(meteorobs) 2012/02/01 TX Fireball

Thu Feb 9 06:48:35 EST 2012

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 solutions
>    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 nasa.gov
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