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

[Esko Lyytinen]

Hi Chris,

You are right that narrow field cameras suit this better, if a long 
track gets obseved in the field.
Especially if a distant short meteor track is seen in only one all sky 
camera then there is not much hope of getting any usable result. But if 
the camera is well calibrated and a nearby meteor makes a long apparent 
track in the camera, like the Cranbrook video in May 13/14 this should 
be successful. In this case the very bright fireball spread a lot in the 
image and this made it more difficult to measure, but successfull 
especially for a good part of the track near the beginning (which is 
more importan to this as told) with manual frame measurments.

We here in Finlad (fireball observing group) have a number of allsky 
cameras and more narrow field cameras and it is of course case dependent 
what we may get. And in many cases the observational data is not as good 
as one would hope, of course. There has been propable good meteorite 
droppers that were observed from only one camera, but now I do not 
remember any such here in only one allsky camera.

(
In some cases automatic directions are available (from UFO-prgrams for 
example) for all frames, but if these have to be measured manually then 
I typically measure only some of these like every fifth for exaple, IF 
there are several seconds of recording. For expected good meteorite 
droppers, all frames of the end track are measured even when having to 
do this manually, to get the velocity and deceleration near the end well 
derived (resulting to dynamic mass value and hopefully good dark flight 
modeling) .
)

Esko

> Hi Esko-
>
> Have you had much success doing this with relatively low resolution
> allsky video, or mainly with narrower field data? I've tried doing this
> with single station data using a second station to check, and haven't
> gotten consistent results at all.
>
> Chris
>
> *******************************
> Chris L Peterson
> Cloudbait Observatory
> http://www.cloudbait.com
>
> On 6/3/2011 12:02 PM, Esko Lyytinen wrote:
>> 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
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