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Re: (meteorobs) Radio meteors can one tell magnitude?

In message <4086A528.B1C73FE7@eastlinkdot ca>, Michael Boschat
<mboschat@eastlinkdot ca> writes
>Hi:
>
> I'm not sure how to answer this question put to me but another observer asked
>if listening to radio meteors if it was possible to determine their magnitude?
>Example a -1 meteor would it be louder or fainter in volume? 
>

Unfortunately I don't think there's a simple answer to your question,
but I'll have a go.

There's an International Telecommunications Union recommendation (ITU-R
P.843-1 'Communication by Meteor Burst Propagation'), which attempts to
provide a model for predicting the received signal strength from meteor
burst propagation. The model proposed is relatively complex and limits
itself to considering reflections from underdense trails, but may be
summarised as follows. 

The received signal strength is proportional to the product of the
following:

 Transmitter power
 Transmit and receiver antenna gain
 Wavelength squared
 Various losses, including ionospheric absorption
 Echoing area of the trail (see below)

The received signal strength is inversely proportional the product of
the following

 The square of the distance between the transmitter and the meteor.
 The square of the distance between the meteor and the receiver.

Most of these factors would be fixed for any given radio-meteor
detector. The main variable is the echoing area of the trail. This would
tend to increase with increasing optical magnitude, but there are
complications. In the recommendation, the echoing area of the trail is
suggested to be proportional to the product of the following variables:

 The electron line density squared
 Effective length of the portion of the trail providing reflections,
which interfere constructively, at the observer's location, squared.
 The square of the sine of the angle between the incident and reflected
wave (actually the electrical vector)...

It is this last variable, which results in a radio meteor system having
an increased ability to detect reflections from particular areas of the
sky - the so called 'hot spots'. 

So, I'd suggest that optically bright meteors would tend to produce
stronger echoes with a longer duration - leaving trails of increased
electron density and increased echoing area, but the geometry of the
reflection has a very pronounced influence on the strength of the echo
too. In general, the influence of the geometry would prevent the
estimation of magnitude from received signal strength. However, if you
knew the geometry, you could probably have a good stab at the optical
magnitude. Additionally, the relationship between the volume of the
radio's audio output and the received signal strength will also depend
on the type of detection employed in the receiver (CW, SSB, AM etc.)...
  
-- 
David Entwistle

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