(meteorobs) 2012/02/01 TX Fireball

Thu Feb 9 13:05:05 EST 2012

Hi Pat and others,

No that is not a point where the ground track itself passes. The local 
azimutal and altitude angles shift all the time when it moves at a long 
ground path, especially in this case because of the long track. So when 
these are specified, it is proper to say at which reference location the 
directions apply. Maybe this confuses, beause that given is even not at 
the track.

I make my actual calculations in a cartesian three dimensional 
coordinate system. The X-Y plane is tangent to the ellipsoidal Earth 
sea-level surface at some specified point, and all camera coordinates 
are calculated to this and also all local az. and alt. coordinates are 
changed to this system. All directions (observations and also the 
direction of motion) are calculated in this and the az 0 is the North of 
this origin location, and so also the radiant az and altitude angles are 
calculated in this and given further according to this.
This origin is selected beforehand when not knowing where the tack goes. 
This can be later changed with minimum labour, but if it gets reasonable 
nearby, I may not much change this, if not needed for some special 
purpose, for example.

If one does not need the radiant directions with big accuracy (another 
question is if it gets derived as accurant at all in a special case), 
then one does not need to consider the given origin reference point at 
all. Then you may forget this 32.50 , -97.00 .
Now the derived track passes just 11 km North of that given origin 
rerence point. (As you say, the track is 11 km South of this point. I 
get the most near direct ground distance as 11.85 km from my solution.)

Esko

> Can you clear up what you mean by "32.50 N, 97.00 W as a reference". You mean your track passes thru that point? That is about 11km south of Bill's track, which is at the southern edge of the various video tracks we have.
>
>
> --- In meteorobs at yahoogroups.com, Esko Lyytinen<esko.lyytinen at ...>  wrote:
>>
>> Hi,
>>
>> I have also have made the modeling and fit (from almost he beginning
>> after the fall) of this from quite well calibrated cameras of OKC,
>> Hawley and Coleman, kindly supplied to me by James Bauchamp and Kevin
>> Palivec in a more original form that found in the net. I also have in
>> this the frame directions that Bill Cooke earlier gave in meteorobs.
>> Thanks to Bill, James and Kevin ! I also had some email change of
>> thoughts and early solution data on this with Bill, as Bill also tells.
>>
>> I started this because I earlied had calibrated the OKC camera, that now
>> however needed some check and "rotation" by means of stars, now only a
>> few seemed to be needed. (More can be measured and may to some degrees
>> improve the directions. And especially low elevation reference would be
>> needed.)
>> The first purpose was mainly to get to know for sure, if this is of
>> meteoric or satellite origing.
>> Getting a resonable solution originally from OKC camera and Bill's data,
>> I continued by calibrating the Hawley camera from 16 stars and the
>> Coleman camera from 13 stars.
>> The direction data from Bill, is now in principle included in the
>> solution, but with the given weigh practically not affecting in this.
>> But these are seen to to be very well consistent with the solution, even
>> better than one might expet. The general trend in these is sen to be
>> within about 0.1 degree. ( The mutual "scatter" is bigger than this.) I
>> don't even know if the amospheric refraction has been "removed", but as
>> given (not corrected by me for the refraction) these do have the very
>> excellent fit to the entry track fitting. Maybe this good fit, is good
>> luck in part.
>>
>> My ground track is very close to that of Bill's !
>> In the beginning the ground track differs by about 1.5 km and in the end
>> by only about half a kilometer (from that given in meteorobs, seen below
>> for the solution  ".. all other solutions put ..").
>> The beginning height is the same to a kilometer (at 92 km), but I have
>> the end clearly more low, at 30 km.
>>
>> I get it arriving from az. direction 255.6 with the slope of 12.2
>> degrees. The reference meridian and horizon to these values is 32.50 N,
>> 97.00 W.
>> In the solution, the track is not a straight line, but the Earth gravity
>> is put to affect in it during the first 11.3 second of flight. The
>> reason not to have put this in the whole flight is that with strong
>> deceleration (which would also in part decelerate the Earth "already
>> gained" gravity effect, which is not taken into account properly in the
>> program, even though normal deceleration is (more or less well) ) the
>> gravity effect would easily get overcorrected in the end.
>>
>>   From the deceleration I get the end mass (assuming normal chondrite
>> density) of about 30 kg.
>> With what I think as a reasonable ablation behaviour, I get the
>> beginning mass of around 100 kg (and whole flight modeled with these).
>> This is well within the values by Bill Cooke, from bightness and light
>> efficiency.
>> This mass-estimation from deceleration is however strongly dependent on
>> the true height of the end path and I am still hoping for new data to
>> better calibrate the camera ( especially the OKC camera) at the relevant
>> quite low altitude angles. And also the mass estimatoin is affected of
>> where itfrag,ented and how much. If it fregmented after ( or arond)
>> disappearing from the OKC camera, the value would in principle be the
>> total mass. But if fragmented well before this, tha mass value would
>> (more or less) refer to the biggest mass or masses. For the end path
>> deceleration derivation, the OKC data is the most relevant, as fitted
>> with the others also.
>>
>> I have the beginning velocity a little more than 16 km/s.
>>
>> Regards,
>> Esko
>>
>>
>>> We have spent the last few days analyzing the Sandia camera videos kindly provided by James Beauchamp and Kevin Palivec (also thanks to Esko Lyytinen for his insight and comments). These have enabled us to determine a decent trajectory for the meteor; unfortunately the meteor entered at a shallow angle and its path/duration was so long (18.5 seconds) that the linear approximation used in the trajectory codes (MILIG, courtesy of J. Borovicka, and SMETS) is not valid, resulting in a possible error of several (~5) kilometers in the final position. Consequently, we did not attempt the dark flight calculations needed to determine the impact zone, as an error of 5 kilometers in position at 30-40 km altitude would translate to over a hundred square kilometers of uncertainty in the meteorite fall area. I can say that a solution using the first hundred frames of video (meteor is above 65 km altitude) yields a trajectory consistent with the Edgewood doppler returns; all other solut
>   io
>>   ns
>>>     put the meteor path about 20 km to the north of the radar signature.
>>>
>>> Here are the beginning and end coordinates of the meteor, based on a solution involving all 976 points (frames) from the 3 videos:
>>>
>>> Meteor beginning point: 99.176 W, 32.108 N at an altitude of 92 km
>>> Meteor end point: 96.357 W, 32.745 N at an altitude of 43 km
>>>
>>> Mean residuals in trajectory fit (residuals show systematic trends due to breakdown of linear path approximation)
>>>
>>> Coleman: -0.045 km vertical, 0.703 km horizontal
>>> Hawley: -1.889 km vertical, -1.711 km horizontal
>>> OKC: +1.302 km vertical, -0.123 km horizontal
>>>
>>> Again, the end point is NOT the impact location; it represents the meteor position in the last frame in the OKC all sky camera video.
>>>
>>> Average speed is 16.3 +/- 1.4 km/s
>>> Initial meteor speed: ~18 +/- 1 km/s
>>> End meteor speed: 9.8 +/- 4 km/s
>>>
>>> I am confident this meteor produced meteorites. Seen by our camera way over in New Mexico, it was very bright, with peak absolute magnitude around -14 (lower limit). Mass estimates from the light curve range from about 20 kg to just over a metric ton (1017 kg), depending on whose equations/technique you use. I consider a few hundred kg likely, but would find it hard to argue against the metric ton figure. How much mass made it to the ground is anyone's guess, but be assured that this was a BIG rock that blazed across the Texas sky.
>>>
>>> The gory details are in this pdf file: http://www.billcooke.org/events/20120202_0157.pdf
>>> The complete meteor trajectory (text file) is here: http://www.billcooke.org/events/smets.txt
>>>
>>> Reference for MILIG: Borovicka J.: The comparison of two methods of determining meteor trajectories
>>> from photographs. Bull. Astron. Instit. Czechoslovakia, 41, 391-396 (1990)
>>>
>>> Regards,
>>> Bill Cooke
>>> NASA Meteoroid Environment Office
>>> Marshall Space Flight Center
>>> Email:william.j.cooke at ...
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>>> http://lists.meteorobs.org/mailman/listinfo/meteorobs
>>>
>>
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