Ionospheric effects encountered by systems operating in the frequency bands above HF are generally associated with earth-space propagation. A treatment of these effects appears in an excellent, but dated, pair of documents by Lawrence et al.  and by Flock , Goodman  treats the subject with an emphasis on applications. The reader should consult ITU-R documents for more current information [ITU-R, 1996]. It must be remembered that all of the significant radiowave parameters such as signal amplitude, wave polarization, and wave phase vary as the radiowave traverses the ionospheric medium, and the exiting wave retains a "memory" of the integrated variations. Many of the system impairments, with the exception of scattering and scintillation effects that depend upon detailed distributions, are directly related to the integrated electron density, often referred to as the electron content (EC) that is encountered by the radiowave. This is the integral of the electron density from an earth terminal to the satellite platform or target. In general, this is a slant value of the electron content, unless the path is along an earth radial. In practice, analysts measure the Slant Electron Content (i.e., EC), and then compute the Total Electron Content (i.e., TEC), which references the measured EC to the vertical. Table 4-8 exhibits the relationship between the EC and the effects of interest, viz., Faraday rotation, group-path-delay, phase advance, ionospheric Doppler, and signal dispersion. Estimated maxima for effects is provided in Table 4-7.
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