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A resolution volume is shown in Fig. 6.10, and is approximated by
π
---
θ
a
θ
e
R
2
c
τ
V
W
≈
(6.32)
where
θ
a
,
θ
e
τ
are, respectively, the antenna azimuth and elevation beamwidths
in radians,
is the pulsewidth in seconds,
c
is speed of light, and
R
is range.
c
τ
2
-----
R
θ
a
θ
e
Figure 6.10. Definition of a resolution volume.
Consider a propagation medium with an index of refraction
m
. The
ith
rain
droplet RCS approximation in this medium is
π
5
λ
4
-----
K
2
D
i
6
σ
i
≈
(6.33)
where
m
2
2
1
K
2
=
----------------
(6.34)
m
2
+
2
and
D
i
is the
ith
droplet diameter. For example, temperatures between
32°
F
and
68°
F
yield
0.93
π
5
λ
4
-----
D
i
6
σ
i
≈
(6.35)
and for ice Eq. (6.33) can be approximated by
0.2
π
5
λ
4
-----
D
i
6
σ
i
≈
(6.36)
Substituting Eq. (6.33) into Eq. (6.30) yields
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