Radar Propagation Medium

This analysis presented in this chapter accounts for the effects of the earth's atmosphere and the effects of the earth's surface on the radar waves. Despite the fact that “free space analysis” may be adequate to provide a general understanding of radar systems, it is only an approximation. In order to accurately predict radar performance, one must modify free space analysis to include the effects of the earth and its atmosphere. These modifications account for ground reflections from the surface of the earth, diffraction of electromagnetic waves, bending or refraction of radar waves due to the earth's atmosphere, Doppler errors, rotation of the polarization plane, time delays, dispersion effects, and attenuation or absorption of radar energy by the gases constituting the atmosphere. The earth's impact on the radar equation manifests itself by introducing an additional power term in the radar equation. This term is referred to as the pattern propagation factor.