APPENDIX B 

 ICEBERG DRIFT FROM SURFACE CURRENTS 



by Dr. J. P. Welsh, Jr, and LT S.M. Phillips, USCG 

 (U.S. Coast Guard Research and Defelopment Center) 



Introduction 



The operational requirements of the International Ice Patrol 

 (IIP) are to locate Icebergs that menance the North Atlantic 

 shipping lanes off the Grand Banks of Newfoundland and to 

 predict their movement. A computerized Iceberg drift model 

 has been developed to assist In the performance of these 

 requirements. This model, developed from first principles and 

 checked with observational Iceberg drift data, will produce 

 relatively precise positions when supplied with precise values 

 of current, wind velocity. Iceberg mass, drag coefficients, 

 values for sail area, and Immersed cross section area. 



The objective of this Iceberg drift study was to determine 

 by field tests the usefulness of an expendable surface current 

 probe for determination of Iceberg drift as It applies to IIP 

 needs. This recently developed alr-deployable device measures 

 surface current precisely, rapidly, and inexpensively. 



The method of determining the surface current is Illustrated 

 in Figure 1. An expendable probe is launched, and on contacting 

 the sea surface a surface marker (SM in Figure 1) separates and 

 floats on the surface. This serves simply to mark the location 

 of the measurement. The remainder of the probe is carried to 

 the bottom by its weight and from its fixed location on the 

 bottom, releases two floats (marked Fl and F2 in Figure 1) 

 with a predetermined time delay between them. The floats return 

 to the surface by their own buoyancy. At the surface these 

 floats emit fluorescein dye to aid in visual location on the 

 surface. The surface current and direction are obtained by 

 the following relationships. 



„ - ^ Separation of Fl and F2 



Surface current = ~—^ r—z ; — ; 



Time delay between float releases 



Surface current direction = direction from F2 to Fl 



(Brolda and Richardson, 1972) 



B-1 



