DIELECTRIC CONSTANT, ABSORPTION AND SCATTERING 283 
10 
TOTAL K- BAND ATTENUATION 
« 4 uM 
TOTAL X-BAND ATTENUATION K72.40 0e/k 
X~, * 0.728 08/KM as 
<,/P = 0106 08/KM/MM/HR 
3 o< , (2.5)/p (2.5) #0,102 08/KM/MM/HR os 
ZB 3x00, osx/p * 03521 08/KM/MM/HR 
Ax (2.5)/p (2.5» 0.0332 08/KM/MM/HR 
g 
S 
§ & 
ATTENUATION IN OB PER Kil 
NUMBER OF 
° — — ° 
Q05 O10 0.15 020 0.25 0.30 035 0.40 
DIAMETER OF DROPS IN CM 
Ficurs 10. Drop size distribution and attenuation in 
._ a 22.6-mm per hr rain. Unlabeled curve represents Nx 
values; number of raindrops per cu m= Nx. 
hour rain are plotted. It is seen that the numerous 
smaller drops hardly contribute to the attenuation, 
which is caused mostly by the fewer larger drops and 
has a maximum around the 2.5-mm drops. 
In Table 9 is given the total attenuation (decibels 
per kilometer) in the wavelength range 1.25 to 100 
em in different rains of precipitation rates ranging 
from 2.46 to 43.1 mm per hour corresponding to 
given distributions. In Figure 11 are plotted some 
4 
ee 
to) 10 20 30 40 50 60 70 100 
AIN CM 
Ficure 11. Attenuation in rains of known drop size 
distribution as a function of the wavelength. The 
abscissa gives the wavelength, i, in centimeters. The 
ordinate scale gives logis a, where the attenuation con- 
stant, a, is expressed in decibels per kilometer. The 
letters on the curves refer to the drop size distributions 
given in Table 7. 
ATTENUATION IN DB PER Ki 
° 5 10 IS 20 25 30 35 40 45 
PRECIPITATION RATE INMM PER HR 
Ficure 12. (1) Computed K-band attenuation based 
on experimental drop size distributions. (2) Theoretical 
upper limit. «/p=0.16 db/km/mm/hr. t=18 C. 
curves showing, for a few rains, the variation of the 
total attenuation factor as a function of the wave- 
length. The dashed portions of these curves join the 
points previously computed,” the calculations start- 
ing at A = 5 em. 
Figures 12, 13, and 14 represent, at three typical 
wavelengths, the total attenuations in different rains. 
The results of the calculation are represented by the 
eS ee are 
[eS ee 
1.8 
1.6 
0.8 
0.6 
ATTENUATION IN OB PER KM 
° $ 10 6 2 25 30 35 #40 «45 
PRECIPITATION RATE IN MM PERHR 
Ficure 13. (1) Computed X-band attenuation based 
on experimental drop size distributions. (2) Theoretical 
upper limit. a/p=0.045 db/km/mm/hr. i=18 C. 
175 
ATTENUATION IN 10°“ DB PER KM 
o 5 10 15 20 2 30 35 40 45 # 50 
PREGIPITATION RATE IN MM PER HR 
Ficure 14. (1) Computed S-band attenuations based on 
experimental drop size distributions in different rains. 
(2) Theoretical upper limit of a/p, attenuation per unit 
rate of precipitation, is 6.10-4db/km/mm/hr. t=18 C. 
