Handbook of Propagation Effects for Vehicular and ... - Courses

9-4
Propagation Effects for Vehicular and Personal Mobile Satellite Systems
ho = H 4 . (9-6)
The significant wave height is the average height of waves corresponding to the highest
one-third of the actual waves that pass a fixed point. When the sea is rough, the
incoherent and coherent components of the scattered powers, PI, PC may be expressed in
terms of the coefficients ηI ( u)
and ηC ( u)
defined such that
and
P ( u) = η ( u) P
2 (9-7)
I I CO
P ( u) = η ( u) P
2
C C CO
, (9-8)
where PCO is given by (9-1). The mean total power of the reflected waves is thus given
by
Pr CO
C I
2
2 2
2
( u)
= η ( u)
P with η = η ( u)
+ η ( u)
. (9-9)
The coherent component η C is related to the roughness parameter u by the relation
[Beckmann and Spizzichino, 1963],
η C
2
= exp( −u
/ 2 ) . (9-10)
For u > 1, Miller et al. [1984] showed the results to be consistent with the measurements
of Beard [1961] (for u up to 3) where η C is defined by
2 2
ηC = −u
Io u
exp( / 2) ( / 2 )
(9-11)
and where I0 is the zero-order modified Bessel function. Karasawa and Shiokawa
demonstrated from their measurements at 1.5 GHz using right-handed circular
polarization that
η
η
2
2
≈ η
≈ η
2
C
2
I
+ η
≈ 1
2
I
≈ 1
for
for
0 ≤ u < 2
. (9-12)
2 ≤ u ≤ 10
Combining (9-12) with (9-10) or (9-11) enables η I 2 to be explicitly expressed by
or
2
2
η = 1−
exp( −u
)
(9-13)
I
2
I
[ ] 2 2
2
exp( − / 2)
I ( / 2)
η = 1 −
u . (9-14)
u o