(meteorobs) Breaking News - Major TX, OK, AR, MO, KS, CO, NE Green, Fireball Meteor ~9:21CDT 23MAR2011

[Esko Lyytinen]

Hi all,

With some experience (maybe some dozens of (derived at least small 
fragment) falls, and many non-falls of course) of determining dynamic 
(with also other) masses of Finnish and some others fireballs, I was 
thinking if to try to make a more thorough analysis if this, but because 
of yet non calibrated cameras (with now even no access to star data), 
this would mean maybe a week of full time work. So I did not start this 
big work, but made some quick rough "checking".

I have earlier mapped the imaging geometry of some Sentinel cameras and 
used this data (assuming enough of similarity) to get the start and end 
altitude angle, with the assumed horizon location as a reference.
( I could quite easily get directions for Thomas Ashcraft camera, but 
this station was very distant, and the altitude angles near horizon 
(imaging geometry derived from star data) would not be as accurate as 
hoped for, so I did not measure these. Even this would need some star ( 
or city lights) checking, if the camera directions have been fixed since 
calibrated. )

The next is for the Oklahoma city vdeo.
I get the start elevation as 23 dergees and the end elevation as 32 or 
33 degrees.

In the video, the duration is 9 seconds. And the fireball is allready 
visible in the beginning and also in the end.

I ASSUME the true beginning height (in this camera) as 75 kilometers, 
(hopefully) consistend about to fit the rough velocity value, later in 
this. ( With a more sensitive camera and more nearby location (of 
start)n and considering that it is allready vislble, this would be a 
somewhat more high value with other circumstances.)
Wit this I get the ground distance as 168 km ( the true accurate is of 
course not so good).
( Have in the calculations none or less rounded values.)

IF we ASSUME the end height as 30 km, the ground distance to this is 
about 47 km.
The meteoroid comes allmost towards the camera. With this assumption the 
ground path would be 121 km. But taking into accout the fact that it 
came a bit aside, this would be roughly 130.
With this the average ground velocity is 14.5 km/s. Taking into account 
the slope (around 21 degrees, in these assuumptions) the average along 
the path would be 15.5 km/s. Noticing that it had deceleration, the true 
entry velocity might be around 17 km/s. ( could get a more elaborate 
value for consistency, but considering the over-all unecrtainty, may not 
bee needed.)
This is a good case for this kind off check because of the limited 
possible "space" of the track.

In the above, the end height  assumption is of course very uncertain, 
but IF it was more hight, this would mean a more slow entry velocity 
(and the contrary if more low).

I can not get a good calibrated magnitude value, but think that this is 
well brighter that Iridium -8, so maybe -10 ?
I try to get some integreted bightness value. I approximate maybe 5 
seconds at that mag -10 might give some level of an estimation (?)
Better calibrated values are welcome.

With the entry velocity and this value a formula for mass gives the 
entry mass as about 15 kg.
( I have not here the exact reference of this mass-formula, but this is 
from some oldish Canadian fireball-network publication. So this may not 
the best present date data, but is also about consistenet with our own 
derived dynamic masses.)
Assuming the ablation coefficient as 0.01 and entry velocity as 17 km/s, 
that 15 beginning.mass would give the end mass about 3.5 kg ( fragments 
combined ).

I also have my own non-published statistical formula for the masses and 
end heigth and slope. Data for this model is from oldish Canadian 
fireball-network pulication (table of derived end masses). And this 
seems to be more or less consistent also with my own dynamic mass 
determinations. For the data above (especially the assumed end height) 
this would give the end mass ass 4.5 kg.

I could make some iteration cahnge with the end eight to get these two 
mass-values equal. This ( to get a real fit of the values) would mean a 
slight increase of the end height. But the general uncertainties are so 
big that there is not much sense to do this. The statistical model in 
the original data set was in almost all cases good to about relative 
values of 1/3 or 3/1 and the magnitude estimation (above) of this 
firball is very poor.

We do not know the matherial of this instance, but also the Canadian 
data was not selected, although very probably mostly ordinary chondrites.

Do not take that above as an actual trial of exact derivation of the 
mass. The true error margins are quite big.
Its purpose is mainly to assume if this did fell a meteorite or not.
I myself am quite confident, but NOT very sure, that this fireball did 
fell down a meteorite of "moderate" size ( from maybe about one to 
several kg range, if ordinary chondrite ), and (some) smaller 
fragment(s). Others may disagree, this is ok, of course.

BUT, a low radiant angle, of course means a long dark flight. So even 
though (hopefully) getting the entry path well determined, the landing 
site location will not be so good.
( For similar size meteorites, lower entry agle also means higher 
luminous flight end height, that also ( in connection to the low entry 
angle) affects to lengthen the dark flight.)

Regards,
Esko