Use of Z-Mode Propagation for observing Cosmic Radio Noise from Earth Satellites

Abstract

SATELLITES for the observation of cosmic radio noise are being prepared by several groups in the world in order to study the spectrum and the pattern of sky brightness at wave frequencies less than the ionospheric critical frequency, which normally does not go much below 2 Mc./s. Some of these satellites, although planned to orbit above the height of maximum ionization density, will still be immersed in a considerable amount of ionization. In these circumstances the refraction by the medium will limit the region of the sky observed to a quasi-elliptical area centred on the zenith and defined by Snell's Law. Restriction of the observable part of the sky in this way provides in principle a means of increasing the angular resolution of the antenna. However, except when the wave frequency is almost equal to the local plasma frequency, the angular size of the observed area is large. It is also variable, and the proper interpretation of the effect of refraction requires a knowledge of the ionization density at all points on the satellite orbit.