314 



REFRACTION AND REFRACTIVE INDEX MODELS 



1,000 

 700 

 500 



N 



RH = 100% 

 RH = 67 % 



RH = 33% 



RH =0% (DRY) 



TROPOSPHERE 



STRATOSPHERE 



W(h),RH=IOO% 



W(h),RH = 67 % 

 W(h),RH= 33% 



4 6 8 10 12 



H,gpkm 



Figure 8.2. N distribution for the I.C.A.O. standard atmosphere. 



14 



8.1.3. Properties of the Dry and Wet Term Scale Heights 



The average values of D and W versus height were determined for 

 22 U.S. radiosonde stations located about the country. The data used 

 were the published values of mean pressures, temperatures, and humidities 

 for the United States [9] which may be converted into mean values of the 

 refractive index with negligible error [10]. The method of least squares 

 was then used to determine the scale heights of the wet term, H^, and of 

 the dry term, Hd. Examination of these scale heights did not reveal any 

 simple method of predicting their geographic and seasonal behavior, other 

 than simply to map them. Such maps were prepared for the United States 



