Page 167 - Fundamentals of Radar Signal Processing

FIGURE 2.29 Illustration of two scattering phenomena which violate the one-to-
one mapping of time to range: (a) multipath, (b) multiple bounce.

Figure 2.29b illustrates the effect of multiple bounce echoes in a situation
involving two scatterers. A portion of the energy reflected from the more distant
scatterer bounces off the nearer scatterer, then reflects a second time off the
distant scatterer and returns to the radar. Obviously additional multiple bounces

are also possible. For the situation sketched, three apparent echoes will again
result, with the third due to a phantom scatterer 2ΔR behind the second actual
scatterer. As with multipath, the amplitude of multiple bounce echoes often falls
off rapidly, and the same considerations of in- and out-of-phase superposition
apply.
These possible differences in the measured and actual reflectivity

distributions do not mean that range profile measurements are not useful. They
do mean that in situations where significant multipath or multiple bounce
phenomena are possible, the range profiles must be interpreted with care.

2.8 Spectral Model

There is one more interpretation of the received radar signal that proves useful
in subsequent chapters. The preceding two sections have emphasized linear
filtering models of the spatial reflectivity distribution as observed through the

received complex baseband signals. However, it was pointed out previously
that radar cross section is a function of, among many other things, the radar
frequency. Thus, it is useful to investigate the significance of the radar