EARTH CONSTANTS IN THE MICROWAVE RANGE 



145 



ft. Tlie reeeiver was placeil on a ship at a cuustaiit 

 height of about 33 ft. Tlie field strength of the radia- 

 tion was measured as a function of the distance from 

 the transmitter. This distance varied between 3,500 

 and 4,3,000 yd. The observed values of tlie field 

 strengths correspond well with calculations based on 

 electromagnetic theory. 



In a second series of experiments" both the trans- 

 mitter and receiver were stationary. The topography 

 of the location and the experimental setup are rep- 

 resented schematically in Figure 15. The main con- 

 clusion drawn from these experiments was that even 

 for a calm sea (vertical amplitude of the waves less 

 than 8 in.) the mean amplitude of the reflected ver- 

 tically i^olarized beam was only about half the steady 

 amplitude of the direct wave. The amplitude of the 

 reflected wave, how'ever, occasionally rises to greater 

 values than that of the direct wave, but this lasts only 



t.O 



0.9 



0.8 



0.7 



0.6 



f. 



0.5 



0.4 



0.3 



0.2 



0.1 



v-. :»- 



— .-^ t 



• • \ 



• •• \ . 



■ ^ 



* • • Jl 



* \ ~ 



for short lengths ul' time of tlie order of 0..j sec. 



In the case of the reflection of horizontally polar- 

 ized radiation at the surface of a smooth sea it is 

 known that even for grazing angles as large as 10° 

 the amplitude of the reflected wave is very nearly equal 

 to that of the direct wave. The irregularities of the 

 sea, however, reduce the amplitude of the reflected 

 wave. This reduction is due to scattering, i.e., to non- 

 specular reflection of the radiation by the irregu- 

 larities of the sea surface. It is recalled here that the 

 surface irregularities will play an important role as 

 soon as they are larger than X/i//, A being the wave- 

 length and \\j the grazing angle in ]-adians. 



The Eadiation Laboratory workers,"'" used an air- 

 plane as the carrier of the reeeiver flying toward the 

 transmitter. For 10- and 3.2-cm waves the latest re- 

 svUts are given in Figures 16, 17, 18, and 19. These 

 show that theory and experiment check satisfactorily 

 for vertical polarization, but for horizontal polariza- 



1.0 



0.9 



0.8 



0.7 



0.6 



0.5 



0.4 



0.3 



0.2 



0.1 



12 3 4 OVER SEA 



ORAZINC ANGLE IN DEGREES 



Figure 18. Sea reflection coefficient p,. versus grazing 

 angle \^ at 8.2 cm. Vertical polarization. 



• • / 



12 3 4 OVERSEA 



GRAZING ANGLE IN DEGREES 



Figure 19. Sea reflection coefficient P;, versus grazing 

 angle ^ at 3.2 cm. Horizontal polarization. 



