and the area. The AN/APS-15A radar has the PPI presentation 

 with a full 360° scan. It had all the latest refinements of aircraft 

 radar and proved to be a very good radar set. One of its biggest 

 advantages is the automatic sector scan which permits any desired 

 bearing to be searched rapidly and thoroughly. The size of the 

 sector can also be regulated to fit the needs of the search. The 

 excellent definition properties of the PPI scope is a very desirable 

 feature. Land masses are reproduced with maplike quality, their 

 outline being very nearly the actual outline of the terrain scanned 

 by the antenna beam. The one major drawback of this radar is 

 the very critical tilt control of the antenna. An operator must be 

 highly skilled in the use of the tilt control in order to get a thorough 

 search. The antenna axis is sensitive in tilt to less than 2° which 

 makes any search of an area extremely difficult. 



Operating Experience With Air-Borne Radar 



Ice bergs. — The maximum observed ranges on ice bergs varied 

 from 8 to 50 miles on both sets. The wide variation in maximum 

 range was due to the fact that all bergs were of different size and 

 the plane was being flown at a wide variety of altitudes. No 

 measurements of actual berg dimensions were made but it was esti- 

 mated that at 800 feet altitude a search by radar could be carried 

 out to 15 miles either side of the track line with bergs of 40 by 

 100-feet being detected. No difficulty was encountered with either 

 radar in tracking ice targets through the sea return. The problem 

 of sea return was eliminated by the correct use of the antenna tilt. 

 Targets were tracked in low visibility to a minimum range of less 

 than 1 mile through all states of sea on the PPI scope. Difficulty 

 was experienced in detecting icebergs in the field ice but outside of 

 the field bergs and growlers were readily recognized. Since the 

 speed of the plane relative to that of a ship is so great the identity 

 of the target cannot be determined by its movement nor can the 

 echo return from all types of ships be reliably distinguished from 

 the echo return of bergs. Steel vessels give a somewhat sharper 

 and brighter echo than do icebergs. The fishing vessels of the 

 Grand Banks however, present a target very nearly equal to a 

 berg in size and brightness. An experienced operator can tell a 

 steel vessel from a berg but it would be impossible to distinguish 

 between a berg and a fishing schooner. Furthermore, at short 

 ranges it was often possible to pick up numerous dories around 

 the fishing schooners just as growlers were often detected around 

 a berg at about the same ranges. 



Field ice. — The edges of field ice were picked up and followed 

 easily in heavy fog. The edge of the field up to 10 miles ahead was 

 readily distinguishable. It was possible to detect field ice in fairly 

 heavy sea clutter if the presence of the field ice was suspected, as 



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