(meteorobs) RE: A naive question

[weryk]

On Wed, 2007-30-05 at 08:27 -0400, drobnock wrote:
> Early meteor back/forward scatter work was started in lower VHF
> frequencies. At one time it was discussed that frequencies of 10/11
> metre were in the VHF range --very high frequency. Interesting
> electromagnetic frequencies in the 29-30 to 50 mHz range can be
> reflected. Early radar work was in this range.

So is some current back scatter work -- for example, the SKiYMET line of
meteor radar systems.

You use VHF frequencies when you want to backscatter off underdense
meteor trails.  If your wavelength is too small, you'll get destructive
interference from different points in the trail (because of the initial
trail radius) which attenuates your signal.

29 MHz would give you an underdense echo height distribution centred
around 90 km.

When using FM frequencies, you're only seeing overdense echoes (which is
when the electron line density reaches a certain value).

  Rob Weryk