Discussion of 

 Iceberg and 

 Environmental 

 Conditions 



The number of icebergs that 

 pass south of 48°N in the 

 International Ice Patrol area each 

 year is the measure by which 

 Intemationai Ice Patrol has judged 

 the severity of each season since 

 1912 (Table 1). With 2202 

 icebergs south of 48°N, 1984 is 

 the record year with the previous 

 maximum in 1972 being 1587. 

 This record number and the near- 

 record for 1 983 ( 1 348, fourth 

 highest on record) are partially the 

 result of International Ice Patrol's 

 increased iceberg detection 

 capability due to the introduction 

 of the AN/APS-1 35 Side-Looking 

 Airbome Radar (SLAR) to ice 

 reconnaisance flights. The 

 impact of SLAR on Intemationai 

 Ice Patrol iceberg detection is 

 examined in Appendix C. 



During the period 2-7 April 

 1984, the Intemationai Ice Patrol 

 participated in an airbome radar 

 iceberg detection evaluation 

 called Bergsearch '84. This 

 experiment was sponsored by 

 the Environmental Studies 

 Revolving Funds (ESRF) 

 administered by the Canada Oil 

 and Gas Lands Administration 

 (COGLA). TheAN/APS-135 

 SLAR was tested along with two 

 APS-94 SLAR's and the two 

 synthetic aperture radars (SAR's) 

 to assess the capabilities of these 

 modem airbome imaging radars in 

 the detection of icebergs in open 

 water. The Ice Patrol conducted 

 71 passes on five sorties over 

 iceberg-infested waters while 

 ground tmth was provided by the 

 MA/ POLARIS and visual 

 confirmations were made by a 

 King Air aircraft. The detection 



data were taken with light to 

 moderate sea conditions of less 

 than 4 meters and included target 

 type (icebergs, sea ice, ships), 

 iceberg size, aircraft altitude, 

 aspect angle relative to the wind 

 (sea), and depression angle. 

 Since the emphasis was placed 

 upon determining the detection 

 of smaller pieces of ice (growlers 

 and small icebergs), the analysis, 

 which was conducted by 

 CANPOLAR Consultants Ltd. 

 under contract to ESRF, dealt 

 with primarily icebergs less than 

 30 meters long. Because the Ice 

 Patrol has been using the new 

 SLAR for two seasons, this 

 evaluation was of considerable 

 interest. Preliminary results 

 indicate that the APS-1 35 SLAR 

 has a detection probability of 

 approximately 65% for 1 0-30m 

 icebergs, and better than 95% for 

 icebergs over 30m in length at 

 sea states moderate and less 

 (Rossiter, 1984). Also, the 

 repeatability of sighting these 

 icebergs fluctuates less than +/- 

 10%. As suspected, the 

 detectability of icebergs appears 

 to decrease with increasing sea 

 state, particularly for smaller 

 targets. For growlers (<100m2), 

 the detection probability is very 

 small (<5%). for they are often 

 substantially submerged, hidden 

 in the sea return or shadowed by 

 the image of a parent iceberg. Of 

 the 2202 icebergs sighted this 

 past season, 83% were small, 

 medium, large, or very large 

 icebergs. Other sightings, which 

 were not visually confirmed, may 

 have been undersized from the 

 SLAR imagery as growlers, since 



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