274 ATTENUATION OF RADIO WAVES 



Table 7.2. Values used in the calculation of atmospheric absorption 



*p is water vapor density in g/m^ 



than that of the predicted amount, particularly above 50,000 Mc/s [13]. 

 These observed discrepancies have little effect upon the present study, 

 which is confined to frequencies less than 50 Gc/s. The results of the 

 present study, for the frequency range 100 to 50,000 Mc/s, agree with 

 those reached by Tolbert and Straiton [14] in their field experiments at 

 Cheyenne Mountain and Pikes Peak, Colo., at altitudes of 14,000 ft. 



The above approach represents that presented by Bean and Abbott 

 [3]. The following treatment was given by Gunn and East [15] and 

 based on Van Vleck's two papers [4, 5]. This latter presentation is only 

 valid when single line absorption with no appreciable overlap from 

 adjacent lines is considered. 



By taking into account the temperature and pressure dependence of 

 the line widths, it is seen that for a given quantity of water vapor, the 

 attenuation is proportional to 



P- and T- exp (- f ) , 



at the resonance line, to 



P and T~' exp (- ^) 



at the sides of the curve, and to P and T"3/2 ^g][ away from resonance. 

 In applying the above considerations to absorption approximations it 

 also must be remembered that for a given relative humidity, the density 

 will vary considerably with temperature. Table 7.3 shows attenuation 

 by water vapor at various temperatures and wavelengths. 



