Ionospheric Doppler Shift

Ionospheric Doppler is given by the time rate of change of the ionospheric phase change times the quantity (l/2jt). In other words, simply divide Equation 4.4 by 2n. We then have the following:

This effect is not very significant if the transmission frequency is sufficiently high. For example, for a rapidly moving satellite, d/dt (EC) would be ~ order of the EC divided by ~ several minutes. We assume d/dt (EC) ~ A(EC)/At, where A(EC) and At are finite values. Taking A(EC) ~ 1017 electrons/m2 and At ~ 60 seconds, the ionospheric Doppler shift at 1.6 GHz is about 0.1 Hz. At 160 MHz, it is ~ 1 Hz, and at 16 MHz, it is ~ 10 Hz under the stated conditions. Figure 4-13 shows the free space and ionospheric Doppler for a satellite transmitting at 20 MHz.

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Mountain Standard Time

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Mountain Standard Time

Figure 4-13: Computed Doppler, including the ionospheric component, for a rapidly moving LEO satellite. The transmission frequency is 20 MHz. From Lawrence et al., [1964].

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