The purpose of deploying BTT's was to make 

 current measurements to compare with the IIP 

 current file. To do this BTT positions were first 

 input to a computer program utilizing a cubic 

 spline routine to smooth out the drifts. The 

 program calculated a smooth trajectory by 

 ensuring a mathematically continuous first 

 derivative of the BTT displacement versus time 

 plot, thus velocity, and a minimum second 

 derivative, thus acceleration or potential energy. It 

 then output a printout of 6-hourly BTT positions 

 and velocities (Table 2) and a plot of the smooth 

 BTT trajectory (Figures 3-7) representing an 

 approximation of the path the BTT followed. On 

 these plots X's represent input positions, not all of 

 which are marked, and numbers are Julian dates. 



To make valid comparisons with the IIP cur- 

 rents, the wind current's contribution must be 

 removed from the BTT drifts. Another program, a 

 modified version of IBERG, used CIIP wind files to 

 calculate wind currents using the same Ekman 

 equation described earlier. The actual comparison 

 of observed drifts and IIP currents was 

 accomplished by a third program (Table 3). It 

 computed 6-hourly observed currents with the 

 wind current subtracted out (BTT w/o W.C.) and 

 then vectorially subtracted the IIP (normal) 

 current from this value. The difference was output 

 in individual and cumulative speed and direction 

 and U (east-west) and V (north-south) components 

 on a printout and plots. The results were then 

 analyzed to determine what if any changes in the 

 current file were warranted. Magnitudes of 

 differences, variability of currents in the respec- 

 tive location, time of season and reliability of 

 measurements were among the items taken into 

 account. No changes to the IIP current file were 

 made during the 1979 season. 



REVIEW AND OUTLOOK 



The validity of the concept of using satellite 

 tracked BTT's to measure currents was proven 

 during the 1979 season. Even though the system 

 was in its fledgling stages, it worked well enough 

 to determine if changes to the IIP current file were 

 necessary. 



Programs developed to analyze the BTT drifts 

 proved adequate. Much was learned about the 

 capabilities and limitations of the system. Several 

 refinements are planned for the 1980 season but 

 the general overall operational scheme will remain 

 the same. Perhaps most significantly, since the end 

 of the 1979 season a second satellite in the TIROS 

 series, NOAA-6, has been launched and is opera- 

 tional. It will provide additional positions and 

 thereby even more accurate evaluation of IIP 

 currents. Additionally, several reference beacons 

 have been procured for use to ensure maximum 

 accuracy is obtained. Overall, during 1979 the 

 satellite tracked buoy system provided more 

 accurate and much more timely current 

 measurements at a reduced cost as compared to 

 the old survey method. With the system still 

 developing the prospects for the future appear 

 even brighter. 



REFERENCES 



Scobie, R. W. and R. H. Schultz (1976). Oceanography of 

 the Grand Banks Region, March 1971-December 1972. 

 U.S. Coast Guard Oceanographic Report No. 70, Coast 

 Guard 373-70:47. 



Soule, F. M. (1964). The Normal Topography of the 

 Labrador Current and its Environs in the Vicinity of 

 the Grand Banks of Newfoundland during the Iceberg 

 Season. Woods Hole Oceanographic Institution, Ref. 

 No. 64-36. 



Buoy ID 



2605 

 2602 

 2600 

 2601 

 2604 



Date 



01 March 

 05 April 

 12 May 

 04 June 

 04 June 



NOTE: Latitude and Longitude are in degrees-minutes. 



B-3 



