264 RADIO WAVE PROPAGATION EXPERIMENTS 
Taste 4. Reflection coefficient of level, grass-covered ground. > =9cm. Grazing angle 10°. 
Vertical polarization Assumed constants Horizontal polarization 
Ground conditions Calculated Observed €r o mhos/m Calculated Observed 
Grass cut very short and rolled dry. 0.47 0.46 3 0.055 0.79 0.79 
(No rain for at least 7 days.) 
Cut very short and rolled wet. 0.36 0.37 6 0.11 0.86 0.86 
(Several hours of rain on previous night.) 
Grass about 1 in. high, wet. 0.36 0.51 6 0.11 0.86 0.83 
(Same day as previous test.) 
TasLe 5. Magnitudes p,.and p,, observed values. > = 9:cm.1,2 
Heigl of Grazing angle 
vegetation, 22° 36.5° 56.5° 
Appearance of ground v h v h v h 
Bare 0.32 0.86 0.50 0.78 0.58 0.74 
True leaves beginning to form, ground visible 3-4 0.40 0.50 0.44 0.55 0.47 0.56 
Dense clumps, ground showing in places 9-12 0.18 0.65 0.23 0.58 0.33 0.49 
Ground almost obscured 20-25 0.06 0.32 0.10 0.39 0.17 0.41 
Ground completely obscured 35-45 0.04 0.19 0.05 0.26 0.11 0.28 
refer to various types of grass-covered earth. 
The results obtained with the portable 10-cm set 
appear on Figures 11, 12, 13, and 14. These graphs 
show clearly the influence of vegetation on the re- 
flection coefficient. Consult Table 5 tor corresponding 
Tesults at 9 cm. 
0.8 
° 
a 
O VERTICAL POLARIZATION 
X HORIZONTAL POLARIZATION 
PLACE-HICKSVILLE AIRPORT 
EARTH- ROLLING FIELD, SOIL DRY, 
GRASS 4" LONG 
REFLECTION COEFFICIENT Pp 
°o fo) 
to > 
0 4 8 12 16 
GRAZING ANGLE IN DEGREES ¥ 
Ficure 11. Reflection coefficient p versus y. A=10 cm. 
d=225 ft. Grass covered ground. 
© VERTICAL POLARIZATION 
* HORIZONTAL POLARIZATION 
PLACE-SPERRY “BACKYARD” 
EARTH-SLIGHTLY ROLLING, GRASS 
4-18" HIGH, DRY 
REFLECTION COEFFICIENT P 
GRAZING ANGLE IN DEGREES ¥ 
Ficure 12. Reflection coefficient p versus Y. A=10 cm. 
d=100, 225 ft. Grass covered ground. 
Since, however, 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 
teflection 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- 
© VERTICAL POLARIZATION 
® HORIZONTAL POLARIZATION 
PLACE-NY STATE AG INST 
EARTH-BEET FIELO WITH WEEDS 
REFLECTION COEFFICIENT P 
° 4 8 12 16 20 24 268 
GRAZING ANGLE IN DEGREES ¥ 
Figur 13. Reflection coefficient p versus Y. A= 10 cm. 
d=100 ft. Beet field with weeds. 
0.8 
© VERTICAL POLARIZATION 
xX HORIZONTAL POLARIZATION 
PLACE-NY STATE AG INST 
EARTH- PINE TREES 3'-10° TALL, 
BUSHES, WEEDS IN GRAVELLY 
SOIL 
REFLECTION COEFFICIENT 
So 
> 
GRAZING ANGLE IN DEGREES 
Ficure 14. Reflection coefficient p versus y. A=10 cm. 
d=102, 200 ft. Trees, bushes, weeds in gravelly soil. 
