Using the above philosophy as the basis of 

 accomplishing its mission, Ice Patrol does not 

 and has never attempted to conduct a com- 

 plete census of the icebergs or survey the 

 whole of the Grand Banks for icebergs. The 

 presence or absence of icebergs in areas 

 removed from the extreme limits of the region 

 of iceberg danger does not affect the perfor- 

 mance of the Ice Patrol mission. Generally, 

 areas of the Grand Banks removed from the 

 limits of iceberg danger can have significant 

 concentrations of icebergs and because of the 

 nature of the mission, the icebergs located 

 there may not be included in the data set. 



Iceberg Data Collection 



The traditional measure of an iceberg 

 season's severity is the estimate of the num- 

 ber of icebergs drifting south of latitude 48 

 North. The methods used to collect and ana- 

 lyze the data has changed over the years. In 

 addition to changes in methods, a variety of 

 factors affect the accuracy of the estimate 

 published each year. These include the use of 

 numerical models, the severity of the season 

 itself, reconnaissance techniques and techno- 

 logical advancements, subjectivity caused by 

 change in personnel, and navigation accu- 

 racy. A summary of the technological changes 

 is included in Attachment 1 . These factors will 

 be discussed in more detail below. 



The reason for selecting 48 North as 

 the boundary at which to begin counting ice- 

 bergs is tied to the great circle shipping routes 

 from Europe to America. The great circle route 

 from the English Channel to New York would 

 pass through the island of Newfoundland so 

 the routes used had a turn point off Cape 

 Race, the southern point of Newfoundland. 

 Cape Race is located at about 46 degrees 35 

 minutes North. Early reports of the Interna- 

 tional Ice Patrol Service (priorto 1 926) referto 

 icebergs south of Newfoundland. Mecking 

 (1907) collected data from U.S. Signal Ser- 

 vice, U.S. Hydrographic Office and the 

 Deutsche Seewarte (the German Hydrographic 

 Office) and published the first estimate of 

 icebergs for the period 1880 to 1897. Smith 

 (1926) continued the analysis and published 

 the estimate of icebergs for the period 1 898 to 

 1 926 and used the 48th parallel as the north- 

 ern point of his analysis. IIP has published the 



yearly estimate of icebergs drifting south of 48 

 North in the annual Reports of International 

 Ice Patrol Service ever since (Figure 1 ). 



Presently, International Ice Patrol does 

 not include sighting reports of growlers or 

 radar targets in the estimate of the number of 

 icebergs drifting south of 48 North. Radar 

 target reports (targets which cannot be identi- 

 fied) come from a variety of sources including 

 ships and aircraft. Therefore, this paper does 

 not include radar targets or growlers as part of 

 the discussion. 



General 



The present Ice Patrol operations area 

 is bounded by the area 40 to 52 North and 57 

 to 39 West (Figure 2). Ice Patrol's statutory 

 mandate requires Ice Patrol to define the limits 

 of the dangerous region, not survey the entire 

 area where icebergs might exist. Ketchen 

 (1 977) provides a synopsis of icebergs sighted 

 well outside of the Ice Patrol operations area. 

 Although these are dramatic sightings be- 

 cause of their extraordinary location, they rep- 

 resent only a small fraction of the icebergs 

 seen in most years. 



The area encompassed by the limit of 

 the iceberg danger fluctuates on a season to 

 season basis and also within a season. Tradi- 

 tionally, the portion of the Ice Patrol operations 

 area enclosed by the limit of iceberg danger is 

 largest during the months of April through 

 June within each season. There have been 

 seasons where the area of iceberg danger has 

 extended south of 40 North, the southern 

 border of Ice Patrol's normal operations area. 

 When this occurs, Ice Patrol's reconnaissance 

 efforts are concentrated in the southern area 

 because Ice Patrol is not able to use the 

 available model to predict the movement of 

 icebergs in this area. This last occurred in 

 1989. 



The available reconnaissance flights 

 are first used to fly the edge of the area of 

 iceberg danger (where the iceberg concentra- 

 tion is low) to accurately define the limits of 

 iceberg danger. The more available flight time 

 spent in transit to reach extended limits, means 

 proportionally less of the limit of iceberg dan- 

 ger that can be covered per flight. Therefore, 



50 



