140 



REFLECTION COEFFICIENTS 





O 



o 



2 

 O 



I- 



o 



UJ 



_J 

 h. 

 \U 

 d: 



12 IS 20 24 



GRAZING ANGLE IN DEGREES ^ 



Figure 4. Reflection coefficient p' versus i/-. X= 10 cm. d = '325, 100, 75 ft. 



graph do not ncee.ssarily represent the best fit. These 

 curves were computed for €r = i and o- = (perfect 

 dielectric). The experimental Brewster angle turns 

 out to be around 23° (grazing angle). 



The experimental results for clay-sand soil are 

 ffiven in Figure 5. The theoretical curves are the 



GRAZING ANGLE IN DEGREES ^r 



Figure 5. Reflection coefficient p' versus i/-. X= 10 cm. 

 d=100, 300 ft. 



same as tho.se given in the preceding case, that is, 

 for £r — 4 and o- = 0. It will be noted that the fit 

 with the experimental values is less satisfactory in 

 this case. The author attributes the discrepancy be- 

 tween the observed and computed \'alues of the re- 

 flection coefficient, in part, to the quality of the soil 

 which consisted of lumps of about a half wavelength 

 diameter. In general the roughness of the ground con- 

 tri I lilies considerably to scattering. It is rather to be 

 expected that a theoretical curve representing specular 

 reflection coefficients from a smooth surface should 

 not fit well the experimental data referring to such 

 a rough ground. 



SalitraU'/J Ground. Table 2 represents the results 

 obtained at U cm for the reflection coefficient of sat- 

 urated ground. 



The most suitable values of £,■ and cr or t; to fit both 

 reflection and absorption measurements are tr = 24, 

 (J = 0.66 mhos per meter, and t; = 3.56. 



Tests carried out at 10 cm on ground of somewhat 

 similar type (tidal flat and moist sand) are given in 



Table 2. Reflection coefficients of saturated ground. X = 9 cm.'^^ 



