66 TROPOSPHERIC REFRACTION 



Table 3.3. Table of the constant Ce for the CRPL exponential radio refractivity 



atmospheres 



with the Rocket Panel and ARDC data. The exponential reference at- 

 mosphere is also shown on figure 3.5 for N s = 313, the average value of 

 the United States. The exponential reference atmosphere appears to be 

 a reasonable single line representation of A'^ throughout the height interval 

 shown. The differences between the various models becomes more 

 apparent by examining their agreement with observed N profiles over the 

 first 10 km as in figure 3.6. 



The reference and exponential reference atmospheres are given for the 

 N profiles corresponding to near-maximum N s (Lake Charles, La.) and 

 near minimum-at-sea-level Ns conditions (Caribou, Me.). The two 

 reference atmospheres were determined solely from the N s values of each 

 profile. Several observations can be made of these data. First, the 4/3 

 earth model closely represents the slope of the minimal N s profile over 

 the first kilometer, but then decreases too rapidly with height. Note, 

 however, that the 4/3 earth model with its constant decay of 39.2 N units 

 per kilometer would be a very poor representation of the maximum pro- 

 file which decreases over 66 N units in the first kilometer. The exponen- 

 tial reference atmosphere is in good agreement with the initial N distribu- 

 tion but tends to give values systematically low above approximately 

 3 km. At first glance, the exponential reference atmosphere does not 

 appear to be as good a representation of the two observed profiles as the 

 reference atmosphere, particularly above approximately 5 km. Subse- 

 quent analysis of the refraction obtained from the two model atmospheres 

 will show that this systematic disagreement of the exponential reference 

 atmosphere in the 5- to 20-km interval is a minor defect of the model 

 compared to its closer agreement with observed N distributions over the 

 first 1 to 3 km. This is particularly true for the higher values of N s such 

 as that for Lake Charles. 



The above models are more in agreement with long-term mean N pro- 

 files than is the 4/3 earth model. The application at hand would aid in 

 deciding which of the reference atmospheres would be most useful. To 



