(meteorobs) Determining meteor speeds with all-sky cam?

[Esko Lyytinen]

If one gets measured good individual directions for each video frame, 
then the change of the apparent angular velocity tells the true 
direction of entry. And with reasonable begining height one can "scale" 
the whole entry path with velocities also. The beginning height depends 
also on the velocity but with an iteration a reasonable value can be 
obtained. The atmospheric deceleration also affects the apparent angular 
velocity, but this mainly affects the end part of the track and less so 
the beginning part (which, because of this, is more important for this 
derivation). Only if a relatively long apparent (angular) track on the 
sky is visible, can you expect to get a good result.

I have derived like this, a good number of meteor entry tracks including 
velocities. Some of these could later be determined from multistation data.
In good instances the accuracy of the entry direction may be around two 
degrees or better. And the accuracy of the velocity about or better than 
10%.
The latest such derivation was the 2011 May 13/14 in British Columbia
http://lunarmeteoritehunters.blogspot.com/2011/05/montana-washington-idaho-alberta.html
In this case the original direction (by means of the Cranbrook video) 
from az. 17 altitude 39 degrees, did not change (by good luck) even a 
degree after two other videos came available. ( now 17.0 , +39.4 )
The beginning height and consequently the velocity did increase a 
little. The veloctiy is now 24.5 km/s, as compared to that 22 km/s what 
is mentioned at that lunarmeteoritehunters blog.
( This entry is still not especially well determined, because of non 
good mutal situation of the camera stations relative to the meteoroid 
track (and the two others at bigger distance), but probabaly within 
about a degree accuracy, as to the direction.)

High velocity meteors are less affected by atmospheric deceleration and 
because of this (if of enough apparent angular length) are more suitable 
for this, but this can be applied also for meteorite droppers, as for 
example that British Columbia example shows. Then a deceleration model 
also for the beginning part is very valuable. The end may tell something 
of the deceleration, and a physical ablation model can continue from 
this. And some iteration between these can be further applied.

In some instances, a rough one station value of velocity can be got even 
without accurate frame data. For example if it is apparently close to a 
point meteor and so coming towards the observer, then (considering also 
the apparent visible altitude angle (of the point meteor) and reasonable 
beginning height) the path length must be limited (between the beginning 
and the camera station (decreased from this because of reasonable end 
height)) and the total duration will give some upper limit of the velocity.

Esko


>
> Question:  Can you determine the speed of a meteor using a single all
> sky camera?  If not a precise speed, can you roughly estimate the speed?
>
> Thomas Ashcraft in New Mexico
>
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