4-5] 



REFLECTION OF PLANE WAVES FROM THE GROUND 

 120 



100 



80 



e' 60 



40 



20 







183 



10 



10^ 



103 



104 



105 



FREQUENCY (Mc) 

 Fig. 4-5 Dielectric Properties of Pure, Fresh, and Sea Water. 



10' 



Sea Water 



Tresh Water 6?S\t\ <^" 



10 102 103 



FREQUENCY (Mc) 



Fig. 4-6 Dielectric Properties of Pure, Fresh, and Sea Water. 



frequency, taken from Saxton.^ The curves for temperatures of 0° and 20°C 

 bring out a dependence on temperature as well. 



Figs. 4-7 through 4-10 show the magnitude and phase angle of the 

 reflection coefficient of sea water for a temperature of 10°C at several 

 wavelengths. Similarly, Figs. 4-11 and 4-12 show the reflection coeffi- 

 cients for two different types of ground. For most airborne radar work, 

 solid ground may be treated as a pure dielectric. These figures bring out 

 clearly the diflFerence between horizontal and vertical polarization. For 

 horizontal polarization, there is only a slight variation in magnitude and 

 phase of the reflection coefficient with depression angle. For vertical 

 polarization, however, there is a marked variation, caused by a partial 

 impedance match of the two mediums which occurs at the Brewster angle. 

 The reflection coefficient reaches a minimum magnitude and has a phase 

 angle of 90° at this angle (the Brewster angle itself depends on frequency). 



6J. A. Saxton, "Electrical Properties of Sea Water," Wireless Engineer 2^, 269-275 (1952). 



