Table 4. Final NSSI Rating Categories 



The percentiles were used as guides to create the rankings for light, moderate, heavy, and extreme years, 

 but they were not the deciding factor. The averages for each variable and frequency of occurrence were 

 taken into account to create a more accurate representation of season severity. 



Comparison of NSSI to Previous Standards 



Most recently. Trivers (1994) updated the International Ice Patrol's season severity classification based on 

 the number of icebergs that passed south of 48°N during a season. Trivers based his data upon Alfultis 

 (1987) results on season severity, but tried to take into account the difference in iceberg data collection 

 methods. He examined the difference between the pre-SLAR (Side-Looking Airborne Radar) years and the 

 SLAR years. In the pre-SLAR years. Trivers notes that an extreme year in the terms that Alfultis set are 

 average under SLAR years. This difference could be the result of either better detection due to increased 

 technology or natural variations in iceberg counts and distribution. If the increase is due to technology, 

 then this may have an effect on the results of the NSSI, however Trivers found that the pre-SLAR years 

 had not been undercounted. Trivers created new iceberg population severity classes as shown in Table 5. 

 By comparing these severity classes by the data used for the NSSI. the severity classes used by Trivers 

 seem to be low compared to the NSSI data. The average number of icebergs below 48 "N was 702 for NSSI 

 years whereas in Trivers the extreme year was classified as 600 plus icebergs. Using Trivers" ( 1994) 

 standards to classify the NSSI data. 13 of the 27 years would have been classified as extreme, whereas 

 using NSSI rankings, only 4 years were classified as extreme. 



Table 5. Trivers ( 1994) Severity Classes 



Conclusion 



The NSSI rating combines the three most important variables into a single number that indicates of the 

 severity of an iceberg season: LAKI area. LOS and the number of icebergs that passed south of 48''N. 

 The previously used indicator, the number of icebergs south of 48^N. provided information only on the 

 number of icebergs that entered the shipping lanes, without regard to how far they spread or how long they 

 persisted. The NSSI focuses on the severity of an iceberg season from the standpoint of the transatlantic 

 mariner. IIP"s most important customer, because it represents the areal and temporal extent of the iceberg 

 threat during a given season. 



The NSSI is also a good indicator of the effort required for IIP to provide its services during a season. A 

 season with a large number of icebergs concentrated near the Grand Banks is far less challenging than a 

 season with a smaller number of widely distributed icebergs. The most important result of a wide iceberg 



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