was used by the Ice Patrol personnel to help 

 determine if an iceberg report was a new 

 sighting or a resight of an iceberg already 

 being monitored. 



Lenczyk (1964) published a method of 

 predicting the deterioration of icebergs that 

 was used by Ice Patrol up until 1983. The 

 method used sea surface temperature and 

 iceberg size as its inputs to predict, in an 

 average sea state, the number of days for an 

 iceberg to melt. The deterioration was done 

 twice weekly and records for each iceberg 

 were kept by hand. The sea surface tempera- 

 ture was obtained from charts prepared by the 

 U.S. Navy and updates provided by ships 

 reporting sea surface temperature directly to 

 Ice Patrol. This deterioration method was 

 used as input by the Ice Patrol officer to decide 

 to remove an iceberg from the active plot. 



197110 1979 



In 1 971 , Ice Patrol began using a com- 

 puterized version of the manual vector addi- 

 tion routine. The program is described in 

 Morgan (1 971 ). The model area for the com- 

 puterized vector addition routine was selected 

 to cover the area from 40 to 52 degrees North 

 and from 39 to 57 degrees West. At the time 

 of the model creation, it was felt this area 

 would allow modeling of nearly every iceberg 

 that would create a threat to navigation within 

 the area of Ice Patrol's statutory responsibility. 



A computerized version of the monthly 

 currents field was created from the same data 

 Ice patrol had been using as the input to the 

 manual vector addition method. The current 

 fields were updated by Scobie and Schultz 

 (1976) by incorporating recent survey infor- 

 mation into the monthly means. 



FNWC provided a computer-readable 

 wind input for the computer model on a one 

 degree latitude by two degree longitude grid 

 covering the model area. Analysis winds 

 along with predicted winds 1 2 hours, 24 hours, 

 and 36 hours into the future were provided. 

 This allowed Ice Patrol to be able to predict 

 iceberg movement for periods up to 36 hours 

 into the future. 



The computerization of the manual vec- 

 tor addition routine helped eliminate cumula- 

 tive errors associated with hand plotting. The 

 computer also allowed all iceberg reports re- 

 ceived within the model region to have their 

 drift predicted without adding much work load 

 to the Ice Patrol staff. The introduction of the 

 model provided a better tool to determine 

 whether an iceberg sighting report was either 

 a new iceberg or a report of an iceberg already 

 being monitored. This improved ability to 

 model all icebergs and determine if the report 

 was for a new iceberg or not helped improve 

 the accuracy of the estimate made by Ice 

 Patrol of the number of icebergs crossing 

 south of 48 North. Icebergs which were drifted 

 south of 48 North by the model without actually 

 being seen were included in the estimate of 

 icebergs crossing 48 North. 



1979 to Present 



In 1979, the vector addition computer 

 program was replaced by a dynamical bal- 

 ance of forces model (Mountain, 1979). The 

 input procedures, the appearance of the model 

 output, andthe model areadid not change with 

 the model replacement. The winds used as 

 the new model input were supplied by FNOC. 

 The monthly sea current files were combined 

 into a single mean historical current field and 

 used as the current input into the new model 

 (Murray, 1979). In 1981, an addition was 

 made to the model to allow the mean current 

 fieldto be modified by realtime satellite tracked 

 drifter data (Summy and Anderson, 1983). 

 The addition of real time current data allowed 

 the drift prediction model to produce better 

 results. In 1982, a computerized deterioration 

 prediction model was implemented (Ander- 

 son, 1983). The deterioration model allowed 

 the melting of all the icebergs being tracked by 

 IIP to be predicted, not just the icebergs done 

 by hand close to the limits of all known ice. 



During the active season, sighting re- 

 ports received in the area where no model 

 ocean current data exists (along the coast and 

 in the bays of the Newfoundland coast) are not 

 entered into the model. Only a small percent- 

 age of the icebergs reported in the Avalon 

 Channel (the area just off the east coast of 

 Newfoundland) are entered into the model. 

 Icebergs in this area, although south of 48 



59 



