The determination of slippage of drifters and the leeway of search and rescue targets using InterOcean S4 EMCM

The U.S. Coast Guard Research and Development Center, Improvement of Search and Rescue Capabilities Project has conducted studies of the motion of Lagrangian drifters and search and rescue (SAR) targets relative to the water. This slippage was measured using InterOcean S4 electromagnetic current meters (EMCM), and related to measured winds. The slippage of a FGGE Hull drifter (12 days of slippage data in the Labrador Current) was measured with EMCMs attach above and below the window shade drogue. Preliminary studies have been conducted on a WOCE mixed layer drifter (61.6 hours of slippage data) and a CODE surface drifter (37.4 hours of slippage data). All slippage records show considerable high frequency variability. The FGGE drifter had a slippage of 5 cm/s in 10 m/s wind. The WOCE drifter had slippage of 2 cm/s in 10 m/s of wind. The CODE drifter had a slippage of 0.5 cm/s in 5 m/s of wind. Canadian/US Coast Guard have used EMCM to directly measure the leeway of various SAR targets in winds up to 18 m/s. The SAR targets studied have included 5 and 20 man life rafts, drouged and undrouged, with light and heavy loadings; 5.6 m plank boat, L1011 slide raft, and a enclosed life capsule. Results are currently being assimilated.