70 



TROPOSPHERIC REFRACTION 



en 



< 



< 

 CC 



T at 70 km 

 Mean profiles: 15.12 mrad 

 Mean exp. ref.; 15.23 mrad 

 4/3 earth ; 30.25 mrad 



6 8 10 12 14 



h-hs IN KILOMETERS 



Figure 3.9. Bending versus height. 



16 



20 



Further, the bending in the 4/3 earth atmosphere is compared with 

 that in the exponential reference atmosphere in figure 3.9. The bending 

 in an "average" atmosphere is also given. This average atmosphere is 

 a composite of the 5-year mean profiles for both summer and winter at 

 the 11 U.S. radiosonde stations enumerated in the following paragraph, 

 and was used as a readily available measure of average conditions. The 

 important point made by figure 3.9 is that the 4/3 earth model is sys- 

 tematically in disagreement with average bending; at low heights it gives 

 too little bending, while at high altitudes it gives too much bending. The 

 exponential reference atmosphere does not appear to be systematically 

 biased, and deviates less than 5 percent from the average atmosphere. 

 It is significant that the exponential reference and the average atmosphere 

 are in essential agreement as to the shape of the r-height curve. 



It would now be instructive to compare the bendings obtained from 

 the various models with values obtained from each of the 5-year mean 

 A^ profiles from different climatic regions. The 5-year mean A'^ profiles 

 were obtained for both summer and winter for a variety of climates as 

 represented by the states of Florida, Texas, Maine, Illinois, Nevada, 

 California, North Dakota, Washington, Nebraska, Wyoming, and by the 

 District of Columbia. 



Comparisons of the bending obtained from the 4/3 earth model and 

 the bendings obtained from the 5-year mean A^ profiles with the reference 

 atmospheres are shown in figures 3.10 and 3.11. These figures were 

 selected to illustrate the range of agreement between the models and the 

 expected long-term average bendings. Figure 3.10 gives a comparison 



