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

From: Matson, Rob D. <ROBERT.D.MATSON_at_meteoritecentral.com>
Date: Thu, 7 Aug 2014 22:54:09 +0000
Message-ID: <4A4FA25E4DFE584AA580F4F069F9B4401CE2D3A3_at_EMP-EXMR104.corp.leidos.com>

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 06:54:09 PM PDT