It is kiiown only when a ship reports an iceberg which may be many 

 miles outside the ice limits and in an unexplainable position. Why 

 does this happen ? It happens mainly because of the present limita- 

 tions on ice observing by aircraft and vessel. Actually the area of 

 responsibility can only partially be searched. 



Even if the area of responsibility were much smaller, and more 

 aircraft were available for ice observing to enable complete coverage, 

 weather would rarely cooperate. Weather is a serious deterrent to 

 the accomplishment of the mission of the International Ice Patrol. 

 The most important portion of the area of responsibility is the vicinity 

 of the Tail of the Banks where the main trans- Atlantic shipping tracks 

 converge. Unfortunately, this area of complex oceanographic con- 

 ditions, where the cold waters of the Labrador Current meet the warm 

 waters of the Gulf Stream, is an area frequently plagued by dense fog. 

 Fog normally renders ice observation by aircraft ineffective for days 

 at a time during the crucial periods in April, May, and June, when 

 icebergs can normally be expected at the Tail of the Banks area. 

 The berg transport medium, the Labrador Current along the north- 

 east and east slope of the Grand Banks, is another area frequently 

 fogged in and characteristic of poor visibility. Under rare circum- 

 stances does the entire area of responsibility have good visibility. As 

 the flight tracks are normally 25 miles apart, a visibility of 121/2 miles is 

 required throughout to hope for complete coverage of the areas 

 planned. The track spacing is a compromise between the amount of 

 area that must be searched and the probability of detection of icebergs. 

 Two ice observers are required for each Ice Patrol flight to insure 

 maximum visual coverage. Even so, the observers must spend time 

 writing on the chart or in the log and cannot spend 100 percent of the 

 time observing. When the visibility is less than 121/^ miles radar is 

 depended upon to partially fill the gap. All targets are evaluated 

 and an attempt is made to visually identify those suspected of being 

 possible icebergs. Unfortunately radar cannot be relied upon to reg- 

 ister all dangerous ice in the area of coverage. Small bergs and 

 growlers are not normally detected by radar if the range exceeds 10 

 miles or if sea conditions are moderate to rough. Wlien sea con- 

 ditions are very rough the larger bergs will also be missed. Even 

 were radar able to detect all dangerous ice targets, the capability does 

 not yet exist to distinguish an iceberg target from a fishing vessel 

 target. There are plans in the near future to test a microwave radio- 

 meter, which if used conjunctively with radar may possibly solve the 

 target identification problem. The success of this instrument will 

 mean a large improvement in aerial ice observation but the inability 

 of radar to insure complete coverage remains a serioas handicap. 



Another serious obstacle to aerial ice observing is imperfect navi- 

 gation. In order to hope for complete flight coverage, the actual 



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