from: not yet published :-)
Meteor Perception Sounds
The abilities of video systems like our MOVIE
has been discussed already in detail, they provide us with very accurate optical
information on what is going on in the sky. Nevertheless, other important
types of data have been completely ignored so far. Thus, the aim of
this work is to show the chance of getting valuable acoustic information
from video recordings.
Normally meteor astronomers observe together in groups. Watching the sky alone
with usually almost no meteor activity is boring but if you have a partner
you can at least share your annoyance about the situation with him. In addition you
have the happy moments when the other saw a nice shooting star whereas you did not
concentrate on the sky for a second.
In the last few years I often observed together with DUBKA and NITMI. In those nights I found out
that it is possible to guess the brightness of a meteor I have not seen accurately from the sound
the other observers make: A little 'Huch!' is not so bad - I only missed an
unimpressive +3 mag or even +4 mag meteor whereas an 'Oi!' or 'Wow!'
follows a meteors of about 1 mag. If I hear a most excited 'Waaaahnsinn!!!' or
any other undefined phonemes that does not correspond to proper German words I can be quite
sure that something really bright appeared and I did not see it.
What has that to do with MOVIE? You may know that the recording part
of our video system is not a video camera but a Camcorder which, as all devices
with this name, has a microphone, too. Thus, many of the human meteor perception sounds
are recorded and I can adjust my brightness estimation scale even better by
analysing these video tapes. Even more there is valuable information about meteors
outside the cameras field of view and about meteor properties the system cannot record.
Unfortunately there is always a lot of background noise (for example from our power generator
and the mounting) and the observers are far away from the video system, still many
of the sounds are clearly understandable.
In a first approach to the problem I've tried to classify the sounds. For that
I have browsed through our tapes starting from the Quadrantids '93 up to the Lyrids
from '95. There have been about 200 meteors included in this investigation, in 29 cases I found
a distinct sound coming from one or many observers noticing the event.
Five of them had to be be rejected later because their SNR was too bad, so I could not
classify them. The others fit neatly into one of the following four classes:
- faint meteors: Perception sounds following faint meteors are characterised by a
great variety of words or phonemes that are used. They are normally very short and not very loud.
Whereas our female observer tends to react most often with 'Huch!', we
get more variable responses like 'Oi!' and
'Ou!' by male observers.
It could be shown that different observers say different words after watching the same meteor: In the
following example we can hear 'Eij!', 'Ja!' and 'Schön!'
at the same time. This makes the acuostic analysis more complicated, but I hope to
come up with a list of equivalent words later. Furthermore we should not forget that
visual brightness estimations are often not consistent, too.
Another problem are words and sounds that cannot be written because they just do not
exist: Maybe we are dealing here with a mix of two common sounds or
the observers has just no time to respond due to high activity.
- bright meteors: If an observer notices a brighter meteor he has generally more
emphasis in his voice. The classification of meteors that are just inbetween faint and bright
is sometimes not easy, because the used words are still the same. Anyway, an experienced listener
can conclude from the pronounciation of the phrase 'Oi!' alone
that the observer just saw a +1,5 mag or +2 mag, hence, a bright meteor. He concentrates
completely on the event because he knows that it has been the last bright shooting star for a
Once the meteor becomes even brighter it is easier to classify, because the reactions
of the observers change dramatically: They use more and longer words and they tend to
'motivate' the meteor shower with positive attributes. In a typical case you may hear
'Oh! ... Wahnsinn!' and 'Gut!' as a try to
stimulate even more events of that type.
There is a trend that male observers show more emotions at this stadium, they say
'Da! ... Oi! ... Cool!' compared to 'Wahnsinn! .. Oah!'. Even words
like 'Boah!' may be heard in such a situation.
- fireballs: Especially thrilling are, of course, meteors brighter than -3 mag. We
call them fireballs from their visual appearance, but what about the acoustic responses?
First of all we can classify all sound events that last longer than
three seconds to be triggered by fireballs. In the standard case we hear common
sounds like 'Oh!' and 'Wahnsinn!' with an
intensity and volume that might even wake up sleeping meteor observers from
their sweet dreams. If they are lucky enough they might still see the dimishing persistent train
of the bolide, if not there is hope for another effect:
Highly trained observers tend
to give away valuable information about the color (blue) and unexpected
things like distortions of the train due to winds in the higher
atmosphere. Even though this makes fireball perception sounds most significant and important
in acoustic meteor observation we also have to consider certain dangers. It could be shown
that too bright and slow meteors may result in ecstatic observer states causing an exponential voice
volume increase. This is to blame for serious damages of the hearing system of
other nearby observers!
- special events: Perception sounds have to be classified as special events if
the observer was not in the standard observing position or mood.
Finally we have to consider different languages and the strange reactions of non meteor observers.
Whereas a Dutch observer can be regarded as a good classifier for
meteor parameters, too, we have to be careful with unexperienced people:
- There are the so called pre-observation meteors that occur during the system
setup. Their perception is characterized by ignorance, the observer notices the event
but goes on to work without interruption (unless the meteor did belong to the class fireball). This might result
in simple expression sentences like 'There was a shooting star!'.
- During the observation the camera operator has to change the field of view and
control the recording system sometimes. Probability theory and Murphy's law demand
a significant increase in meteor activity at those times because both the camera and the observer
are not active. Thus, the operator notices regularly meteors at the control monitor and his unhappyness
triggers a demotivated sentence.
It is most interesting that the used words in this situation are always the same which makes
it a good indicator for the overall psychological condition of the observer. In addition
it is a good test for visual perception abilities of non meteor observers who tend to react
to the announced meteor with the question 'Where?'.
- After a long night with hundreds of meteors even the hardest observer becomes
tired and cannot react appropriately anymore to bright meteors or
even fireballs. This is the recommended time to stop acoustic analysis to avoid major errors.
- Once the observer has finished the active work he just cannot relax but stands in front of
the still working video monitor and realizes that the real show is just starting. It is not uncommon
that he or she can count in real time more meteors per minute than
in the whole last hour.
- Some of them try to do their best to copy the professionals, but they simply do not know
standard reactions and use wrong phrases.
- Others are completely overwhelmed when they see a meteor of
the class 'bright' and respond as if one had to expect a nearby impact soon.
- Finally there are human beeings who have never seen a meteor before. Depending on their
age and sex they respond completely chaotic and non-predictable, hence,
they should be left out in any serious investigation.
I want to conclude that acoustic recordings of meteor observations contain valuable data
about meteor brightness, frequency and specific properties. The next step should be the
standardization of perception sounds using a describtive sound cataloge to make the reactions
even more reliable. Maybe we should generally react in English to make results from all over
the world comparable.
The introduction of a normalized AHR (acoustic hourly rate) is an open problem, too.
Sirko Molau; last change: October 19, 1995