[meteorite-list] More on using NEXRAD for meteorite falls

From: Matson, Robert D. <ROBERT.D.MATSON_at_meteoritecentral.com>
Date: Mon, 24 Jan 2011 10:19:36 -0800
Message-ID: <9180F6B27399C541B10663E21C8BDE92F2D076_at_0461-its-exmb09.us.saic.com>

Hi Jim,

> I found my error. However, when I originally tried this about a month
ago,
> I could not duplicate 03:02:31. This was the biggest issue. I did
not
> capture this so I do not know why. Maybe I was using level III.

That's my guess.

> In any case, I was not changing the radial properties and I did not
catch
> that. When I fired it up this morning, I was actually getting a
radial
> properties pop-up screen, which I did not get before.

That screen is automatic for Level-II, but absent for Level-III since
Level-III data is single cut angle.

> That brought my attention to it and the default is very low...in the
> decimals.

The default is always 0.5 degrees -- the lowest cut angle. (The value
may
vary slightly from exactly 0.5 degrees, but it is always very close to
0.5).

> So I selected 15.69 and loaded that and there it was!! It is the only
> angle that shows it.

It was actually just a case of dumb luck that the radar got it at such
a high altitude. Think of it like a baseball hitter holding his bat out
and spinning in circles; when the pitcher throws the ball, the odds of
the hitter being phased exactly right to hit it are very low. However,
once the meteoroid breaks up into hundreds or thousands of individuals,
the odds improve dramatically that the radar beam will intersect some
of the meteoroid fragments when it sweeps through.

> This leaves me to wonder how 15.69 degrees was chosen. Were all the
> elevation angles checked or was it because of witness statements???

All elevation angles are manually checked for every radar and time
that is reasonably close to that of the fall time. Meteorites can
take up to 10 minutes to fall (though usually much less), so that
provides guidance on how many images to sift through.

--Rob
Received on Mon 24 Jan 2011 01:19:36 PM PST