Frequency dependence of Doppler shift for type III coherent radar echoes

Coherent echoes were observed simultaneously from the same scattering region using two bistatic radars operating at 50 MHz and 60 MHz. The data were searched for the occurrence of type III echoes. If type III echoes are caused by ion-cyclotron waves, one would expect the Doppler shift to be nearly equal to the ion-cyclotron frequency in the scattering region for both radars, and hence to be equal. On the other hand, if type III echoes are just low velocity type I echoes, then the phase velocity should be the same, and hence the Doppler frequency shift should be scaled according to observation frequency. The results of this experiment indicate that the two radar spectra seem to scale according to frequency as would be expected for scatterers with a similar phase velocity at the two radar wavelengths.