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-boun...@meteoritecentral.com] On Behalf Of Anne Black via Meteorite-list Sent: Tuesday, August 05, 2014 6:50 PM To: almi...@localnet.com; meteorite-list@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 impact...@aol.com -----Original Message----- From: almitt2--- via Meteorite-list <meteorite-list@meteoritecentral.com> To: meteorite-list <meteorite-list@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@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 > impact...@aol.com ______________________________________________ Visit the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://three.pairlist.net/mailman/listinfo/meteorite-list
