North, do not effect the limits of the area of 

 iceberg danger. The total number of iceberg 

 sighting reports received and not entered into 

 the model for this area (and therefore the data 

 base) is unknown. 



Analysis Techniques Of 

 Siaiiting/Drift Data 



All iceberg sighting data received by 

 Ice Patrol is treated the same regardless of 

 sighting source. After a sighting report is 

 received, Ice Patrol personnel must determine 

 whether the report is for a new iceberg or a 

 resight of an iceberg already reported. The 

 reported position is compared to the predicted 

 positions of previously reported icebergs. 



The criteria for determining whether a 

 sighting report is a resight or not have changed 

 over the years and also vary by geographic 

 position within the Ice Patrol area and with 

 proximity to the limits of all known ice. The 

 criteria described below are the general prin- 

 ciples used from 1 960 to 1 991 . 



If the report is in an area known to have 

 variable currents (particularly near the Tail of 

 the Banks), a sighting report within about 30- 

 40 miles (depending upon when the iceberg 

 was last reported) of the predicted position of 

 a previous report could be considered a resight. 

 Icebergs further from the limits 

 of all known ice are more likely to be resighted, 

 particularly those on the northern portion of 

 the Grand Banks. 



As the "Limits of all known ice" are 

 approached, a more conservative approach to 

 resights is taken. Unless the sighting report 

 closely approximates the predicted position 

 and size of a previous report, the iceberg is 

 added rather than resighted. This philosophy 

 ensures all of the icebergs near the limits of all 

 known ice are reported in Ice Patrol's prod- 

 ucts. 



There are four ways icebergs are re- 

 moved from the list of active icebergs being 

 monitored by Ice Patrol. If an Ice Patrol flight 

 overflies the location of an iceberg and the 

 iceberg is not located, the iceberg will be 

 deleted from the active iceberg list. If the 

 iceberg is predicted to have melted, it will be 



removed from the active list. A more conser- 

 vative approach to removing icebergs because 

 of melt is applied when the iceberg is close to 

 the limits of all known ice. If an iceberg has 

 been on the active list for thirty days without 

 been resighted, it will be removed. If an 

 iceberg is predicted to drift to the east or west 

 of the Ice Patrol area, it will be removed from 

 the list of active icebergs and a note about the 

 last predicted position will be put in the iceberg 

 bulletin sent to shipping. 



Icebergs are not removed from the ac- 

 tive list when a ship report of no ice in an area 

 is received because the errors associated with 

 the drift prediction could easily have placed 

 the iceberg outside the detection capability of 

 the ship. 



"Counting" Tlie Icebergs 

 South Of 48 North 



From 1960 to 1988, the estimate of 

 icebergs crossing south of 48 North was deter- 

 mined by hand counting from the paper records 

 and/or model outputs. The Ice Patrol officer 

 was responsible for determining the estimate 

 of the number of icebergs crossing 48 North , a 

 task that was easier in light ice years than 

 during heavy years. 



1960-1970 



Atechnician was assigned to keeptrack 

 of the number of iceberg sightings that were 

 reported south of 48 North. Icebergs that were 

 predicted to drift south of 48 North were also 

 included. In heavy ice years, not all of the 

 icebergs reported may have had the manual 

 drift done. The numbers produced by the 

 technician were reviewed by the Ice Patrol 

 officer prior to release. 



1970-1988 



Forthe computer model years, the tech- 

 nician would review the daily model printouts 

 each month and determine which icebergs 

 had either been sighted or drifted south of 48 

 North. No differentiation was made between 

 icebergs sighted and those drifted south of 48 

 North (without actually being seen south of 48 

 North). For each iceberg south of 48 North, 

 the technician would have to determine how 



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