uated considerably. The maximum ranges at which targets can 

 be detected is reduced somewhat. So it can be seen that when the 

 radar is most needed, atmospheric conditions are not the best for 

 target detection. However, so long as the sea is not too heavy, all 

 targets except the smallest growlers should be detected by radar 

 in time to avoid collision. Nevertheless, no vessel should ever feel 

 wholly secure in an advection fog when operating in ice areas. 

 At the present time radar is the greatest single aid in increasing 

 the safety of the vessel, but it cannot guarantee 100 percent safety. 

 The 3-cm. band radar has its maximum ranges decreased slightly 

 more in foggy weather than does the 10-cm. radar. This is due to 

 the fact that the shorter wavelengths are attenuated to a greater 

 extent by the moisture in the fog. 



In comparing the abilities of the 3-cm. and 10-cm. band radars 

 to detect icebergs it was found that each had its advantages. The 

 3-cm. radar used for this investigation had about 20 percent greater 

 maximum range which meant that targets were always detected 

 with the radar of that frequency first. However, because of the 

 narrow antenna pattern of the 3-cm. band radar the target was not 

 seen on every sweep. At near maximum range echoes were re- 

 ceived once in every three sweeps. This figure represents an 

 average and depends upon many factors such as roll and pitch of 

 the ship, heaving, and size of the target. Once a target had been 

 picked up by the 10-cm. radar it was missed for very few sweeps of 

 the antenna and presented a large echo on the PPI scope. The size 

 of the echo was due to the broad antenna beam pattern. It was 

 noted that without exception once the 10-cm. band radar had de- 

 tected a target the echo was much easier to follow on that radar. 

 Thus we have again the balance of abilities, greater maximum 

 range against more reliable presentation. 



The one great advantage the 3-cm. radar has over the 10-cm. 

 radar is that of definition. The place where this comes to the front 

 in ice detection is in field ice. The definition properties of the 3 cm. 

 are far superior to those of the 10-cm. band for this work. The 

 outline of the field ice is reproduced with excellent fidelity by the 

 3-cm. radar. Leads and open water can easily be identified. Of 

 course, the weather must be fairly moderate or the field ice will not 

 be detected at all by either radar. This same advantage of the 

 3-cm. radar holds good in channel work or in a harbor. Often it 

 was possible to proceed through ice fields at night by radar Conning 

 using the 3-cm. radar. On the PPI scope the open leads were evi- 

 dent from a minimum range of 400 yards out to 10,000 yards which 

 was very close to the maximum range that field ice was detected. 



A few experimental runs were made using as targets the fishing 

 schooners which frequent the area of the Grand Banks. These 

 vessels were found to give about the same strength of echo as a 



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