[meteorite-list] Wales image analysis

From: Matson, Robert <ROBERT.D.MATSON_at_meteoritecentral.com>
Date: Thu Apr 22 10:28:22 2004
Message-ID: <AF564D2B9D91D411B9FE00508BF1C86901B4EDD1_at_US-Torrance.mail.saic.com>

Hi All,

Okay, I've spent quite a few hours playing around with trajectory
solutions based on the two images (the original higher-zoom image
taken from Pencoed and the second wide-field shot taken from
Porthcawl). While it would be nice to have the exact coordinates
of the two observers, and some info on the fields of view of the
two images, the "flavor" of the solutions is not likely to change
that much. And this is where it gets interesting because those
solutions do NOT point to an object in level flight. In other
words, the rules of geometry are forcing me to reverse my
position and join the pro-bolide club!

Here's why. The wide field image from Porthcawl has the sun
in the field of view which allows one to place some reasonable
bounds on both the FOV of the image and the azimuths and
elevations of the trajectory. The track, if projected to
the horizon, would intersect somewhere in the azimuth 230-240
range. (At 6:15pm BST, the sun was at elevation 7.8 degrees,
azimuth 259.5 as viewed from Porthcawl.) If someone has a
more accurate estimate of the time of the image, please let
me know - the only reference I've seen is around 6 pm.

Now Pencoed is actually located ENE of Porthcawl (I'm using
a location 13.4 km east and 3.6 km north in my model). What
this means is that the sight lines to the contrail are
very similar from the two locations, and this is a problem.
You see, a constant-altitude contrail under these circumstances
would have to appear more steeply inclined relative to the
horizon as seen from Pencoed, and instead the contrail is, if
anything, slightly less inclined in the 15-year-old's image.
(By the way, the Pencoed image is not level w.r.t. the horizon;
the image needs to be rotated about 7 degrees clockwise to
align it with the Porthcawl image. But even after correcting
for this rotation, the Porthcawl slope is still greater than
that in the Pencoed image.)

I've tried a variety of reasonable values for the field of
view of the wide-field image, which in turn drives the time
of the exposure, the azimuth/elevation of the sun and the
azimuth and elevation ranges of the trajectory. Clouds
visible in both images can be used to determine corresponding
azimuths and elevations in the zoomed-in image. The result
is always the same: a steep, high altitude trajectory.

If someone can get an accurate time for the Porthcawl image,
and good coordinates for the two observers, I'll be happy to
compute a best fit triangulation solution.

Perhaps DoD will have a track on this object after all --
time will tell.

Cheers,
Rob
Received on Sun 05 Oct 2003 03:25:12 AM PDT