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ON1DHT > VLF 16.11.00 22:35l 109 Lines 5162 Bytes #-8884 (0) @ EU
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Subj: Sientists & Hams -> Meteors
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Sent: 001116/1207Z @:ON0OB.#OVN.BEL.EU #:17702 [OUDENAARDE] FBB7.00g $:17702_ON
From: ON1DHT@ON0OB.#OVN.BEL.EU
To : VLF@EU
Meteor Balloon Rises Again
--------------------------
Scientists and radio amateurs team up for a live webcast of the 2000
Leonids from the stratosphere!
November 9, 2000: On Nov. 17 and 18, 2000, space forecasters expect a
series of Leonid meteor outbursts with flurries possibly exceeding 100
shooting stars per hour. Observers in Europe, Africa, and the eastern
half of the United States and Canada are generally favored for best
viewing, but the Leonids are notoriously unpredictable. Everyone,
everywhere should remain alert for meteors during the hours before
local dawn next Friday and Saturday.
Before dawn on Saturday, Nov. 18th, a team of astronomers and ham
radio amateurs at NASA's Marshall Space Flight Center (MSFC) plan to
launch a specially-equipped weather balloon to monitor the Leonid
meteor shower 100,000 feet above Earth's surface, far from obscuring
clouds and urban light pollution. Video from the flight will be
broadcast live on the web at LeonidsLive.com and replays will be
available less than 24 hours later.
This will be the third annual SienceNASA sponsored broadcast of the
Leonids from the stratosphere. In 1998 and 1999 more than two million
people watched live webcasts during the meteor shower or saw replays
the morning after.
This year's liftoff is scheduled for 0630 Greenwich Mean Time (0030
CST) on Saturday, Nov. 18th, from the Marshall Space Flight Center's
Atmospheric Research Facility (ARF). The balloon will carry a
sensitive low-light CCD video camera to monitor the shower from an
altitude of about 32 km (100,000 ft).
"Earth is going to pass through the outskirts of three meteoroid
debris streams from comet Tempel-Tuttle on Nov. 17th and 18th," says
Marshall astronomer Mitzi Adams. "The last of the three stream
encounters will take place at approximately 0800 GMT on Nov. 18th,
just as the meteor balloon is reaching its maximum altitude. The
timing couldn't be better."
"The balloon will carry a sensitive CCD camera to record the meteors,"
added Ed Myszka, an engineer and radio amateur who built the balloon
payload. "The field of view will be about 20 degrees. That's about
twice the size of the bowl of the Big Dipper.
"We plan to downlink the video to our ground station at the ARF as an
amateur TV signal at 426.25 MHz -- that's Cable Ready TV Channel 58.
The transmission should be detectable for several hundred miles around
the launch site. Hams in the vicinity of north Alabama and Tennessee
will be able to monitor the flight themselves. And of course the video
stream will be available for everyone on the web at LeonidsLive.com."
Sound effects during this year's flight will be provided by an VLF
radio receiver, which is sensitive to radio emissions below 10 kHz.
The very low frequency (VLF) radio band is filled with exotic-sounding
signals called spherics, tweeks and whistlers. All three are impulsive
bursts caused by distant lighting. "Spherics," which are caused by
lightning strokes within a couple of thousand kilometers of the
receiver, sound like twigs snapping or bacon sizzling on a grill.
Tweeks and whistlers are caused by more distant lightning, and sound
like brief descending musical tones.
Dennis Gallagher, a plasma physicist at the Marshall Space Flight
Center, thinks that the VLF receiver might also pick up natural radio
emissions from the Leonid meteors.
"Meteoroids produce an ionized trail as they plow through the
atmosphere," explained Gallagher. "There's a low density wake right
behind the meteoroid. Because electrons are more mobile than protons,
they move in to fill the void faster. That could set up plasma
oscillations and trigger radio emissions."
The VLF receiver was donated to the Marshall Space Flight Center for
this and future flights by the Goddard INSPIRE program. It's been
christened the "Marina receiver" after the daughter of Flavio Gori, an
Italian scientist who first suggested flying the receiver.
Gallagher and his colleagues also plan to operate another VLF receiver
at the launch site to provide a ground reference for comparison with
data collected from the stratosphere. During the flight, signals from
the receiver will be converted to audio sounds and transmitted along
with images from the CCD video camera. Web viewers at LeonidsLive.com
will be treated to an unusual combination of meteoritic sights and
sounds.
The question of radio emissions from meteors is an intriguing one,
says Gallagher, and you don't need to send your receiver to the
stratosphere to listen in. Anyone with a VLF receiver can monitor the
Leonids on November 18 and Gallagher hopes that INSPIRE participants
across the USA will join in the effort. The best way to collect data
is to record the output of the receiver on a two-track audio recorder.
Record the VLF signal on one track and a WWV time signal on the other.
This way VLF pulses can be correlated with the times of bright meteors
seen from your observing site. It's also a good idea to conduct at
least one observing session a few days before or a few days after the
Leonids for comparison.
73"
Guy, de ON1DHT
source: Sience@NASA
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