208 



ANGLE-OF-ARRI\ AL EXPERIMENTS 



The excess modiiieJ refractive iudex M is given by 



nr 

 M ■ 10-" = -7 - 1 



-©'- 



- 1~(1 - wi)- 



h 



(9) 



If now the relation for the distance s is solved simul- 

 taneously with the equation stating Snell's law of 

 refraction, we have the angle of arrival « as a function 

 of the excess modified refractive index M, uniquely 

 relating the angular deviation from true bearing to 

 the distribution of modified refractive index required 

 to produce that deviation. 



13.2.3 Analysis of the BTL New York- 

 to-Beer's Hill Circuit 



The results obtained by Bell Telephone Laboratories, 

 Inc., on measurements of the angle of arrival of micro- 

 waves in the X band are contained in two BTL re- 

 ports.^'- The New York-to-Beer's Hill propagation 

 circuit proved to be the more suitable for the meteor- 



ological analysis of angle of arrival. On this path the 

 transmitter was located on the New York Telephone 

 building at an elevation of 493 ft above mean sea level; 

 the receiver was erected on top of Beer's Hill at an 

 elevation of 353 ft. The propagation path had a length 

 of 24.08 miles and ran several degrees east of north 

 from Beer's Hill to New York. The bearing from re- 

 ceiver to transmitter on this circuit on the basis of 

 true earth geometry is 0.11 degree below zero eleva- 

 tion angle of Beer's Hill. 



During the summer of 1944 a limited number of 

 vertical temjDerature and humidity soimdings were 

 secured by personnel of Wave Propagation Studies, 

 Evans Signal Laboratory, at a 400-ft radar tower in 

 Oakhurst, New Jersey. The location of the tower is 

 shown on the map in Figure 5. The tower stands on a 

 hill 128 ft above mean sea level. The limit of observa- 

 tion is 375 ft above the base of the tower; hence the 

 absolute elevation was 503 ft. It follows that soundings 

 over the height of the tower sample the atmosphere 

 between approximately 11 ft above the transmitter and 

 225 ft below the receiver. 



NEW YORK CITY 

 140 WEST ST 

 TRANSMITTER 492' 



PEgJH 



amboy' 



BEER'S HILL 

 RECEIVER 353 



FREEHOLD 



DEAL 

 , TRANSMITTER 2IO' 



400" TOWER TR -28*^) 

 BASE 128' ABOVE ( 

 SEA LEVEL \ 



13.2.4 'Yhe Angle of Arrival Deduced from 

 Type Cases of Atmospheric Stratification 



When the path is confined to a layer between receiver 

 and transmitter, there are two limiting paths, as illus- 

 trated in Figure (iA : I'atli A leaving the transmitter 

 at some angle ji -C Q and arriving at the receiver with 

 a = 0; Path B leaving the transmitter at an angle 

 j3 = and arriving at the receiver with a > 0. By 

 applying the equations deduced from theory and ex- 

 pressed by data in Table 1, the necessary and suflficient 



Table 1 



Deviation 



a at /3 at of a and IS 



receiver transmitter from true 

 Patli (degrees) (degrees) bearing m 



Figure 5. Plan view of propagation patlis. 



modified refractive index distributions with height in 

 the layer can be evaluated for the limiting paths A 

 and B and for all intervening paths. Table 2 shows the 

 value of the stratification parameter m required. We 

 therefore conclude that, for a path confined to the 

 layer between transmitter and receiver, the deviation 

 from true bearing must be confined to the interval 

 +0.111 to +0.236°, and the change in the modified 



