Observations of long-wavelength (λ > 30 m) radio radiation in space are reported and analyzed in the framework of the terrestrial environnement.
Measurements at low altitudes (~ 300 km) at the frequencies of 4.0 and 7.0 MHz have revealed the existence of very high radio noise levels during the night and on certain occasions during the day. These strong signals were at least 50 db higher than the expected cosmic background and are attributed to man-made and atmospheric radio noise.
Measurements at high altitudes (3000–11000 km) at the frequencies of 2.2 and 0.7 MHz have produced a flux value at 2.2 MHz in agreement with the expected cosmic radio background, but the flux value obtained at 0.7 MHz is approximately 15 db higher than the anticipated flux from cosmic sources. Harmonic gyroradiation from the artificial and the outer Van Allen belts might be the cause of the high radio flux observed at 0.7 MHz.