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Re: (meteorobs) radio observations during enhanced meteor activity



* On monday, 11/17, I had written:


"0630 CST / 1230 UT - 

Combining morning sporadics and Leonids together, the radio becomes a
continuous din of activity.  Some light ES is also evident now.

The activity reminds me of a radio account of the 1946 Giacobinids, in
which the meteor activity essentially created a continuous layer of
electrons, blending all incoming meteor events together in one long event.  "

and:

"It is also obvious that the duration and power enhancements caused by
forward-scatter (as compared to back-scatter) would make monitoring actual
storm conditions from this shower quite difficult using this system, due to
the "overlapping" effect described above.  A higher operating frequency and
shorter range would help to counteract this."


*  Considering the same morning of activity, Tom Ashcraft wrote:

"The following 1300
UT hour is a continuation of the pattern but receptions are nearly
continuous with many multiple FM transmitters being received. I see no way
to count individual reflections but there is a dynamic reflection layering
with reflections punctuating reflections puncuating reflections.  It would
be difficult to arrive at any "peak" Leonid moment as the 1300 UT hour
mixes with highest morning sporadic meteor rates but 1348 UT to 1354 UT is
noted on my chart as particulary dense. "


* Prompting Sirko to write:  

>
>I think this shows quite clear, that we can't rely on radio observations
>for the 98/99 Leonid maximums. If the 'big bang' really happens, all radio
>systems will probably be completely saturated. Wasn't it the same problem
>back in 1966?
>Any idea how to overcome the fault? Any experiences how to cope with that
>type of saturation from the AMS Radiometeor experts?


Hello Sirko,

Your last statement has me squirming uncomfortably.  Let me plainly state
that I have never claimed to be any sort of "expert" in this field.  All i
have to do is read a chapter in McKinley or talk to a Ph. D. researcher in
this area to reinforce the fact that i am a very tiny fish with an aweful
lot yet to learn.  

With that in mind, here are a few more of my (amateur) thoughts on this topic:

There are ways in which the saturation problem might be reduced in
magnitude.  The sticky point is that these solutions are counter to why
forward-scatter works so well, and counter to the steps that amateurs take
to enhance their system capabilities to see fainter and fainter meteors.
Most of us attempt to equip ourselves with the most sensitive radio
equipment that we can buy or build.  By moving down to lower operating
frequencies, and increasing the distances between transmitter and receiver
you also increase the returned power and duration of a meteor when compared
to the back-scatter situation.  Thus, you also push the "limiting
magnitude" for the system to fainter levels and exponentially increase the
numbers of meteors "seen."

At the same time, you also make the system more easily saturated by such
things as Sporadic E, spread F, Aurora, temperature inversions, etcf. --
the "clouds" of the radio observer.  For the most part, however, saturation
due to meteors is not normrmally a concern!

The Leonids are the most unique meteors with regard to radio reflections
that I have ever encountered.  They are the only shower members which I can
frequently identify by ear:  due to the fast meteor head-echo, their
transition-event quality of suddently slamming the radio from low peg to
high peg, and extremely long durations.  On a normal day, i might get a
scattered handful of sporadic events with durations over 1 minute.  The
Leonids make this look like the norm!    

Thus, an enhancement of bright Leonids is likely to saturate almost any
forward-scatter system, unless perhaps the frequency is quite high -- such
as in the 2-meter (144-148 MHz) amateur band.  Even then, I don't know, as
Tom reached saturation in the commercial FM band (88-108 MHz), nearly 40
MHz above my own system.  Utilizing closer transmitters would also help,
but this is not often very feasable, due to saturation from the
transmitter's tropospheric scatter signal.

The back-scatter radars will fare better, due to the very high incidence
angle of the reflection (90 deg), especially those at higher frequency.  I
am looking forward to hearing how the installations at Arecibo, Edwards
AFB, and London, Ontario, did during this event.  

One final thing to keepin mind.  Based upon the Giacobinid account, it
might be possible for the incoming meteor flux to reach the point that the
E-layer itself saturates, in which case it won't make much difference what
your system configuration is.  The system would see a continuous strong
signal, perhaps punctuated by some stronger single events.  It will be
interesting to see if individual events and shower rates can still be
picked out during this condition -- if it indeed even occurs.  The
professionals now are much better equiped than they were in 1966.

Best regards,

     Jim


James Richardson
Graceville, Florida
richardson@digitalexp.com

Operations Manager / Radiometeor Project Coordinator
American Meteor Society (AMS)
http://www.serve.com/meteors/


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