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Re: (meteorobs) upper winds and meteors



Lewis,

At 09:41 AM 5/30/97 -0400, you wrote:
>Hi, Brian, is the question you're asking simply whether or not doppler
>radar can pick up meteor trails? That's a good one: my untutored opinion is
>that it certainly could, since radar has been used extensively in the past
>to do meteor research (using a technique called "radiometeor backscatter",
>I guess). There are certainly others on the list who could answer this
>question in MUCH more detail! How about it, Tom, Jim(s), Werfried, et al?


Ummmm...I dislike being a naysayer, but based upon my limited knowledge of
doppler radars, I don't think that they can be used to detect meteors.
There are a few reasons for this:

1.  Weather and surface radars operate in the Giga-hertz frequency range,
which is far too high for meteor work.  The scatter signal from the meteor
trail would have an extremely high loss, and the attenuation due to
distance would also be quite high.  

The "classical" meteor radar generally operates between 30 and 50 MHz, with
modern facilities, such as Arecibo, working up to 430 MHz.  I know of one
special radar in Sweden which has done some experiments as high as 900 MHz,
but this is quite uncommon.  Such facilities look straight up at the
closest meteors, which are still 90 to 100 km away, and the returned signal
is restricted to the meteor head area, rather than the trail.

2.  Doppler radars are surface radars, with very small, rotating
directional beams, generally directed toward the horizon.  Meteors within
this narrow beam would be several hundred kilometers away at these low
elevation angles.  The signal losses mentioned above would probably
preclude being able to see meteor echoes.

While I know that the new phased array antennae have the ability to point
the beam in almost any desired direction, I think that John is right in
that these systems are more or less limited to monitoring the troposphere,
with an upper limit of about 12-15 km altitude.

3.  The digital signal processing utilized by these radars filters out
nearly all but the desired signals.  Aircraft, ground clutter, and the like
are all discarded (as much as possible), and only those objects which have
the desired signal  and velocity component are passed.  Even if a meteor
echo were received, I doubt that it would pass through the processor.


However, do take all of the above with a great big grain of salt, since I
have not worked with one of these radars.  The last actual surface radarI
got to take apart and play with was an "ancient" Navy AN/SPS-10, using some
very outdated technology.

Take care, everyone,

     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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