ABSTRACT
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 and is symbolically denoted by . The propagation factor can actually introduce constructive as well as destructive interference onto the SNR depending on the radar frequency and the geometry under consideration. In general, the pattern propagation factor is defined as
where is the electric field in the medium and is the free space electric field. In this case, the radar equation is now given by
8.2. Earth’s Atmosphere The earth’s atmosphere compromises several layers, as illustrated in Fig. 8.1. The first layer,
which extends in altitude to about 30Km, is known as the troposphere. Electromagnetic waves refract (bend downward) as they travel in the troposphere. The troposphere refractive effect is related to its dielectric constant, which is a function of the pressure, temperature, water vapor, and gaseous content. Additionally, due to gases and water vapor in the atmosphere, radar energy suffers a loss. This loss is known as the atmospheric attenuation. Atmospheric attenua-
Fp
Fp E E0= E E0
SNR PtG
22 4 3kT0BFLR4
----------------------------------------Fp 4=
tion increases significantly in the presence of rain, fog, dust, and clouds. The region above the troposphere (altitude from 30 to 85Km) behaves like free space, and thus little refraction occurs in this region. This region is known as the interference zone.
