SCATTERING AND ABSORPTION OF MICROWAVES 49 
Taste 10. Attenuation in decibels per kilometer for different rates of precipitation of rain. Temperature 18 C, \ in em.?77 
Attenuation, db/km. 
P, 
mm/hr rA = 0.3 \ = 0.4 A= 0.5 A = 0.6 = 10 »X = 1.25 r.= 3.0 A = 3.2 A= 10 
‘ 0.25 0.305 0.230 0.160 0.106 0.637 0.0215 0.00224 0.0019 0.0000997 
1.25 1.15 0.929 0.720 0.549 0.228 0.136 0.0161 0.0117 0.000416 
2.5 1.98 1.66 1.34 1.08 0.492 0.298 0.0388 0.0317 0.000785 
12.5 6.72 6.04 5.36 4.72 2.73 1.77 0.285 0.238 0.00364 
25 11.3 10.4 9.49 8.59 5.47 3.72 0.656 0.555 0.00728 
50 19.2 17.9 16.6 15.3 10.7 7.67 1.46 1.26 0.0149 
100 33.3 31.1 29.0 27.0 20.0 15.3 3.24 2.80 0.0311 
150 46.0 43.7 40.5 37.9 28.8 22:3. 4.97 4.39 0.0481 
Tasie 11. Attenuation in rains of known drop size distribution and rate of fall (decibels per kilometer). 
Wavelength , em 
5 
mm/hr 1.25 3 8 10 15 Distribution 
2.46 1.93 10 4.92 10-2 4.24 10-3 1.23 10-3 7.34 1074 2.80 1074 A 
4.0 3.18 107 8.63 10-2 ele Oe? 2.04 10-3 1.19 1073 4.69 10-4 Cc 
6.0 6.15 107 1.92 10-4 1.25 107? 3.02 10-3 1.67 1073 5.84 1074 D 
15.2 2.12 6.13 107 5.91 1072 1.17 107? 5.68 1073 1.69 1073 E 
18.7 2.37 8.01 107 5.13 1052 LORS On 6.46 1073 1.85 1073 F 
22.6 2.40 7.28 107 5.29 107? 1-21 1057 6.96 10-3 2.2% 105% G 
34.3 4.51 1.28 1.12 107 2.02 1052 Le LOR 3.64 1073 H 
43.1 6.17 1.64 1.65 107 3.33 107-2 1.62 107? 4.96 1073 I 
Wavelength A, cm 
mm/hr 20 50 75 100 Distribution 
2.46 152g Ome 6.49 1075 2.33 1075 1.03 10-5 5:35 105° A 
4.0 2.53 1074 1.08 1074 3.88 107-5 2 Ome 9.75 10 Cc 
6.0 3.02 10-4 25 Om* 4.34 10-5 1.93 10-5 1.09 10-5 D 
15.2 7.85 1074 2.95 1054 9.23 1075 4.15 107-5 2.35 1075 E 
18.7 9.09 1074 3.60 1074 1.20 10-4 5.36 107-5 3.03 1075 F 
22.6 Li 105% 4.81 10-4 1.66 10-4 7.41 1075 4.19 10-5 G 
34.3 1.75 10-3 6.83 1074 2.24 1074 9°95" 105° 5.63 107-5 H 
43.1 2.29 1073 8.71 1074 2.78 1074 1.23 10>4 6.98 10-5 I 
dielectric properties of water, it seems important to 
evaluate the attenuation of rains whose drops are 
at temperatures different from those included in the 
preceding tables. Table 12 contains the necessary 
data relative to the changes of attenuation with 
temperature and is to be used primarily in eonnec- 
tion with Table 10. 
TABLE 12 
Rate of Correction factor 6 (T’) 
precipitation, A, Qs PS PSs PSs Ts 
mm/hr cm 0C 10C 18C 30C 40C 
0.25 0.5 0.85 0.95 1.0 1.02 0.99 
1.25 0.95 1.0 1.0 0.90 0.81 
3.2 1.21 1.10 1.0 0.79 0.55 
10.0 2.01 140 1.0 0.70 0.59 
2.5 0.5 0.87 0.95 1.0 1.03 1.01 
1.25 0.85 0.99 1.0 0.92 0.80 
3.2 0.82 1.01 1.0 0.82 0.64 
10.0 2.02 140 1.0 0.70 0.59 
12.5 0.5 0.90° 0.96 1.0 1.02 1.00 
1.25 0.83 0.96 1.0 0.93 0.81 
3.2 0.64 0.88 1.0 0.90 0.70 
10.0 2.03 1.40 1.0 0.70 0.59 
50 0.5 0.94 0.98 1.0 1.01 1.00 
1.25 0.84 0.95 1.0 0.95 0.83 
3.2 0.62 0.87 1.0 0.99 0.81 
10.0 2.01 140 1.0 0.70 0.58 
150 0.5 0.96 0.98 1.0 1.01 1.00 
1.25 0.86 0.96 1.0 0.97 0.87 
3.2 0.66 0.88 1.0 1.03 0.89 
2.00 140 1.0 0.70 0.58 
° 10 20 30 40 50 60 70 80 90 100 
AIN CM 
Figure 3. Attenuation in rains of known drop-size dis- 
tribution as a function of the wavelength \ in centi- 
meters. The ordinate scale gives logic a, where the 
attenuation constant @ is expressed in decibels per 
kilometer. The letters on the curves refer to the drop 
size distributions given in Table 11. 
