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{d) Operator's ability. The best equipment known today can give 

 maximum performance only in the hands of well-trained and experi- 

 enced operators. The performance and interpretation of radar may 

 differ as much as 33 percent according to whether the operator is 

 skilled or unskilled. 



Ice does not have the microwave reflection properties of metals and 

 is therefore a poorer reflector of radar waves than are ship-type tar- 

 gets. Even ships of moderate size give greater target range than 

 the largest bergs encountered. 



Over-water return from ice targets follows the same type echo- 

 strength-to-range relationships as have been found for ship targets. 



During rough weather, representations on PPI and A-scopes may 

 become momentarily blurred but should clear in 1 or 2 sweeps of the 

 antenna. 



It is quite possible that a target may be lost due to the ducting effect 

 of the beam caused by air conditions. This happens occasionally but 

 not to the extreme that the target is completely lost. 



The blending of the sea return and the echo from growlers offers 

 the greatest problem of detection, but an alert operator can reduce 

 the hazard. In moderate seas the growlers alternately appear and 

 disappear from the scope in approximately the same position each 

 time, whereas the sea return will fail to appear in the same relative 

 position ; likewise, the sea returns are not as strong as those reflected 

 from the ice. 



Caution is essential during periods when ships are navigating in 

 consolidated pack during low visibility. Large bergs can be distin- 

 guished from adjacent pack ice returns at ranges of 4,000 yards or 

 more, but these are obscured by pack ice echoes at lesser ranges and 

 what actually are shadows of large bergs can be very easily mistaken 

 for open water. Antijam controls are of some value in differentiating 

 between pack ice and large bergs at reduced ranges but should not be 

 relied upon. 



Floes up to 6 miles from the ship are well patterned on the PPI ; 

 radar may therefore be of considerable assistance in picking leads 

 through the ice. It should be remembered, however, that ice less than 

 1 foot out of water cannot be detected by radar. 



In no case should the radar be accepted as 100 percent accurate, re- 

 sulting in the relaxation of safety precautions dictated by the rules 

 of good seamanship. It is a valuable and essential aid in ice naviga- 

 tion which, when judiciously used, safeguards the ship from many of 

 the hazards presented by ice. 



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