[meteorite-list] Meteorite falls, NEXRAD changes and recovery rates

From: Anne Black <impactika_at_meteoritecentral.com>
Date: Thu, 7 Aug 2014 22:26:40 -0400 (EDT)
Message-ID: <8D180C751FCB971-2C18-4622_at_webmail-m232.sysops.aol.com>

Thank you Rob,
Thanks for the clear and thorough explanation.
Yes, radar was not invented to please meteorite-hunters.
It would have been nice, but ..... back to the old ways!


Anne M. Black
www.IMPACTIKA.com
IMPACTIKA at aol.com


-----Original Message-----
From: Matson, Rob D. <ROBERT.D.MATSON at leidos.com>
To: Anne Black <impactika at aol.com>; almitt2 <almitt2 at localnet.com>;
meteorite-list <meteorite-list at meteoritecentral.com>
Sent: Thu, Aug 7, 2014 4:54 pm
Subject: Meteorite falls, NEXRAD changes and recovery rates


Hi Anne,

Thanks for the shout-out regarding meteorite recovery via all-sky
camera
triangulation and
Doppler radar. I have some bad news as far as the radar angle that I
thought I
would share,
which may help explain some of the recent downturn in meteorite
recovery rates
-- at
least in the U.S.

Sometime in the last year or two, many (possibly most?) NEXRAD radar
sites
changed
their operating modes to support dual polarization. Some have argued
that this
would
not result in a loss of sensitivity, but only an improvement in
differentiating
weather
phenomena from other "noise" features (e.g. birds, bats, bugs,
meteorites,
ground return).
But from a "meteorite-to-be" detection perspective, Marc Fries and I
would much
prefer
that no filtering of the radar data take place: we WANT to see all
that noise.
Unfortunately,
the level-2 data that is provided by NOAA has clearly undergone some
degree of
processing, and the combination of the change in operating mode coupled
with
that
processing has resulted in a definite loss of sensitivity to the very
phenomenology that
interests us (but is of little interest to meteorologists, in spite of
their
name. ;-)

Marc tells me that the sensitivity appears to have dropped by 3 dbZ,
which may
not
sound like a lot, but it's a 50% power drop off. If you revisit some
old falls,
and cut their
radar signatures in half, they become much more difficult to recognize.
For
instance,
Marc went back and looked at Ash Creek (West, TX) and said that a 50%
drop in
the
sensitivity would have removed 90% of the radar returns.

Knowing this, it goes a long way toward explaining why none of the
seemingly
spectacular bolides of the last year have had "in your face" radar
returns -- to
include
this most recent falls in southeast Virginia and on the northern
Alabama/Georgia
border. Both of these were almost certainly meteorite-producing events,
and yet
I worry that folks have become so dependent on radar data that when it
isn't
forthcoming it means it's not worth pursuing. Hopefully this message
will make
clear
that the old school approaches based purely on optical triangulation
are still
very
valid, and with or without corroborative radar are worth chasing.

For our part, recognition of the radar operating mode change has
alerted Marc
and me to lower our thresholds and look for noise-floor-level returns
that
spatially correlate with fall locations determined by optical means.
--Rob

-----Original Message-----
 From: Meteorite-list
[mailto:meteorite-list-bounces at meteoritecentral.com] On
Behalf Of Anne Black via Meteorite-list
Sent: Tuesday, August 05, 2014 6:50 PM
To: almitt2 at localnet.com; meteorite-list at meteoritecentral.com
Subject: Re: [meteorite-list] GA NC TN AL KY Meteor Approx 2320 EDT //
2220 CDT
02AUG2014

Thank you Al!
You are the only one who responded.

Yes, of course a lot of meteorites are lost to the oceans, lakes, and
to remote
areas. And it is interesting that the best year for Falls is 1933. Of
course I
certainly would not expect the average rate of Falls to change over the
years,
but with radar, all-sky cameras, computers, fast communications, all
the work
 from Dirk Ross, Rob Matson and several others, and a lot more people
looking up,
I would expect the percentage of recoveries to go up.

But is it?
Or is all our modern fancy equipment all for naught?


Anne M. Black
www.IMPACTIKA.com
IMPACTIKA at aol.com


-----Original Message-----
 From: almitt2--- via Meteorite-list
<meteorite-list at meteoritecentral.com>
To: meteorite-list <meteorite-list at meteoritecentral.com>
Sent: Tue, Aug 5, 2014 7:24 pm
Subject: Re: [meteorite-list] GA NC TN AL KY Meteor Approx 2320 EDT //
2220 CDT 02AUG2014


Hi Anne and all,

There are many scientifically calculated fall rates. Most assume
meteorites that have landed are 100 grams or larger as those are deemed
more findable. A Canadian study estimated some 21,000 falls per year.
We loose 3/4 in the oceans, leaving some 6,000 to land on dry land.
Many of those land in remote areas away from the notice of people.
Higher populations usually result in the notice of more falls. Light
pollution probably reduces that number some.

Of all the falls, only 0.1% or about 5 to 6 falls per year are actually
collected. The 1933 year was an excellent year for recovery of falls.
17 meteorites of the potential fall total were recovered!

According to this Canadian study we are really no better at recovery of
falls than we were in the past. Even though meteorite falls are better
understood than in the past. It is important to keep this in mind as
there are many unlocated falls all over the world.


Source for some of this information:
Canadian fireball rates and meteorite falls ? declining returns
by
Martin Beech
Campion College, The University of Regina, Regina, Saskatchewan, Canada


--AL Mitterling
Mitterling Meteorites

Quoting Anne Black via Meteorite-list
<meteorite-list at meteoritecentral.com>:

> I am curious.
> It is practically everyday that a fireball is spotted somewhere
> around the globe, but......
>
> - How many of those "fireballs" are real fireballs, not plane,
> fireworks, lighting,....... etc?
> - How many of those real ones burn up in the atmosphere?
> - How many make it to the ground and produce meteorites?
> - And finally how many of those are ever found soon enough to be
> called Falls?
>
> Is anyone keeping track of those numbers?
> The percentage meteorites <> fireballs would be interesting.
>
>
> Anne M. Black
> www.IMPACTIKA.com
> IMPACTIKA at aol.com

  
Received on Thu 07 Aug 2014 10:26:40 PM PDT