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where Z: Dt is the sum of the 6th power of the diameter of the particle within a unit
vol
of volurns. Z = Z: D; is oiian called the 'reflectivity factor'.
It has been f%nd that the backscattered signal varies from one reflected pulse to the
next. This is caused by movements of the particles with respect to one another. Therefore,
in practice the averaged power per unit of area Wb of a number of reflected pulses
is detected.
5. THE RADAR EQUATION
Until now the averaged reflected power per unit area Wb intercepted by the antenna
has been described as a function of Wo, the power per unit of area intercepted by the
scattering precipitation particles.
The power, Pt, transmitted by the radar set is concentrated in a narrow beam of width
0. Particles at a range r along the axis of this beam will receive a power per unit of area
W, , which is proportional to P,/O (see Fig. 3).
Obviously, 0 -- 8' r2. So we obtain, if the radar beam is entirely filled with precipitation
particles:
wo - ~ ~ / t ~ ~ r ~ (6)
Substituting (6) in (S), we can write:
The total average power, Fr, intercepted by the antenna is equal to qt, . A,, where Ae
is the effective area of the antenna. It is found that A, = 4 A (A is the actual area of the
antenna), if the antenna is circular.