Progress On Aids To Interpretation

To correctly interpret radar data it is important to incorporate realistic physical effects. Here mention is made of three recent aids in the area.

To gain absolute meteoroid mass calibration and flux calibration, account needs to be taken of the attenuating effect of the meteoric plasma column radius at formation. Using simultaneous multiple wavelength records of Leonid echoes, Campbell [15] has measured train formation cross-sections as a function of height: this 'height-ceiling' effect can have gross effects on estimates of meteor fluxes and masses.

At heights in the atmosphere where the electron gyro frequency exceeds the electron-neutral collision frequency, the rate at which a meteor train diffuses depends on the orientation of the train and radar line of sight to the local geomagnetic field. Elford and Elford [16] have provided numerical values showing how the effective diffusion can be inhibited: small high-speed meteoroids inaccessible to many radars because of the rapid diffusion of their plasma column can have extended echo life-times depending in the relevant geometry.

Though radio wave absorption will be negligible at the frequencies utilised by many meteor radars, it is expected that Faraday rotation produced by the day-time lower E-region ionization situated below the reflection point can be significant. Many meteor radars employ linearly polarised antennas so that polarisation rotation can lead to effective signal attenuation [17].

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