(meteorobs) Observability function O.F - newbie question

mark ford markf at ssl.gb.com
Mon May 16 04:48:38 EDT 2005



David,

Thank you for that, comments and papers noted, I shall go digging.

I am also thinking that perhaps some kind of 'ping integration' might be
more effective rather than just peak amplitude detection. This would
involve sampling each 'ping' and performing an integration on all the
signal components to achieve if you like, an 'energy value'. I am sure
there is some clever mathematics potential there somewhere, (but as I
have trouble adding up my shopping list)  it may require some careful
study :) , I will report back if I get somewhere!

Thanks & Best Regards,
Mark Ford




-----Original Message-----
From: David Entwistle [mailto:david.entwistle at dial.pipex.com] 
Sent: Friday, May 13, 2005 5:20 PM
To: Global Meteor Observing Forum
Subject: Re: (meteorobs) Observability function O.F - newbie question

In message <6CE3EEEFE92F4B4085B0E086B2941B312450F0 at s-southern01.s-
southern.com>, mark ford <markf at ssl.gb.com> writes
>
>a)       How does one work this O.F correction curve out?

Mark,

It's an interesting and difficult question.

As Frans says, Professor Dr Oleg Belkovich will be attending the IMC in
September 2005. He'll be presenting a five day tutorial on the theory of
radio meteor observations. that could be an ideal time to get the full
answer.

I don't know the full answer to your questions myself, but there are
some excellent references on the IMO radio section bibliography web
page.

http://www.imo.net/radio/bibliography.html

In particular, that list includes Planet Space Science Vol 38, pp.
55-66, 1990. 'Oblique Scattering of Radio Waves from Meteor Trains:
Theory', by W Jones and J. Jones. This article investigates the general
application of Maxwell's equations to the forward scattering of radio
waves from a meteor train. Unfortunately, for me, there aren't any
diagrams and the mathematics is beyond me.

There is an article, which I found easier to understand. It's from The
Canadian Journal of Physics Vol 33, September 1955, Number 9 (page 493
to 503): 'Diurnal Variations in the Number of Shower Meteors Detected by
the Forward Scattering of Radio Waves', C. O. Hines. It's mentioned on
the D.M.S. web site and appears to be a clear and complete treatment of
the subject. The mathematics is demanding (for me), but understandable.

I also found ITU Recommendation ITU-R P843-1 'Communication by Meteor
Burst Propagation' to be most informative. It's intended as a guide for
designers of meteor-burst communication systems, but includes a thorough
analysis of the mechanism.

If you have any trouble getting hold of any of these articles, drop me
an email and I'll see what I can do.

>
>b)       Could I vary the amplifier gain on the radio receiver inline
>with the O.F. (for example using PC software to control the gain with
an
>electronic attenuator on a continuous basis), to fool the receiver into
>seeing a constant uniform 'signal strength' for a given radiant(s)?
>rather than post processing the information. (It actually would only
>need to be a PC audio volume control that varies with the O.F)
>

I think post processing may be a more successful option, as I'm not sure
that a volume control arrangement would work, but it could be worth
experimenting. The OF will be a function of many things, which will
include the following:

i) The altitude of the radiant above the horizon of an imaginary
observer located at the mid-point of the Tx - Rx path. This will
actually affect the number of meteors entering the observer's sky - in
the same way it would for a visual observer.

ii) The geometry of the radiant, with respect to the transmitter and
receiver will affect the strength and duration of each reflection.

iii) The geometry of the radiant, with respect to the polarisation of
the transmitter's aerial and the receiver's aerial.

So we can expect the number, the strength and the duration of the
reflections to change as the radiant moves across the observer's sky.
There may be a complex relationship to the volume of the pings heard,
but it will not be a simple one.

>
>This assumes that 'worst case' is when a meteor trail is 'end on' to
the
>receiver. Presumably you would still get a signal but it would be much
>reduced in intensity? 
>

Again, dependant on the mode that your receiver is operating in, there
will be a relationship between signal-strength and audio volume, but it
will not be a simple linear one. For example, with USB mode, it is the
signal-to-noise ratio of the audio output which increases, with
increasing signal strength, not the audio level. You hear a ping as the
energy in the receiver's audio output becomes concentrated in a narrow
band, rather than spread across the whole audio spectrum. It depends how
you measure it, but the audio output level doesn't necessarily increase
when you hear a ping.

> (and obviously sporadic's will always have random directions so the
>true numbers /sizes will not be counted).
>

-- 
David Entwistle
---
Mailing list meteorobs
meteorobs at meteorobs.org
http://lists.meteorobs.org/mailman/listinfo/meteorobs




More information about the Meteorobs mailing list