Relativistic effects in radar detection of ionization fronts produced by ultra-high energy cosmic rays

We revisit the radar echo technique as an approach to detect ultra-high energy cosmic rays (UHECR). The UHECR extensive air showers generate disk-like ionization fronts propagating with a relativistic velocity and creating fast decaying plasma. We study the reflection of a radio wave, such as the one from a radar transmitter or commercial radio and TV station, from the relativistic ionization front. The reflected wave will be frequency upshifted due to the relativistic Doppler effect and propagate almost normally to the front due to relativistic aberration. The amplitude of the reflected wave depends strongly on the front velocity and parameters (density, collision frequency) of the plasma behind the front. We develop a theory that allows one to find the reflected wave. Using this theory and typical parameters of extensive air showers, we discuss the feasibility of UHECR detection. © 2010 Elsevier B.V. All rights reserved

The no-reflection regime of radar detection of cosmic ray air showers

© 2015 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. The ionization front of a cosmic ray air shower propagates in the atmosphere with almost the speed of light in vacuum, i.e., faster than a radio wave in the air. There can be no reflection of a radar signal from such a front. Instead, an additional transmitted wave, which travels behind the front in the backward direction, is generated. We study the frequencies, propagation directions, and amplitudes for the waves excited at the front and discuss their use for radar detection of air showers

Prospects for radar detection of cosmic ray air showers with medium-frequency radio waves

We show that the highly relativistic motion of an extensive air shower allows one to increase the wavelength of the radar signal above its transverse size without giving rise to signal scattering. This increases the efficiency of detection due to an increase in the reflection from the shower and a lower level of sky noise in the frequency range of the reflected signal. © IOP Publishing and Deutsche Physikalische Gesellschaft