Ionospheric effects on the Doppler frequency shift in SARSAT propagation / by D.B. Muldrew and H.G. James.: Co24-3/7-1313-1978E-PDF

"The Doppler frequency shift of signals propagating from an Emergency Locator Transmitter (ELT) on a downed aircraft up to a transponder on a search and rescue satellite (SARSAT) and down to a central station is affected by the ionosphere. In this report ionospheric effects are estimated for a proof-of-concept SARSAT experiment using the AMSAT OSCAR-6 satellite. In this case, the down link is at 30 MHz and the daytime ionosphere with no horizontal gradients in electron density can change the Doppler frequency by a few hertz. Horizontal gradients of electron density can have more effect on the Doppler frequency than the vertical distribution of density since the negative vertical density gradient in the topside ionosphere tends to compensate the Doppler effect due to the positive gradient in the bottomside. In the late afternoon, evening and nighttime, large east-west troughs in the density distribution exist which can produce shifts of a few tens of hertz at 30 MHz. The Doppler frequency shift due to the ionosphere varies approximately inversely as the frequency. The results obtained here can be applied to the definition of an operational SARSAT system"--Abstract, page 1.

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