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(meteorobs) Fw: [MIAC-L] Instant solutions

    Dr. Jeremy Tatum has given me permission to re-post a message he sent to
the MIAC list regarding fireball tracking.  The message lists the minimum
requirements for arriving at a solution to determine the track of a
fireball.  Amateurs that observe fireballs or interview witnesses, should
take note of what is required to compute a track.  At the Edmonton meeting
of MIAC Jeremy stated that phone interviews are not good enough.  One should
interview the observer in person at the site the fireball was observed from,
reconstructing what was observed and making the necessary measurements.
Only then, can a plausible path be arrived at.

Ed Majden   -  MIAC Associate  - AMS Affiliate


 I am always amazed at the speed with which apparently precise instant
 solutions are announced, usually without any description of the method,
 following major fireballs.  The one thing that these instant solutions
 have in common is that they are not generally followed by finding a
 meteorite.

 Since I have spent some time thinking about how to track a fireball, I
hope colleagues will not mind too much if I am a little blunt. I shall
describe the MINIMUM information that is necessary to track a fireball from
(a) eyewitness accounts, and (b) seismological data.

 First:  Eyewitness accounts.

 In order to compute the track of a fireball through the atmosphere,
 the VERY LEAST amount of information needed are TWELVE (12) numbers, as
follows:

 For one witness:  1.  His latitude
                            2.  His longitude
                            3.  The altitude of one point on the sky track
                            4.  The azimuth of the same point on the sky
track
                            5.  The altitude of a second point on the sky
track
                            6.  The azimuth of that second point on the sky
track

 For a second witness:  The same data.


 If someone were to supply me, unambiguously, with these twelve numbers for
the Yukon fireball, I would be able to compute the path through the
atmosphere.

 HOWEVER, it must be STRONGLY EMPHASIZED that these twelve numbers are the
ABSOLUTE MINIMUM necessary to make a calculation possible.  If one of these
twelve numbers is missing, no calculation may even be started.  Having the
absolute minimum data, however, does not by any means
 result in a CREDIBLE solution.  For a credible solution, MANY witnesses
 must be interviewed, and the data required must be MEASURED and ALL of
 the conditions described in my talk in Edmonton MUST be satisfied.
 Unless all of these conditions are satisfied, colleagues must not imagine
 that even a remotely approximate solution can be obtained.  It cannot.
>

 Second:  Seismological records.
>
 In order that the position of the terminal burst can be computed from
 seismological records, the following TEN (10) numbers must be known
 unambiguously:

         1.  The time of arrival of the acoustic signal at a
              seismo station.
         2.  The latitude of that station.
          3.  The longitude of that station.
         4,5,6.  The same data for a second station.
         7,8,9,  The same data for a third station.
         10. The instant of occurrence of the terminal burst.

 If someone can supply me with these MINIMAL data, without ambiguity, I
 can calculate the position of the terminal burst.  Again, however, it
 must be very strongly emphasized that these are the ABSOLUTE MINIMAL
 data required to make a solution possible.  For a CREDIBLE solution,
 data for several more stations are required, as well as atmospheric
 data, including at least the temperature profile in the atmosphere.
 Further, the minimal data described above do not by any means tell
 whether acoustic signal is from a terminal burst or from the hypersonic
 shock front.
>
 Lastly, I would emphasize again that it is simply not possible, unless
 there is a MEASUREMENT of the VELOCITY of a fireball, to calculate the
 pre-encounter orbit of the meteoroid, without making additional
 assumptions such as what the pre-encounter orbit was.

 Sorry for being so blunt, but the fact is that none of the information
 that I have so far received makes it possible even to begin any sort
 of calculation of the path of the fireball.

 It is possible that the satellite data, given to a precision of
 0.05 degrees in latitude and longitude and 1 km in height, are more
 reliable.  The disadvantage, from the scientific point of view, is that
 these data, obtained as they are from military sources, lack the details
 of the method used, so that we cannot subject them to the usual
 judgment we make concerning the reliablity and precision of scientific
 measurements.  It would be interesting, for example, to understand
 the method that was used to measure the height of 25 km given for the
 terminal burst, and the extent to which errors in this measurement
 affect the calculated latitude and longitude.  Without this information,
 it is not possible for us to evaluate the reliability of the data.

                                           Jeremy  Tatum  -  MIAC


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