Appendix C 



Effects of Side Looking Airborne Radar (SLAR) 

 on Iceberg Detection During the 1983 and 1984 



International Ice Patrol Seasons 



Lieutenant (jg) Neal Thayer, USCGR 



Introduction 



Discussion 



The AN/APS-135 Side-Looking 

 Airborne Radar (SLAR) was 

 introduced to international Ice 

 Patrol (IIP) reconnaissance flights 

 at the beginning of the 1 983 IIP 

 season, the first continuous 

 operational use of SLAR by IIP. 

 The AN/APS-135 is a 

 replacement forthe AN/APS-94D 

 SLAR which was occasionally 

 used by IIP on an experimental 

 basis starting in 1 976. With this 

 more powerful AN/APS-1 35 

 SLAR, visual reconnaissance was 

 replaced by SLAR as the main 

 search method, and 

 reconnaissance coverage of the 

 IIP region was significantly 

 increased. Since the IIP region is 

 an area of frequent heavy fog and 

 bad weather, the all-weather 

 capability offered by SLAR 

 increased both the number of 

 days that IIP could conduct 

 reconnaissance flights and the 

 amount of reconnaissance 

 coverage of search areas under 

 conditions of intermittent visibility. 

 In addition, longerflights became 

 possible with SLAR, and regular 

 reconnaissance of the eastern 

 part of the region began. This 

 increased capability is evident in 

 that prior to the 1 983 season, it 

 was necessary to maintain an Ice 

 Reconnaissance Detachment 

 (ICERECDET) in Newfoundland 



continuously during the IIP 

 season, while in 1 983 and 1 984, 

 ICERECDET's were deployed 

 every other week with the same 

 number of flight hours as in 

 previous years. 



The introduction of SLAR 

 constitutes a major change in the 

 IIP iceberg detection techniques. 

 An important question arises from 

 this change. What effect does 

 SLAR have on the number of 

 icebergs south of 48°N, the 

 traditional indicator of the severity 

 of an iceberg season? This 

 question is addressed in Part b. 

 of the following section using the 

 IIP data base forthe years 1960 

 through 1984, data contained in 

 the IIP historical data file. Part a. is 

 a brief discussion of the effect on 

 the number of icebergs estimated 

 south of 48°N due to the 

 introduction of the iceberg drift 

 prediction model (IBERG) to 

 International Ice Patrol operations 

 in 1979. 



In 1900, the U.S. Naval 

 Hydrographic Office began 

 estimating the number of 

 icebergs passing south of 48°N 

 as a measure of the severity of 

 each iceberg year. The 

 International Ice Patrol, with its 

 beginning in 1914, continued to 

 keep records of this number. 

 Prior to 1983, the mean annual 

 number of icebergs south of 

 48°N was 364, with a range from 

 in 1 966 to a record of 1 584 in 

 1972. The number of icebergs 

 south of 480N was 1348 in 1983, 

 representing the fourth highest 

 number on record, and 2202 in 

 1984, the new record. Given the 

 increased iceberg detection 

 capability offered by SLAR, it 

 seems possible that these 

 elevated figures for 1 983 and 

 1 984 are primarily the result of 

 SLAR reconnaissance. As a 

 result, comparing the 1 983 and 

 1 984 numbers of icebergs south 

 of 48°N directly with those of 

 previous years might provide a 

 misleading indication of the 

 severity of these two seasons. 



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