EARTH CONSTANTS IN THE MICROWAVE RANGE 



143 



Table 4. Reflection coefficient of level, grass-covered ground. X = 9 cm. Grazing angle 10°. 



Ground conditions 



Vertical polarization 

 Calculated Observed 



Assumed constants 

 «r (T mhos/m 



Horizontal polarization 

 Calculated Observed 



Grass cut very short and rolled dry. 



(No rain for at least 7 days.) 

 Cut very short and rolled wet. 



(Several hours of rain on previous night.) 

 Grass about 1 in. high, wet. 



(Same day as previous test.) 



Table 5. Magnitudes p, and p^, observed values. X = 9 cm.^i^ 



Appearance of ground 



Height of 



vegetation, 



cm 



22° 

 V h 



Grazing angle 



36.5° 



V h 



56.5° 



V h 



Bare 



True leaves beginning to form, ground visible 



Dense clumps, ground showing in places 



Ground almost obscured 



Ground completely obscured 



8 12 le 20 



GRAZING ANGLE IN DEGREES ^l 



Figure 14. Reflection coefficient p versus ^. X=10 cm. 

 d=102, 200 ft. Trees, bushes, weeds in gravelly soil. 



Since, liowever, the data of Table 5 refer to wet 

 vegetation-covered ground, they cannot be compared 

 directly with the results at 10 cm since these seem to 

 correspond to dry vegetation. 



Table 6 gives the data obtained at 9 cm for un- 

 mown meadow land having an average variation in 

 ground level of about 7 cm. The ground was covered 

 with a dense layer of grass about 30 cm high. The 

 reflection coefficient of this surface was measured, 



then remeasured with the grass mown as short as the 

 roughness of the ground permitted. The turf was next 

 removed, some of the irregularities of the ground were 

 eliminated, and the reflection coefficient of the sur- 

 face so prepared was measured again. The results of 

 these measurements are to be found in Table 6. The 

 estimated reflection coefficient of level ground of the 

 same moisture content is also included here. 



Finally, the results on the electrical constants of 

 different kinds of grounds for 9-cm waves have been 

 collected in Table 7. 



Table 7. Electrical constants of the ground. X = 9 cm.ii^ 



