94, TECHNICAL SURVEY 
3 _iN DEGREES 15 10 
Z IN DEGREES ——=— 
te 20 
5| 
16 
aie 3 
i 
= 
8 ~ 
2 re 
2 3 wm 
i 2 S) 
i 2 
5 1 EB 
ol a 4 
<= 2 2 tn 
1 
RANGE IN MILES 10 30 50 
70 90 
RANGE IN MILES 
Fiaure 38. Line-of-sight curves. Ficure 39. Line-of-sight curves. 
shields at several distances. This graph is intended 
for 200 me but may be used on other frequencies by 
changing d; in proportion to the change in X. It 
enables one to make an estimate of the effectiveness 
of a shield. Thus if a shield is 1 mile away it may be 
neglected for values of 6, in excess of +3°. Likewise 
objects below —3° in the shadow region would give 
weak echoes in most cases. For intermediate angles 
the relative intensity may be read from the curve. 
For shields closer than 0.1 mile the methods dis- 
cussed on pages 84-86 should be employed. 
Figure 15 shows that the relative intensity of a 
= 
2 
50.8 
z 
a 
4 
= 
w 
2 on 
2 INTENSITY RELATIVE TO THE 
a INTENSITY WITHOUT THE RIDGE 
VHF- 200 MC 
° 
@4 IN DEGREES 
Ficure 40. Diffraction over a ridge. (200 me) (For other frequencies change d, in proportion to the change in wavelength.) 
