Classifying SLAR-detected icebergs accord- 

 ing to size cannot be done with much confi- 

 dence. 



Ice Patrol's reconnaissance strategy 

 was designed to take maximum advantage of 

 the SLAR'sall-weathercapability, while at the 

 same time, recognizing its detection and tar- 

 get discrimination uncertainties. Ice Patrol 

 searches for icebergs using USCG HC-1 30H 

 long range surveillance aircraft operating out 

 ofSt. John's, Newfoundland, Canada forseven 

 days every other week. It takes approximately 

 four flight days to investigate a 1 20 nm swath 

 along the entire limits of all known ice. Daily 

 patrols are conducted using a parallel search 

 pattern with track spacing of 25 nm and the 

 SLAB range scale set at 27 nm. Thus, the 

 SLAR gets two looks at most of the search 

 area. The 200% coverage seeks to ensure 

 that no growlers or small icebergs are missed 

 andtogettargetmovementinformation (course 

 and speed for ships), which can be deter- 

 mined by the target's displacement between 

 successive search legs. 



The addition of the SLARtremendously 

 improved Ice Patrol's reconnasaince efficiency. 

 After the addition of the SLAR, Ice Patrol was 

 able to get the same amount of patrols in a 

 week as two weeks without the SLAR. SLAR 

 target identification remained problematic. 

 Targets on the outside of the airplane's track 

 are an identification problem as the radar 

 sweeps this area once and the SLAR operator 

 is unable to deduce any drift information. This 

 outside area is typically one third of the total 

 search area. 



FLAR 



When the Coast Guard began evaluat- 

 ing the AN/APS-1 37 Fonward-Looking Airborne 

 Radar (FLAR) as a search and rescue target 

 detector. Ice Patrol recognized its potential to 



detect and identify icebergs. The FLAR, which 

 was developed by Texas Instruments to de- 

 tect small targets in high sea states, is an X- 

 band air-to-surface radar capable of Inverse 

 Synthetic Aperture Radar (ISAR) mode and 

 seemed ideally suited for the Ice Patrol envi- 

 ronment. It is a high power radar that com- 

 bines long-range detection and target imaging 

 capabilities into a single, integrated system. 



The AN/APS-137 has four operating 

 modes, three of which are variations of a 

 surface search mode (search, navigate, and 

 periscope), and an imaging mode. In the 

 surface search modes, the radar uses a real 

 aperture, while the imaging mode is ISAR. 



The following is a brief summary of the 

 individual modes: 



1. Search mode: designed for 

 wide-area searches. 



2. Periscope mode: designed for 

 shorter range, low altitude (<3000ft) searches 

 for small targets. The high antenna scan rate, 

 the radar pulse frequency and duration, and 

 sophisticated data processing permit reduc- 

 tion in sea clutter and an amplification of small 

 target return. 



3. Navigate mode: wide-area 

 search, but low antenna scan rate, which is 

 suitable for navigation and can be used for 

 target detection. 



4. Imaging mode: The ISAR is a 

 synthetic aperture radar (SAR) that takes ad- 

 vantage of the rotation of the target, rather 

 than the movement of the aircraft. In the 

 imaging mode, the radar's antenna stops ro- 

 tating and directs its radar beam at the target. 

 While imaging,the radar processes only range 

 data, generating a range versus Doppler dis- 

 play. The information is then converted into a 



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