This report presents the results of 

 an evaluation of the AN/APS-131 

 SLAR to detect icebergs. This 

 evaluation was conducted by IIP 

 from 7 to 1 6 June 1 988 in the 

 North Atlantic Ocean off New- 

 foundland, Canada. The funda- 

 mental goal of this research was 

 to provide guidance on the ability 

 of the AIREYE-equipped HU-25B 

 to perform the iceberg detection 

 mission of the International Ice 

 Patrol. Specifically, there were 

 two objectives: 



1 . Determine the best 

 altitude for iceberg searches, and 

 predict the probability of iceberg 

 detection as a function of sea 

 state, lateral range, and iceberg 

 size. 



2. Compare the iceberg 

 detection capability of the APS- 

 131 SLAR with the APS-1 35 

 SLAR. 



This report will also compare the 

 results of this evaluation with the 

 results of two previous SLAR 

 iceberg detection evaluations. 



Background 



Previous SLAR Studies 



Two previous SLAR studies have 

 been conducted to evaluate the 

 ability of the AN/APS-135 SLAR to 

 detect icebergs. During April 

 1984, BERGSEARCH '84 was 

 conducted to evaluate the ability of 

 three SLARs and two Synthetic 



Aperture Radars (SAR) to detect 

 small icebergs and growlers. The 

 M/V POLARIS provided surface 

 truth data. Results of the data 

 analysis reported in Rossiter et al 

 (1985) show greater detectability 

 is obtained with lower sea states, 

 at lower altitudes within the 

 operating envelope of each 

 system, and when viewing targets 

 across rather than up or down 

 wind and sea. BERGSEARCH "84 

 data also demonstrated that ships 

 and iceberg targets generally do 

 not have different SLAR signa- 

 tures. 



The 1985 SLAR Detection Experi- 

 ment was designed to determine 

 SLAR's ability to detect various 

 search and rescue and iceberg 

 targets at all ranges out to 27 nm 

 (50 km). The iceberg detection 

 results reported in Robe et al 

 (1985) indicate medium icebergs 

 are detectable nearly 100% of the 

 time in up to 2 m seas, small 

 icebergs are easier to detect at 

 lower altitudes and with a smaller 

 swath width, and growlers are 

 detectable more than 90% of the 

 time in seas less than 1 m. Also, 



Table E-1. Aircraft Operatirig Characteristics. 



both growlers and small icebergs 

 in seas less than 1 m appear to be 

 just as detectable at lateral ranges 

 between 25 and 50 km as they are 

 at ranges less than 25 km. Fi- 

 nally, they noted similar iceberg 

 detection performance of the AN/ 

 APS-135 SLAR in this experiment 

 and in BERGSEARCH '84. 



Description of Aircraft 



A Coast Guard HC-130H and HU- 

 25B were the two U.S. aircraft 

 used in the experiment. The HC- 

 130H is a long-range four engine 

 turboprop reconnaissance aircraft, 

 whereas the HU-25B is a medium- 

 range twin engine fan jet aircraft. 

 CG-1503 from Coast Guard Air 

 Station Elizabeth City, North 

 Carolina, was the HC-130H 

 aircraft in the experiment, and CG- 

 21 03 from Coast Guard Air Station 

 Cape Cod, Massachusetts, was 

 the HU-25B. Table E-1 lists the 

 operating characteristics of the 

 two aircraft. 



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