56 



FACTORS INFLUENCING TRANSMISSION 



.5° 



♦ — — 



1-5" ? >5" 3" -i.5' <!• 4 5" 



Figure 14. Amplitude p of the reflection coefficient 

 versus reflection angle '^ from 'I' = to * = 5.5° for 

 sea water. 



noiinced. Therefore in selecting a radar site, it is 

 preferalile to choose a location which is surrounded 

 l:iy relatively smooth ground. The electrical proper- 

 ties of the earth vary considerably for different 

 localities, so that it is necef^sarj' to studj^ the ground 

 conditions for each particular case. Experimental 

 data concerning reflection of very short waves from 

 ice- or snow-covered ground seem to be lacking. 

 Precise information might be of operational interest, 

 particularly in Arctic regions. Laboratory exper- 

 iments indicate that ground covered l\y ice or snow 

 will influence the propagation of short waves some- 

 what in the same wav as very dry ground. 



4.2.7 



Conductivity of Soil 



Extensi^'e in\'estigations have been made on the 

 conductivity of different tj^pes of soil, particularly 

 on low and medium frequencies. For 10 mc, the 

 observed values range from 6 • 10"^ mhos per meter 

 for chalk to 0.13 mhos per meter for blue clay. The 

 conduct ivitv increases with increasing moisture 



5° 



f 



1.5° 2° 2.5° 



Figure 15. Phase (f) of the reflection coefficient versus 

 reflection angle *■ from ^t = to vf = 5.5° for sea water. 

 Er lags Ej by (f). (From Radiation Laboratory Report 

 C-11.) 



4.2.6 



Overland Transmission 



Conditions over land are very different from those 

 found over the sea. Land as a reflecting surface has 

 larger irregularities and their effect is more pro- 



FiGURE 16. Amplitude of the reflection coefficient for 

 moist and dry soil. 



content, so that marked seasonal changes may be 

 anticipated for a given locality. It also varies with 

 frequency. Under field conditions it will not be 

 possible to measure the conductivity in individual 

 cases and one will ha\'e to assume a value of about 



