THE HEIGHT DISTRIBUTION OF RADIO METEORS - COMPARISON OF OBSERVATIONS AT DIFFERENT FREQUENCIES ON THE BASIS OF STANDARD ECHO THEORY

A comparison is made between the observed height distributions of underdense radio meteor echoes measured at frequencies of 2, 6, 26 and 54 MHz and a simple model based on standard theory. This theory takes account of the initial radius of the train, the finite formation time due to the meteor velocity, and diffusion in the time between radar sweeps. The main features of the measured VHF (26 and 54 MHz) height distributions are predicted by this model, with peaks below 100 km and few meteors detected above 105 km. The main features of the measured HF (2 and 6 MHz) distributions are also successfully predicted, with peaks at approximately 105 km. The model indicates few 6 MHz echoes from above 115 km, in line with the observational data, although for the data used there is an instrumental cut-off just above this height. It is suggested that even at 2 MHz perhaps 50% of all meteor trains above 105 km remain undetected. A comparison of the model and the measured 2 MHz distribution, which displays many meteors to at least 130 km, reveals that the true height distribution continues to rise above 105 km and would peak above 110 km were it not for the limited detectability of such high altitude meteors, even at such low frequencies.