EARTH CONSTANTS IN THE MICROWAVE RANGE 



141 



12 16 20 



GRAZING ANGLE IN DEGREES ^i 



Figure 6. Reflection coefficient p' versus 'p. X= 10 cm. 

 d = 90ft. 



12 16 20 



GRAZING ANGLE IN DEGREES ^ 



Figure 7. Reflection eoeflicient p' versus ip. X=10 cm. 

 d = 300, 90 ft. 



Figures 6 and 7. The theoretical curves in Figure 6 

 correspond to a perfect dielectric (o- = 0) with cr = 

 10. Since the conductivity of the soil is not zero, the 

 true value of the reflection coefficient for vertical 

 polarization cannot be zero at the Brewster angle. 

 The data seem to confirm this point. 



The data of Figure 7 refer to moist and very smooth 

 beach sand. It is thought that these observations are 

 the most reliable so far as self -consistency is con- 

 cerned. Again the computed curves refer to a perfect 

 dielectric with er = 15. 



An important difference between the measurements 

 at 9 cm at a fixed location and those made at 10 cm 

 with the portable setup consists of the fact that at 9 

 cm direct absorption measurements could be per- 

 formed in addition to measurements of the reflection 

 coeffieent. The electrical constants could thus be deter- 

 mined at 9 cm without amlaiguity. 



Fresh Water and .4% Salt Solution {or Sea Water). 

 (1) Tap water. Table 3 gives the results on the reflec- 

 tion coefficients of tap water (temperature not given). 



The values of €r and a which best represent both the 

 reflection and absorption data are tr — SO, o- = 2.2 

 mhos per m, and ej = 11.9. 



2. Fresh ii-ater pond. The results on 10-cni waves 

 are collected in Figure 8.' These data refer to a fresh 

 water pond and the theoretical curve corresponds to 

 a smooth and perfect dielectric surface with £r = 80. 

 The curves do not fit too well at the smaller grazing 

 angles. If the conductivity were taken into account, 



8 12 16 20 



GRAZING ANGLE IN DEGREES tji 



Figure 8. Reflection coefficient p' versus \p. X= 10 cm. 

 d = 90, 225 ft. Fresh water pond. 



presumably a better fit might be achieved. Two points, 

 marked Ford,^'^ taken from Table 3 were included 

 for comparison. 



3. Salt solution. In order to simulate sea water a 

 4 per cent salt solution was ^ised for the determination 

 of the reflection coefficient. At 9 cm the best fit was 

 obtained with e^ — 80, o- = G.l mhos per m, and e; 

 — 00. 



4. Sea water. Figure 9 gives the results obtained 

 at 10 cm. The computed curves drawn to fit the data 

 correspond to e^ =69, o- = 6.5 mhos per m, e; = 39. 

 It appears that the data can be fitted with the com- 



