50 



OCEAN ELECTRONIC NAVIGATIONAL AIDS 



Figure 4—7. — PPI picture showing portion of sea area (left-hand portion of picture) 

 obscured by a heavy rain squall which is local in nature (special 3 cm. Radar). 



(4) Certain types of objects, because of their characteristics or motion, 

 may go undetected. For example, the Coast Guard's study of 

 Radar detection of floating ice has revealed that while icebergs 

 can ordinarily be observed, pieces of ice large enough to damage 

 a ship may go undetected. Ice and some other things, therefore, 

 due to physical characteristics and reflecting properties, are rela- 

 tively poor targets. A low-lying point of land is another example 

 of a relatively poor target. The motion of small objects, such as 

 small buoys and boats, caused by bobbing up and down in a seaway 

 tends to reduce the echo returned to the Radar. These considera- 

 tions become particularly important when such things as sea 

 return and rain, are present to reduce the Radar visibility. 

 While Radar has limitations, its advantages more than compensate for 



these limitations. The distinct operational advantages are summarized 



below : 



(1) It is the best anticollision device yet perfected. 



(2) It makes for greater safety while piloting or making landfalls during 

 ' periods of low visibility. 



