Propagation Effects Handbook for Satellite Systems - DESCANSO ...

values of water vapor densities >12 g/m3, has been proposed by
Gibbons (1986) and provisionally accepted by the CCIR (1988)~
Yw =
[ 0.050 + o.oo21p +
w
8.9
(f - 22.2) 2
‘ ( f - 325.4) 2
+ 26.3
for T = 15°C and f c 350 GHz.
3.6 10.6
1
+ 8.5 ‘(f- 183.3) 2
-I- 9.0
/2 pw 10-4 dB/km
(6.2-6)
Gibbons finds Eq. (6.2-6) to be valid within about * 15% over
the range of Pw from O to 50 g/m3. However, in applying Eq. (6.2-6)
with water vapor densities greater than 12 g/m3 it is important to
remember that the water vapor density may not exceed the saturation
value p~ at the temperature considered.
expressed as (Gibbons~ 1986)~
This saturation value may be
P. = 17.4(*) 6
where T is the temperature in ‘K.
29502
10-y
[
1
1 0
g/rn3 (6.2-7)
For temperatures in the range -20”C to +40°C Gibbons proposes a
temperature dependence of -1.0% per ‘C for dry air in the window
regions between absorption lines and -0.6% per ‘C for water vaPor.
The correction factors are therefore
Y. = YO(15 OC)[l - O.O1(TO -
15)]
(6.2-8)
Y w = YW(15 oc)[l - 0.006(T, - 15)] (6.2-9)
where To is the surface temperature in ‘C.
6-14