the amplitudes a n and b n are too complicated to be 

 reproduced here. Their numerical evaluation for 

 spherical drops of given size and temperature is 



20 30 



40 50 60 70 

 AIN CM 



Figure 3. Attenuation in rains of known drop-size dis- 

 tribution as a function of the wavelength X in centi- 

 meters. The ordinate scale gives logio oi, where the 

 attenuation constant a is expressed in decibels per 

 kilometer. The letters on the curves refer to the drop 

 size distributions given in Table 1 1 . 



quite laborious except for small values of the para- 

 meter irD/\. They involve Bessel and Hankel func- 

 tions of half-integer order of the parameter xD/X. 



A series of experimental results are given in Table 

 13. These results are to be regarded as maximum 

 attenuation values. 



If these results are compared with those of Table 

 10 and Figure 2 one sees that, in view of the uncer- 

 tainty in the temperature of the raindrops and their 

 size distribution, the agreement between theoretical 



