Re: (meteorobs) meteor detection in AM SW band

These statements regarding the transparency of our atmosphere to RF are a substantial oversimplification, and hence not really accurate. The transparency of our atmosphere (actually the ionospheric layer) to vertically incident waves is given by the parameter fc (critical frequency). Frequencies above fc penetrate through to space, while those below are reflected back to earth. fc varies tremendously with time of day, geographical location, season, 27-day and 11-year solar cycle. It can be as high as 50-60Mhz (6 meters) during daytime 11-year solar maximum, and as low as 1 Mhz (300 meters) during night at solar minimum. In addition, the transparency is a function of angle of incidence, which along with fc, determines the MUF (maximum usable frequency) for HF radio transmissions. MUF more closely tracks the frequencies of interest for any meteor scatter work, since it deals with propagation at the typical low incidence angles for terrestrial signals. MUF varies from a high of around 70Mhz to a low around 2-3Mhz.

The science of ionospheric radio wave propagation is complex, with sophisticated models and software available to track these parameters and frequencies, in near real time. Anyone interested in using these range of frequencies for meteor scatter should be aware of these issues, and not rely solely on oversimplified and generalized statements as presented here by CR Kitchen.

Mike Linnolt

--- drobnock2 <drobnock@penn.com> wrote:

>  See -- C. R. Kitchen, "Astrophysical Techniques,"
> Adam Hilger, Ltd., 
> 1984 revised 1991.
> Kitchen  makes the statement that in radio astronomy
> - scatter radio 
> is within this astronomy  - the sky is transparent
> for electromagnetic 
> radio between 10mm and 10 meters (microwave to 25
> mHz). He further 
> states that electromagnetic radiation greater than
> 50 meters 
> (transmitted from earth) fails to penetrate the
> atmosphere and is 
> reflected back into the atmosphere.
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