Iceberg Effective Echoing Area 



In the free space radar equation: 



P r _ G 2 XV 



? ( "(4x) 3 /i! 4 



(2) 



The term a is denned as the effective echoing area or the radar cross sec- 

 tion and has the dimensions of length squared. This parameter may be 

 thought of as the area of a perfectly conducting sphere which is equiva- 

 lent to the echoing strength of the target; or, as the effective scattering 

 cross section which a target would have if it scattered as much energy in 

 all directions as it actually does scatter in the direction of the radar re- 

 ceiver. The dependence of the radar cross section on the shape of a target 

 is best illustrated by considering that the radar cross section of a large 

 metallic plate placed perpendicular to incident radiation is 1,200 times 

 that of a sphere of equivalent area. The radar cross section of a battleship 

 is approximately 3.2 X 10 7 sq. feet and that for a 10,000 g.r.t. merchant ship 

 approximately 1.2X10 4 sq. feet. The value of <r, for a given shaped target 

 may not vary in direct proportion with its projected area; in fact, the direct 

 variation is true only for a few simple geometric forms (i.e. sphere, curved 

 surface). 



Seemingly the task of analyzing the aspect of the iceberg targets is an 

 insurmountable one in view of the fact that the micro and macro mor- 

 phology of icebergs varies considerably from berg to berg and unques- 

 tionably no two bergs are alike. The theoretical computation of the ef- 

 fective echoing area based on the geometrical shapes involved is neither 

 meaningful nor feasible for icebergs. However, as the effective echoing 

 area does provide an excellent means of evaluating ice as a radar re- 

 flector it was desirable to determine the magnitude of this parameter. 

 Not until the empirical relation between the maximum range of detection 

 and the physical cross-sectional area was derived was it possible to 

 attempt this. 



Iceberg Ice Reflection Coefficient 



Because the correlation ratio for the empirical relation (1): 



# 4 = 3.8X10 13 A (1) 



is 0.81, we may assume that the theoretical fourth power relation between 

 range and actual cross-sectional area is true for icebergs. However, as 

 mentioned earlier, only a few geometrical shapes show a direct variation 

 of the effective echo area with the actual area. The sphere segment has a 

 radar cross section given by 



<r = irr~ (4) 



where a is the radar cross section and r is the radius of the perfect con- 

 ductor. The segment may be viewed either on the concave or convex side. 



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