[Prev][Next][Index][Thread]

(meteorobs) Visual Observations of Meteor Storms

Even though it is still the basic meteor observation technique, visual 
observation has a number of disadvantages and limitations. One of the 
limitations became obvious during the spectacular Leonid meteor storm of 
1966. When the number of meteors exceeded several shooting stars per 
second, human observers were not able anymore to follow the activity 
with the standard observing techniques.

In 1966, the observers switched to a different method near the time of 
maximum of the Leonid storm. They did not count the individual meteors 
anymore, but opened their eyes for only a second and tried to estimate 
the numbers of meteors at this moment. Until now it is not perfectly 
clear, in how far this change of technique influenced the rates derived 
from the observations afterwards (EZHR>100.000). A recent A&A paper of 
Peter Jenniskens suggested, for example, that the activity may have been 
overestimated by an order of magnitude. There was an argument in recent 
WGN issues, whether human observers are able to give precise activity 
estimates at all, when the equivalent ZHR becomes bigger than 10.000.

So, one of the main scientific goal for the possible return of the storm in 
1998 is to calibrate the old observations with new data. The idea is to use 
the same observing techniques as in 1966, but operate video systems in 
parallel to have the 'ground truth'. If the rates will be high enough we 
may find out, whether visual estimates under these conditions are 
systematically in error, and if they are reliable at all.

In Germany, a group of about 15 observers is preparing for an expedition 
to Mongolia. In one of the preparation meetings the idea was born, to 
write a computer simulation of a meteor storm. This may give us a first 
clue, what to expect and how the chances for accurate visual observations 
are. In addition, different visual methods may be tested in advance to find 
out, which observing technique is most appropriate for observations under 
very high activity.

We started with a simple program of H. Luethen. It displayed an arbitrary 
number of lines for just one second, similar to the 1966 observing 
technique. Later the estimates were compared with the true number of 
lines displayed. The tests have been repeatedly carried out by different 
German observers in the last few weeks. The results were promising - 
usually the relative error was not larger than about 25%. A detailed 
analysis will be published in WGN later on.

The major drawback of this first simulation was, that it had only little in 
common with reality. It was a good test, whether humans are able to 
estimate a larger number of objects at one instance, but under clear skies 
the job is much more difficult.

This is why I decided to develop an improved simulation. Now, meteors 
are not anymore simple lines, but elongated moving objects. They do have 
different brightnesses, light curves, velocities, directions, persistent trains, 
etc. as in reality. Furthermore, the sequence of shooting stars is computed 
with an exponential distribution. Thus, the often reported 'cluster effects' 
become clearly visible. A number of background stars helps to improve 
the display.

To run the program, a fast PC / graphics card is necessary. The simulation 
should be executed under DOS. 
The software is available via anonymous from IMO’s ftp server at 
ftp.imodot net, directory /pub/software/metsim, or via our WWW homepage at 
http://www.imodot net/visual/major03.html.

Please, send your questions, data files, suggestions for improvements, and 
other comments to the author (molau@informatik.rwth-aachendot de).

Enjoy the simulation!
Sirko Molau

----------------------------------------
Sirko Molau -- Video Commission Director
International Meteor Organization
e-mail: video@imodot net
WWW   : http://www.imodot net/video
----------------------------------------