Transmission of Electromagnetic Waves Through Normal and Disturbed Ionospheres
Calculations of expected total transmission attenuation are presented for earth-to-satellite paths in an ambient and a nominally disturbed ionosphere under both day and night conditions for frequencies from 10 to the minus 3rd power to 10 to the 10th power Hz. Height profiles of attenuation are given for frequencies from 1 Hz to 100 kHz. Results show that, under ambient conditions and for quasi-longitudinal propagation, the ionosphere is relatively transparent to electromagnetic waves having frequencies lower than about 10 kHz. For some classes of artificially or naturally disturbed ionospheres, frequencies lower than a few tens of Hz must be used if less than 30-dB transmission loss is to be avoided. Another possible scheme would be to use several satellites configured so as to maximize the probability that at least one satellite is transmitting under undisturbed ionospheric conditions. Part of the propagation path is thus assumed to be in the earth's ionosphere cavity.