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| David Dalton |
 Posted: Fri Dec 05, 2003 1:10 pm |
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Now as long ago as ten years ago there were some protests in BC
on the effect or marine seismic airguns on marine life, and now
there is a fair bit more in Nova Scotia. So what is the
latest on the effect of such airguns on marine mammals
and perhaps even on fish and if on fish, what sort of
frequency range affects the fish most?
The question is what alternative can be come up with
to marine seismic airgun arrays.
Now on land the alternative when dynamite cannot be
used is to use an array of Vibroseis trucks with
each truck sending out a low volume but long duration
sweep waveform and when the reflected data is
cross-correlated with the sweep waveform the
resulting data is close to that of dynamite.
So perhaps the same thing can be done at sea
with a semi-submersible (submersible to avoid
too much wave action) large flat-bottomed
vessel or array of four medium sized flat-bottomed
vessels that would give off these low volume
sweeps. The coupling with the water would
not be as good as of Vibroseis trucks with
the road but would be OK, and the motion
of the water would be much lower frequency
than the sound waves and the submersion would
mean that sway from vertical would not be
too high. However that might add to the cost
of marine seismic data acquisition by a factor
of perhaps five but of course maybe less when
environmental costs are factored in.
Another thing is that I think you can use
lasers to induce sound in water so a weighted
fiber optic cable might even be able to
act as a sweep source at the bottom, not the
surface of the sea.
Those are just some brainstorming ideas I am
throwing out for discussion and may perhaps
not be practical yet but feel free to build on
them if you like (but reference this post I
guess) and to follow up if you have more
practical/constructive ideas and/or more
knowledge of recent research into alternate
marine seismic sources and/or the effect of
marine seismic activity on marine life.
David (geophysicist but more applied math than practical) |
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| David Dalton |
| Posted: Fri Dec 05, 2003 2:12 pm |
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David Dalton wrote:
Quote: Another thing is that I think you can use
lasers to induce sound in water so a weighted
fiber optic cable might even be able to
act as a sweep source at the bottom, not the
surface of the sea.
Actually when I thought of that I was thinking of
sonoluminescence which however is the production of light
by sound passing through a liquid, not the reverse, but
I still think the reverse, so laser stimulation of
sound in water, is also possible but won't crosspost
this to the optics and main physics newsgroups.
I'll see if I can brainstorm some more ideas about
this in the next while, perhaps involving EM to
acoustic conversion in a layer so that layer can
act as a near plane wave low volume sweep source
though of course in such a case the coupling
would be such that the EM energy would be a fair
bit higher than the resultant acoustic energy
and may itself have negative effect on marine life.
But that is just a quick last minute idea that
if I contemplated for a few minutes might decide
it is not at all feasible even if I was Tesla
or Jim Wait. :-)
David
http://www.nfld.com/~dalton (CV, abstracts, music stuff, mystic BS) |
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| Peter Larsen |
| Posted: Fri Dec 05, 2003 6:22 pm |
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David Dalton wrote:
Quote: Now as long ago as ten years ago there were some protests in BC
on the effect or marine seismic airguns on marine life, and now
there is a fair bit more in Nova Scotia.
About time. The planets oceans are full of life that uses audio for
orientation and navigation. Simple common sense should dictate that we
try to avoid making unnecessary noise in the sea. Hearing damage is
considered as being one possible explanation of the beached cetacean
problem.
I think we should look into using something other than sound for
charting the seas, the current scientific noise pollution is as
defendable as "scientific whaling" (presumeably done to verify that the
cooking time for whale meat is unchanged!).
Quote: David (geophysicist but more applied math than practical)
Kind regards
Peter Larsen
--
*************************************************************
* My site is at: http://www.muyiovatki.dk *
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| David Dalton |
| Posted: Sat Dec 06, 2003 11:45 am |
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David Dalton <dalton@nfld.com> wrote:
Quote: Now as long ago as ten years ago there were some protests in BC
on the effect or marine seismic airguns on marine life, and now
there is a fair bit more in Nova Scotia. So what is the
latest on the effect of such airguns on marine mammals
and perhaps even on fish and if on fish, what sort of
frequency range affects the fish most?
The question is what alternative can be come up with
to marine seismic airgun arrays.
Now on land the alternative when dynamite cannot be
used is to use an array of Vibroseis trucks with
each truck sending out a low volume but long duration
sweep waveform and when the reflected data is
cross-correlated with the sweep waveform the
resulting data is close to that of dynamite.
So perhaps the same thing can be done at sea
with a semi-submersible (submersible to avoid
too much wave action) large flat-bottomed
vessel or array of four medium sized flat-bottomed
vessels that would give off these low volume
sweeps. The coupling with the water would
not be as good as of Vibroseis trucks with
the road but would be OK, and the motion
of the water would be much lower frequency
than the sound waves and the submersion would
mean that sway from vertical would not be
too high. However that might add to the cost
of marine seismic data acquisition by a factor
of perhaps five but of course maybe less when
environmental costs are factored in.
Now if famous elder geophysicist Klaus Helbig had still
been visiting Newfoundland (he likes it here and will be
back in 2004) and at the desk next to me still I would have
floated such ideas off of him and he would have said impractical,
probably, but at least I am trying to start discussion.
Two more ideas I had last night were on:
1. Directivity
Now simplistically for a 2-D seismic survey you might think
you need mostly in-plane energy and almost vertical energy.
But in practice though seismic data is processed to simulate
vertical incidence it is most commonly recorded on a wide
spread of hydrophones around the sourcs and also in areas
of complex geology for a 2-D survey there can be out-of-plane
reflections. Moreover for the now-common 3-D marine survey
there can be a wide 3-D aperture needed around the source.
Still, even if that is a wide cone it is still less than
the full halfspace and would not travel as far sideways
directly though of course there would be multiple reflections
in the water layer. So ideally a marine seismic source
could resrict energy to that wide cone. However an airgun
injects a very high pressure bubble into the water and
is not very directional (I think) and I doubt it is possible
to fit it with an acoustic analogue to a parabolic reflector.
So maybe some research should be done into more directional
sources.
2. migration tracking
Modern marine biologists and fisher elders do a fair amount of
tracking of marine mammal migration patterns and fish stock
migration patterns so it should be possible to predict such
migrations to some extent and schedule surveys so as to not
interfere with such migration patterns. This would just be
one added factor along with weather, sometimes ice, and
ship availability, to weigh into consideration.
OK, those are my points for today and if any more come
to me tonight I will follow up again tomorrow briefly.
David |
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| Daryl Krupa |
| Posted: Sun Dec 07, 2003 12:03 am |
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David Dalton <dalton@nfld.com> wrote in message news:<bqqido$s69$1@coranto.ucs.mun.ca>...
<snip>
Quote: The question is what alternative can be come up with
to marine seismic airgun arrays.
Now on land the alternative when dynamite cannot be
used is to use an array of Vibroseis trucks with
each truck sending out a low volume but long duration
sweep waveform and when the reflected data is
cross-correlated with the sweep waveform the
resulting data is close to that of dynamite.
So perhaps the same thing can be done at sea
with a semi-submersible (submersible to avoid
too much wave action) large flat-bottomed
vessel or array of four medium sized flat-bottomed
vessels that would give off these low volume
sweeps. The coupling with the water would
not be as good as of Vibroseis trucks with
the road but would be OK, and the motion
of the water would be much lower frequency
than the sound waves and the submersion would
mean that sway from vertical would not be
too high. However that might add to the cost
of marine seismic data acquisition by a factor
of perhaps five but of course maybe less when
environmental costs are factored in.
snip
David:
The sea bottom is usually floored with such thick unconsolidated
materials.
If you had a sunken barge bouncing up and down, low-rider-like,
on the sea floor, you might get a fair amount of information, but a
thumper truck would likely punch a hole through the floor of the
barge, unless it was steel of a significant thickness, in which case
the signal gets diffused somewhat, no?
And thumping on a floating barge would send shivers along my spine;
that had better be an unmanned ship, due to the effect such activities
would have on the spine and belly of the ship.
Maybe you should count on using say, five ships in succession until
your seismic program was completed.
"Let me see if I have this aright, matey:
you want to put a giant hammer aboard my ship and
bang it up and down until the sea boils around it?
I may be a poor, unemployable former cod fisherman,
but I'm not ready to die yet. Off with you now, and
ask Lloyd's of London what they think of yer scheme there bye."
Solely in jest,
Daryl Krupa |
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| David Dalton |
| Posted: Sun Dec 07, 2003 2:33 pm |
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Daryl Krupa wrote:
Quote: The sea bottom is usually floored with such thick unconsolidated
materials.
If you had a sunken barge bouncing up and down, low-rider-like,
on the sea floor, you might get a fair amount of information, but a
thumper truck would likely punch a hole through the floor of the
barge, unless it was steel of a significant thickness, in which case
the signal gets diffused somewhat, no?
And thumping on a floating barge would send shivers along my spine;
that had better be an unmanned ship, due to the effect such activities
would have on the spine and belly of the ship.
Maybe you should count on using say, five ships in succession until
your seismic program was completed.
No, I want the entire bottom of the barge to vibrate, not to
have a thumper truck inside a barge. I'm not sure if the
submersion is needed at all but in any case I did not mean
submersion as far as the sea floor but just a bit below
surface so a flat-bottomed barge (well to submerge it would
need walls of some kind though) would be more stable
but again such submersion may not be needed and indeed
a flat bottom might not be needed but the outer hull of
a double hulled ship at least in its part below water
could sweep vibrate and act as an acoustic antenna/source.
The large surface area of such a hull (or barge flat bottom)
would mean that the vibration would not have to be as
intense as on the small surface area of a Vibroseis (thumper)
truck base plate. Also surely engineers reading can build
on my comments and design something practical and stable
(a giant phallic vibrator sub  ).
David |
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| Pyats |
| Posted: Sun Dec 07, 2003 3:33 pm |
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David Dalton wrote:
Quote: No, I want the entire bottom of the barge to vibrate, not to
have a thumper truck inside a barge.
How would that save the whales? |
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| David Dalton |
| Posted: Sun Dec 07, 2003 7:36 pm |
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Pyats wrote:
Quote: David Dalton wrote:
No, I want the entire bottom of the barge to vibrate, not to
have a thumper truck inside a barge.
How would that save the whales?
You mustn't have read my initial post. Vibroseis works with
a long low volume sweep not an extremely high volume short
explosion (or in the case of airguns injection of a very
high pressure bubble of air very quickly). So that low
volume long sweep would be much easier on the whales ears
than the very high volume airgun explosion. But it remains
to be seen if such a vibrating barge bottom or hull can
be designed and even if so it will take a while and in the
short term adjusting marine seismic schedules if possible
to account for marine life migration patterns should be
considered. I know, the whales might prefer a total
ban on marine seismic, but I went for the compromise.
But you know, the oil industry might be still
using dynamite in populated areas if they could but
only switched to Vibroseis because they had to
at first at least but since may have found the
Vibroseis setup has some advantages when there
are roadways for access (plus traffic noise
when cross-correlated with the sweep sort of
goes away but would be present in dynamite data).
Hmmm, maybe I should have just studied more of
Sheriff and Geldart second edition as I was supposed
to last week (but a different chapter) or floated
my ideas by Chuck Hurich, Jeremy Hall, Jim Wright
and even my supervisor Michael Slawinski (plus
gotten Klaus Helbig's e-mail from him) before
posting them here. But I am always in a rush
and more ready to stick my neck out and play the
brainstormer/fool a bit on newsgroups than off.
Also of course local Newfoundland groups
PEGN, NATI, NOIA, NEIA, and MUN (including Genesis
centre) might be interested but perhaps not
and I think the Genesis people want you to work up
your idea whereas I like to crank (in more ways
than one) them out and get on to the next one, just
in my spare time, and if some catch on can always
do some brainstorming/idea percolation consulting eventually.
David |
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| Angelo Campanella |
| Posted: Mon Dec 08, 2003 7:51 am |
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Daryl Krupa wrote:
Quote: The question is what alternative can be come up with
to marine seismic airgun arrays.
Now on land the alternative when dynamite cannot be
used is to use an array of Vibroseis trucks with
each truck sending out a low volume but long duration
sweep waveform and when the reflected data is
cross-correlated with the sweep waveform the
Is this not what we call MLSA? If so then where is the trade-off of time
vs intensity falling short of satisfying your needs? Give us some
numbers, please.
Angelo Campanella |
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| David Dalton |
| Posted: Mon Dec 08, 2003 7:06 pm |
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Angelo Campanella wrote:
Quote: Daryl Krupa wrote:
(actually I, David Dalton, wrote the next bit and Daryl
was quoting it)
Quote: The question is what alternative can be come up with
to marine seismic airgun arrays.
Now on land the alternative when dynamite cannot be
used is to use an array of Vibroseis trucks with
each truck sending out a low volume but long duration
sweep waveform and when the reflected data is
cross-correlated with the sweep waveform the
Is this not what we call MLSA?
What does MLSA stand for (of course if it is a geophysical
term I will look out of touch but I haven't been to
an SEG conference since 1990 in San Francisco)?
Quote: If so then where is the trade-off of time
vs intensity falling short of satisfying your needs? Give us some
numbers, please.
Well, the supposed problem is that short pulse but high
intensity airgun pulses may be too hard on some marine
organisms though that is still subject to research, so
I suggested maybe a string of towed vibrating submersibles,
whether flat-bottomed of not, towed behind a big ship
perhaps, sending out a long low amplitude sweep similar
to Vibroseis truck sweeps. So I guess the only problem
is in designing the appropriate technology, and perhaps
those with more practical experience in the field will
comment on the numbers further. But ideally each
towed submersible vibrating (as a whole, like a
personal massage unit in the tub) unit maybe would
be about the size of a life raft or something, so
probably engineering students could design it as
a course assignment or something, given needed time
and intensity and directionality specs I guess.
Some engineers of sci.engr may be following this thread
and if there is any environmental group pressure on
government(s) and government(s) pressure on oil companies
and contractors there probably already is some behind
the scenes consideration of alternatives going on.
David |
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| Daryl Krupa |
| Posted: Mon Dec 08, 2003 11:26 pm |
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David Dalton <dalton@nfld.com> wrote in message news:<br000f$gm0$1@coranto.ucs.mun.ca>...
<snip description of something out of "Flesh Gordon">
David:
Have you considered posting your idea to
sci.geo.oceanography?
Also, would you not get a better signal using a
parabolic dish, or a megaphone trumpet?
(The latter, and the vibrator analogue, might fit in with
a ship named "Rudy Vallee".)
Then again, why not just cut out a portion of the hull and replace
it with a diaphragm? And hit it with repetitive piston action? That
should get you onto the evening news ...
Daryl Krupa |
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| Angelo Campanella |
| Posted: Tue Dec 09, 2003 11:06 pm |
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David Dalton wrote:
Quote: What does MLSA stand for (of course if it is a geophysical
term I will look out of touch but I haven't been to
an SEG conference since 1990 in San Francisco)?
"Multiple Length Sequence (analysis?)"
Basically instead of one big boom, the sound (or vibration) is
generated at a continuous low level, being modulated in a very special
and phase coherent way. (A series of pulses or aqaure waves cued in a
specail and detern=ministic fashion, which "sequency", lasting a minute
or more before it needs to be repeated, can be repeated indefinitely,
the result being averaged ("integrated") for more precision or
resolution. The received signal is alayzed with a demodulator driven by
exactly the same signal so that a long coherent result occurs.
In the case of measuring auditorium reverberation time, instead of one
big BANG!, the emitted signal is a hushed steady random noise that may
last up to a few minutes. It can be done while folks are millinmg around
and talking. The result occurs with persons barely noticing. I think the
marine animals would be rather pleased.
Angelo Campanella |
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| Tony |
| Posted: Wed Dec 10, 2003 4:45 am |
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"Angelo Campanella" <a.campanella@att.net> wrote in message
news:rZwBb.425557$0v4.20425217@bgtnsc04-news.ops.worldnet.att.net...
Quote: "Multiple Length Sequence (analysis?)"
Basically instead of one big boom, the sound (or vibration) is
generated at a continuous low level, being modulated in a very special
and phase coherent way. ...(snip).
.... It can be done while folks are millinmg around
and talking. The result occurs with persons barely noticing. I think the
marine animals would be rather pleased.
Seems like a good idea but just watch that the path conditions are constant
during the measurement. It's great if you can manage with a 10 minute test
but if not, the time escalates very rapidly. Theory says you get 3 dB more
signal to noise ratio from doubling the duration, so from 10 minutes, to get
another 6 dB you have to go to 40 minutes. I would guess that this might be
a problem with long ocean paths due to currents moving water at different
temperatures around. If you're actually trying to track things that change
it's hopeless.
Tony Woolf |
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| David Dalton |
| Posted: Wed Dec 10, 2003 4:35 pm |
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Daryl Krupa wrote:
Quote: David:
Have you considered posting your idea to
sci.geo.oceanography?
I posted a pointer there, "whale hearing and airguns"
referring to this thread, so I imagine if any were
really interested they would have looked here.
Hmmm, I have Jon Lien's e-mail address from a
few years ago somewhere (Michael Rochester gave
it to me) and if it is still the same may
e-mail him in the new year with all of my
past whale-related ideas and any new ones
that I think of while compiling them. He
heads a local group that rescues a lot of
whales from fishing gear, here in Newfoundland.
David |
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| David Dalton |
| Posted: Wed Dec 10, 2003 4:42 pm |
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Tony wrote:
Quote: "Angelo Campanella" <a.campanella@att.net> wrote in message
news:rZwBb.425557$0v4.20425217@bgtnsc04-news.ops.worldnet.att.net...
"Multiple Length Sequence (analysis?)"
Basically instead of one big boom, the sound (or vibration) is
generated at a continuous low level, being modulated in a very special
and phase coherent way. ...(snip).
.... It can be done while folks are millinmg around
and talking. The result occurs with persons barely noticing. I think the
marine animals would be rather pleased.
Seems like a good idea but just watch that the path conditions are
constant
during the measurement. It's great if you can manage with a 10 minute
test
but if not, the time escalates very rapidly. Theory says you get 3 dB
more signal to noise ratio from doubling the duration, so from 10 minutes,
to get
another 6 dB you have to go to 40 minutes. I would guess that this might
be a problem with long ocean paths due to currents moving water at
different
temperatures around. If you're actually trying to track things that
change it's hopeless.
Well, in this case you are trying to measure what's in
the solid rock under the ocean layer, and that doesn't
move around, so it shouldn't be a problem, unlike
long path ocean acoustics. The density and velocity
variations between rock layers can be much greater than
the time-variant small variations in the ocean layer.
David |
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