between iceberg radar cross section and actual cross section, this power 

 ratio becomes 62.5 for equivalent area targets. By consideration of equa- 

 tion (2) it is evident that this ratio represents the ratio of effect ive echo- 

 ing areas for equivalent-sized ship and iceberg targets. In other words 

 this ship reflected 62 times better than an equivalent size iceberg. Al- 

 though this value seems high a similar approach to the comparison of 

 effective echoing areas by more reliable observations gives similar results. 

 Examination of figure 25 reveals that the reflected power curves for both 

 the stern of the CGC Evergreen (740 sq feet) and the large iceberg (43, 900 

 s(|. feet) are practically identical. The ratio of areas is 59. 



Reflectivity Summary 



From the above considerations we can arrive at the conclusions that 

 iceberg ice has a low reflection coefficient very approximately 0.33 and 

 that this coefficient might increase with the addition of melt water; and 

 that Grand Banks icebergs appear to reflect 60 times (16 decibels) less 

 than a ship of equivalent area. 



ASPECT 



The traction of the power incident upon a target which will be returned 

 to the radar antenna is dependent on a parameter involving the dimen- 

 sions and orientation of the target, and usually the wavelength of radia- 

 tion. In this discussion we shall speak of both the radar cross section 

 (equivalent echoing area) and the target gain. Target gain may be 

 thought of as the degree to which a target directs the radar beam back to 

 the receiver and is proportional to the radar cross section, i.e.: 



G r = 



The dependence of these parameters, and therefore the reflected power, 

 on target orientation or aspect is very great, and the reflected power from 

 less complex targets than icebergs has been reported to change as much 

 as 20 decibels with a change of orientation of only few degrees. The 

 computation of radar cross sections for targets of complicated geometric 

 design is one that has repeatedly defied attempts of thorough analysis, 

 although recently the use of computers has allowed the problem to be- 

 come feasible. As no two icebergs or iceberg orientations are similar it 

 would be fruitless to compute the theoretical radar cross section for one 

 or many icebergs. Fortunately, as shown earlier the complex nature of 

 the iceberg aspect problem was simplified by the discovery of the direct 

 relation between the radar cross section and the actual cross section. 

 The quantitative generalization of this problem has many exceptions. 

 An iceberg with a smooth and vertical face (c.f. fig. 31) normally conforms 



71 



