posed that these be tried in the ice areas with the ultimate goal of 

 safe navigation for all ships, naval and commercial, through the 

 area of the Grand Banks during the ice season. This study should 

 be broadened to include different types of radar and especially the 

 commercial models which are appearing in ever increasing num- 

 bers on the merchant ships. 



Results of Work During 1945 and 1946 



During the 1945 and 1946 ice seasons the two radars mentioned 

 previously were tested arid compared for their respective merits 

 and faults in the problem of the radar detection of floating ice. Ice 

 proved to be a poor reflector of radar waves. A large iceberg (i.e. 

 200 feet high, 400 feet long) returned an echo no stronger than a 

 small ship (C. G. C. Tampa, 90-foot mast, 240-feet long) . Although 

 each of these targets would easily be detected by either radar in 

 plenty of time to avoid collision, the majority of ice fragments are 

 a great deal smaller than a large berg. These small bergs and 

 growlers are capable of causing serious damage to a vessel. It was 

 found that small bergs and growlers often were undetected in mod- 

 erate sea conditions. As the state of the sea and wind increased in 

 intensity so did the size of the berg which might go undetected. 

 On one particular occasion a 50-foot berg was not detected by either 

 radar. It was seen visually at a range of less than 1,000 yards. In 

 periods of poor visibility or darkness this fact would present a 

 serious problem for ships steaming through the ice area. It must 

 be remembered that on the experimental vessel the radars were in 

 excellent operating condition and that a continuous watch was 

 being stood on both sets. 



The strength of the sea return on the scope is the primary limit- 

 ing factor in determining the size of berg which might go un- 

 detected. The greater this sea clutter the larger becomes the 

 minimum size of berg which can be detected. It was noted that the 

 size of the wave does not necessarily affect the amount of scope 

 clutter. Rather, it appears to be the amount of chop or foam which 

 is the predominant factor in producing sea return echoes on the 

 radar scope. This seems logical because the amount of chop usually 

 depends on the vertical build-up of the wave to the point where the 

 tops are blown off. This vertical surface presented to the radar is 

 what causes excessively strong radar sea clutter as more energy 

 is reflected back from each outgoing pulse. A great deal of vertical 

 surface is present, especially up-wind, in conditions of heavy chop. 

 Without fail a heavier sea return clutter was noted in the direction 

 of the wind. Sometimes it was possible to estimate the direction 

 of the wind with a fair degree of accuracy from the picture on the 

 PPI scope. A small chop appeared to give a larger sea return 



183 



