced anyway, but by then the damage had been done. But that's another story. <A target="_blank" HREF=http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v425/n6958/full/425549a_fs.html>http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v425/n6958/full/425549a_fs.html</A> has more info. and a link to the "decompression deaths" incident with the Spanish navy.
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Twister_Ken
Well-known member
Iraqui subs
Seems bizarre to think that George W required secure communication to submarines durine the recent 'unpleasantness' with Iraq, given that Iraq is, to all intents, a landlocked country with no navy.
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Seems bizarre to think that George W required secure communication to submarines durine the recent 'unpleasantness' with Iraq, given that Iraq is, to all intents, a landlocked country with no navy.
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Badger
Member
Iraqi Navy
Ah but they do have a navy Ken ......
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Ah but they do have a navy Ken ......
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Talbot
Active member
I beg to differ from your statement however there is only a tiny shred of truth in what you have posted. Submarines are only able to receive UltraLowFreq which is the only way to communicate with submarines underwater over long distances. There is absolutely no way that a submarine can transmit on these frequencies. The power required would give them away, and the length of the transmit wire would anchor them to the bottom!
The problem that may be confusing the whales (and has yet to be proved) is Very Low Freq active sonar to be fitted to surface ships as a means of detecting submarines at a sufficient range to be able to do something about them before the submarine can attack them. These are still at the experimental stage, and in any case would not be of any use against Iraq as they did not have any submarines!
ULF have been used for sub communications for decades with absolutely no impact on the environment.
If this is an example of the ill-informed rubbish from this magazine then I would consider cancelling any subscrioption, unless you use it cut in squares for a use more suited to its content!
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The problem that may be confusing the whales (and has yet to be proved) is Very Low Freq active sonar to be fitted to surface ships as a means of detecting submarines at a sufficient range to be able to do something about them before the submarine can attack them. These are still at the experimental stage, and in any case would not be of any use against Iraq as they did not have any submarines!
ULF have been used for sub communications for decades with absolutely no impact on the environment.
If this is an example of the ill-informed rubbish from this magazine then I would consider cancelling any subscrioption, unless you use it cut in squares for a use more suited to its content!
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penfold
Well-known member
Re: Iraqui subs
never mind that, any sub owned by them is likely to be superannuated and therefore by modern standards will be making more noise than a caribbean steel band; active sonar of any kind, let alone LF, will not be required.
cheers,
david
<hr width=100% size=1>Why'd he call me shortie?
Because you're small,...small,...S, M, all.
never mind that, any sub owned by them is likely to be superannuated and therefore by modern standards will be making more noise than a caribbean steel band; active sonar of any kind, let alone LF, will not be required.
cheers,
david
<hr width=100% size=1>Why'd he call me shortie?
Because you're small,...small,...S, M, all.
Evadne
Active member
See link in my post above. ULF sonars have killed whales and dolphins, if only in certain special circumstances. The bermuda channel incident was pretty conclusive, although the vessel in question was probably pumping out in excess of 2MW of acoustic power at close quarters to the beasts. (It's not classified, you can work it out from the figures they publish). As long as the military are reticent about these incidents, unscrupulous organisations will make capital of them for their own purposes, with little regard to telling the truth.
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starboard
Active member
Dont know if the ULF signals cause us damage but the ariel needs to be a few miles long. I understand we communicate with our subs via an ariel that is burried somewhere alog the Great Glenn in Scotland. I know for sure the Yanks hang a few miles of thiers out the back of a EC135 aircraft as it flogs around above the Atlantic ocean. As for the original question an aviation altimeter is no differant from an aneroid barometer, it is a devise that measures the rise and fall in atmosperic pressure which in turn via a sub scale is transposed into alttitude. Modern aircraft now however are also fitted with a radio altimeter that is far more accurate for flying precision approaches.Up until recent times aircraft flying below 28000ft were seperated by 1000ft for air traffic control purposes but above this by 2000ft due to the increased inacuracy with height of the aneroid altimeter. However now adays with the accurate radio altimeters this has been reduced to 1000ft for everything.
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Sybarite
Well-known member
You are correct in part. I indicated these points from memory without checking back to the article. The system is called Low Frequency Active Sonar LFAS introduced in the 80's to track the new classes of silent submarines. From surface ships.
In the article :
eg1 the coincidences of massive beachings to nearby Nato exercises and autopsies on 4 types of whales beached in the Bahamas in March 2000 portrayed evidence of auditive traumatisms (auriculaire haemorrhaging)
eg2 15 whales which had beached at Fuerteventura and Lanzarote were autopsied by Dr Jepson of the London Zoological Society and the LFAS was directly blamed as reported in the October 2003 magazine "Nature". The beaked whales presented the decompression syndrome as if... they had been chased from the bottom against their will. LFAS is still at 140 decibels 500km from its source.
In Aug 2003 a federal court judgement limited the use of LFAS in peacetime and to a zone from N. Korea to China ( sorry not Iraq) far from the coast and outside of migration periods. On the Nov 7, Bush authorised the Defense secretary to use LFAS when and where he considered necessary. A new petition has been submitted to the European Parliament and will be debated in May.
Sorry for misleading folks on questions of detail but the essence is still true. And not to blame Loisirs Nautiques which is, IMHO, a great magazine from which PBO could learn a thing or two.
John
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In the article :
eg1 the coincidences of massive beachings to nearby Nato exercises and autopsies on 4 types of whales beached in the Bahamas in March 2000 portrayed evidence of auditive traumatisms (auriculaire haemorrhaging)
eg2 15 whales which had beached at Fuerteventura and Lanzarote were autopsied by Dr Jepson of the London Zoological Society and the LFAS was directly blamed as reported in the October 2003 magazine "Nature". The beaked whales presented the decompression syndrome as if... they had been chased from the bottom against their will. LFAS is still at 140 decibels 500km from its source.
In Aug 2003 a federal court judgement limited the use of LFAS in peacetime and to a zone from N. Korea to China ( sorry not Iraq) far from the coast and outside of migration periods. On the Nov 7, Bush authorised the Defense secretary to use LFAS when and where he considered necessary. A new petition has been submitted to the European Parliament and will be debated in May.
Sorry for misleading folks on questions of detail but the essence is still true. And not to blame Loisirs Nautiques which is, IMHO, a great magazine from which PBO could learn a thing or two.
John
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Evadne
Active member
Sorry for not making it clear, the two are completely unrelated. ULF refers to the frequency only: ULF radio, as you say, is a radio transmission. ULF sonar is a sound transmission. One is a radio signal, the other we (and Flipper) can hear. It's all quite a long way from the original question.
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Talbot
Active member
Re: Submarines
Not bizarre at all, todays submarines carry Cruise missiles, and both UK and US submarines contributed to the precision attacks carried out by them.
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Not bizarre at all, todays submarines carry Cruise missiles, and both UK and US submarines contributed to the precision attacks carried out by them.
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ccscott49
Active member
Re: Whales and Sonar
Do we need this sonar? That is the question, is it worth killing any species? Do we have the right to kill these whales? I say No we dont, it is all military/government, they dont answer to anybody!
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Do we need this sonar? That is the question, is it worth killing any species? Do we have the right to kill these whales? I say No we dont, it is all military/government, they dont answer to anybody!
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Twister_Ken
Well-known member
Re: Submarines
Agreed. but for all the threat that the Iraqui navy posed to the US supersubs, George W could have sent them their orders by DHL.
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Agreed. but for all the threat that the Iraqui navy posed to the US supersubs, George W could have sent them their orders by DHL.
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