(meteorobs) Final Report on fireball.

[Chris Peterson]

> ----Chris with all due respect, I was aware of both types of timing.
> BUT....he had to be using the internal time mode. It is also implied in 
> his
> comment below.

You can look at the EXIF header for the image and see that it was a 
120-second exposure. If it had been a 30-second exposure that would have 
been clear. Canon sells an inexpensive little programmable remote that most 
astroimagers use. It allows you to program in a sequence of images, with any 
duration, count, and interval. Almost certainly this is what was used. The 
EXIF value for "Shutter speed value" is "1.#INF00 s", which is certainly 
odd, but it's also what I see in the header of images from my 300D when I'm 
in bulb mode.

> ----CCD & CMOS substrate response to IR wavelengths. (bloom.), "AKA heat
> smear" or a blooming which washes(saturates) an image of visible light
> detail. :-) -Larry

Blooming is an artifact produced by most CCDs and by few CMOS detectors. The 
Canon sensor, for instance, does not bloom. There is no blooming in the 
meteor image under discussion, but there is saturation. This is hard to 
analyze with the eye, because our response to intensity is highly 
non-linear. However, you can convert the intensity to color and easily get a 
good sense of what is going on in the meteor, and where things are 
saturated. I've done that here: 
http://www.cloudbait.com/misc/swanson_meteor_int.jpg . About all the 
original image is good for in terms of analysis is seeing the typical green 
atmospheric oxygen emission early in the path, before it gets washed out or 
saturated, and for seeing the color of the plumes (which appear to be the 
same pale orange color almost always seen in persistent trains).

Silicon sensors can potentially detect light out to about 1 um, which is 
(very) near IR, not really far enough out to be considered a heat signature. 
It is important to remember that the IR output of meteors is not very high. 
There are only a few weak emission lines out around 1 um, and any blackbody 
component is much stronger in the visible than in the IR. The fact that the 
camera doesn't image IR probably has very little impact on the final image, 
other than the background color balance. Meteors output far more energy in 
the visible range than they do in either the near or far IR.

Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com


----- Original Message ----- 
From: "Larry" <ycsentinel at att.net>
To: "Global Meteor Observing Forum" <meteorobs at meteorobs.org>
Sent: Wednesday, September 23, 2009 12:19 AM
Subject: Re: (meteorobs) Final Report on fireball.


>
> ----- Original Message ----- 
> From: "Chris Peterson" <clp at alumni.caltech.edu>
> To: "Global Meteor Observing Forum" <meteorobs at meteorobs.org>
> Sent: 2009/09/22 21:26
> Subject: Re: (meteorobs) Final Report on fireball.
>
>
>>> If the fireball passed through the eye of a strong CCW CIRCULAR high
>>> altitude wind pattern on an oblique angle of approach or recession
>>> relative
>>> to the cameras position, the differing plume curvatures could be
>>> accounted
>>> for.
>>
>> The fireball is luminous through a vertical distance of about 35 km. The
>> angle of approach is not very oblique. These characteristics can be
>> determined (within a fairly narrow range) since the speed of the meteor
>> and
>> its distance from the radiant are precisely known, and its height when
>> first
>> becoming luminous can be reasonably estimated.
>
> ------I am skilled enough to argue that. -Larry
>
>>> First of all, Canon Mfg. informed me that this camera would take 1 full
>>> frame capture every 30 seconds in timed shootings. A 2 minute time shot
>>> would contain 4 full frame electronic captures.
>>
>> This is not correct; you have misunderstood the camera operation. The
>> camera
>> is perfectly capable of taking a single 2-minute exposure, and the EXIF
>> header in the file leaves no doubt that it did so in this case. The
>> 30-second limitation is merely the longest internally timed exposure that
>> is
>> possible. In the bulb position, with an external release or the standard
>> Canon remote control, there is no time limit. This image is a true
>> 2-minute,
>> single exposure.
>
> ----Chris with all due respect, I was aware of both types of timing.
> BUT....he had to be using the internal time mode. It is also implied in 
> his
> comment below. Besides....WHO would stand there for 3 hours operating the
> shutter control every two minutes for a total of 90 times in bulb
> control?.....especially since he could just let the camera do it
> automatically with the same results while he observed through the LX200 
> and
> made drive corrections? -Larry
>
> "I set my camera up piggybacked on my LX200R to take 2 minute shots for
> several hours. When I was searching thru the photos, I noticed that I was
> able to catch several dim meteors. Then the second to the last shot before
> sunrise made my jaw drop!"
>
>
>>> The time period of most fireballs that we record like this would 
>>> probably
>>> be
>>> about 5 to 7 seconds.
>>
>> In fact, using the same geometric calculations mentioned above, it is 
>> easy
>> to determine that the meteor duration was 2-3 seconds. This is also
>> consistent with typical fireball durations for fast meteoroid streams. A
>> 5-7
>> second duration would require a much shallower path, and would be unusual
>> for a 66 km/s stream. Such long events usually suggest a much slower, 
>> more
>> massive body.
>
> ----Again, I cannot argue your conclusions. But I instinctively shy away
> from rigid conclusions based on it being from a specific radiant without 
> any
> chance it could be a SPO or that the estimates could not contain
> error...... -Larry
>
>
>>> The heat smears we normally would expect to see from a fireball 
>>> composite
>>> or
>>> timed photograph WILL NOT BE PRESENT.
>>
>> I've read a lot of papers about meteors, and I've never encountered this
>> concept of "heat smear". Could you please explain what you mean by the
>> term?
>>
>> Chris
>
> ----CCD & CMOS substrate response to IR wavelengths. (bloom.), "AKA heat
> smear" or a blooming which washes(saturates) an image of visible light
> detail. :-) -Larry
>
>
>> *****************************************
>> Chris L Peterson
>> Cloudbait Observatory
>> http://www.cloudbait.com
>>
>>
>> ----- Original Message ----- 
>> From: "Larry" <ycsentinel at att.net>
>> To: <meteorobs at meteorobs.org>
>> Sent: Sunday, September 20, 2009 11:34 AM
>> Subject: (meteorobs) Final Report on fireball.
>>
>>
>>>I too have had trouble keeping the tumbling and outjetting concept
>>>together.
>>> Details in the picture were both for it and against it. Tumbling 
>>> "seemed"
>>> to
>>> be the CLOSEST solution in solving both upper and lower stream 
>>> curvatures
>>> &
>>> the apparent periodic nature of emissions from this fireball in flight.
>>>
>>> Notably smearing is absent at & near the base of the "outjetting"
>>> streams.
>>> Smearing should have occured if there was any kind of *oblique tumble
>>> during
>>> periods of jetting. (* Needed to account for differing upper and.lower
>>> stream curvatures.).
>>>
>>> The same lack of smearing coupled with the apparent stream curvatures in
>>> opposition did not match conventional fireball ablation or other
>>> photographs
>>> of timed & composite imaging of events. Forum presented arguments were
>>> not
>>> comprehensive enough to solve at the same time, the stream curvatures 
>>> and
>>> what appears to be descrete ejection or emissions.
>>>
>>> So back to square 1.
>>>
>>> If the fireball passed through the eye of a strong CCW CIRCULAR high
>>> altitude wind pattern on an oblique angle of approach or recession
>>> relative
>>> to the cameras position, the differing plume curvatures could be
>>> accounted
>>> for. But still not accounted for is the lack of smearing at the base or
>>> points of stream origin. Each stream appears sharply defined and
>>> separated
>>> without significant smear.
>>>
>>> Canon appears to be a major part of the answer.
>>>
>>> First of all, Canon Mfg. informed me that this camera would take 1 full
>>> frame capture every 30 seconds in timed shootings. A 2 minute time shot
>>> would contain 4 full frame electronic captures. Trivia--I also read that
>>> it
>>> takes 1 frame(part?) every 15 seconds which I believe meant combined to
>>> produce 1 full frame image in 30 seconds.
>>>
>>> The time period of most fireballs that we record like this would 
>>> probably
>>> be
>>> about 5 to 7 seconds. The contrast and sharpness of this fireball
>>> compared
>>> to the star field, and the fireballs failure to burn out or detonate
>>> suggests the camera concluded the last(4th) 30 second full-frame before
>>> the
>>> fireball may have ended its travel.
>>>
>>> Results of checking the Canon 20D specifications:
>>>
>>> The 20D has a very special IR filter and processing which makes all of
>>> its
>>> photographs look the same as it would actually look through a human eye!
>>> This CMOS camera HEAVILY filters out IR and as I read it, UV wavelengths
>>> too, so that it records only the narrow band of VISIBLE light. Herein is
>>> the
>>> problem!
>>>
>>> The heat smears we normally would expect to see from a fireball 
>>> composite
>>> or
>>> timed photograph WILL NOT BE PRESENT. This also accounts for the extreme
>>> sharpness and resolution right down to the needle-like tail on the
>>> fireball.
>>>
>>> I do not know if we can be certain on the size(mass) of this fireball
>>> especially since this camera apparently was sold with a 55mm lens.
>>>
>>> Now guess where I am going........... Either this fireball zipped down 
>>> on
>>> an
>>> oblique angle after "lingering" in a circular wind stream for a few
>>> seconds..... :-}
>>>
>>> Or..... it zipped down tumbling or spinning on an oblique angle relative
>>> to
>>> the camera.
>>>
>>> Summation of evidence:
>>>
>>> 1) Previous negative photographs.
>>>
>>> 2) UV & IR stripping of Canon 20D photographs.
>>>
>>> 3) Text contained in NASA site regarding meteor spin and jetting. See
>>> subject "Spinning Meteors" under 1999 Leonid MAC results. (Normal URL
>>> without the www stuff) .....leonid.arc.nasa.gov/
>>>
>>> I believe this should put a good wrap on Ashcrafts discovery, and ends
>>> further investigation on my part.
>>>
>>> Larry -YCSentinel
>>>
>>> (Hope this post got through.)
>>
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