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

[Esko Lyytinen]

After writing that below, I remebered one previous case where I had a 
fast fireball from allsky camera, first from one station only and then 
had a second camera data and the one station result proved resonably 
good, with an accuracy of about two degrees in the entry direction.

Esko

> 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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