the number of sighting reports in the area of 

 the Hibernia oil field and effected the value of 

 the estimate of icebergs crossing 48 North for 

 those years. 



In 1 989, the sighting source code used 

 for the hydrocarbon industry was renamed 

 "Other aerial reconnaissance." This category 

 now includes iceberg sightings received from 

 the Canadian Department of Fisheries and 

 Oceans (DFO). DFO contracts flights to con- 

 duct reconnaissance of foreign fishing vessels 

 activity on the Grand Banks. The contractor 

 supplies reports of the icebergs and unidenti- 

 fied radar targets seen on each flight to Ice 

 Patrol. The fishing activity is concentrated 

 along the shelf break of the Grand Banks and 

 Flemish Cap, areas of potential high iceberg 

 density. The number of flights conducted by 

 the contractor increased in about 1 991 with a 

 commensurate increase in the number of ice- 

 berg reports. 



The sighting code used by the model 

 was changed in 1989 to accommodate a new 

 source of icebergs. The AES iceBerg Analysis 

 And Prediction System (BAPS) models ice- 

 berg drift in an area to the north of Ice Patrol's 

 model area. AES supplied the predicted posi- 

 tions of those icebergs which were predicted 

 to have drifted across 52 North and Ice Patrol 

 entered them into its model. This particular 

 source did not affect the estimate of icebergs 

 drifting south of 48 north because none of 

 these icebergs reached 48 North prior to 

 either melting or being resighted by another 

 source closer to 48 North. 



Modeling Of Iceberg Drift 



The Ice Patrol models described below 

 were operated only during the portion of the 

 year of iceberg danger. Generally, this would 

 be about one month on both sides of the period 

 when Ice Patrol daily bulletins were issued. 

 This means that reports of icebergs received 

 outside of this period may not have been 

 included in the annual estimate of the number 

 of icebergs crossing 48 North. 



1960 to 1971 



From 1960 to 1971, Ice Patrol main- 

 tained a hand plot of the iceberg's predicted 



motion. Ice Patrol used vector addition of the 

 effects of the wind and sea current on icebergs 

 to predict their motion. The exact origin and 

 basis of this technique was not recorded but 

 was based upon research conducted by Ice 

 Patrol since its inception. 



The wind component vector was com- 

 puted as the downwind direction plus 50 de- 

 grees to the right (to include the effects of 

 coriolis) with a magnitude of drift (in miles/12 

 hour period) of .003684 x W x W + .282 x W 

 (where W = wind speed in knots) (Morgan, 

 1 970). This portion of the drift component was 

 to take into account leeway and the Ekman 

 current component. The coefficients of the 

 equation were adjusted over the years. The 

 above coefficients are from the late 1960s. 



The wind data for the vector addition 

 routine was obtained from the U.S. Navy Me- 

 teorological office at Argentia until the closure 

 of Air Station Argentia in 1 970. After 1 970, the 

 wind data was supplied by the U.S. Navy Fleet 

 Numerical Weather Center (FNWC) in 

 Monterey, the predecessor of the Fleet Nu- 

 merical Oceanographic Center (FNOC). 



The ocean current information was 

 derived from two sources. Ice Patrol con- 

 ducted hydrographic surveys in the vicinity of 

 the Grand Banks beginning shortly after the 

 inception of Ice Patrol and developed geostro- 

 phiccurrent data using the methods described 

 in Sverdrup et al., 1942. Monthly mean dy- 

 namic heights forthe area of the Grand Banks 

 were developed (Soule, 1 964). The U.S. Navy 

 OceanographicOffice monthly mean charts of 

 sea current were used to provide information 

 for the area outside of that covered by the Ice 

 Patrol mean dynamic height charts. The sea 

 current was vectorially added to the wind com- 

 ponent to predict iceberg drift. 



With a manual plot method, there was 

 a practical limit to the time available to predict 

 the drift of icebergs upstream of the icebergs 

 closest to the area defining the limit of all 

 known ice. During light iceberg years, it was 

 possible to predict the drift of all of the icebergs 

 reported to Ice Patrol. During a heavy iceberg 

 year, it may have been impractical to predict 

 the drift of all the reported icebergs. The 

 manual plot was updated twice daily. The plot 



58 



