A performance comparison for two lagrangian drifter designs

Abstract

Abstract We compare the water‐parcel‐following and position‐reporting performance of two recent drifter designs. One (Tristar‐II ) uses the ARGOS satellite navigation system, has a very large drogue: float frontal area ratio and a small velocity error resulting from wind drag and surface wave forces. The second design uses an internal Loran receiver and transmits its position every half hour by radio. Its drogue: float frontal area ratio is much smaller than the TRISTAR's; we wished to know if this difference caused a significant change in drifter trajectory. Over a 78‐h joint deployment, the two designs had nearly identical trajectories. Measured drift speeds ranged from 10 to 30 cms−1. Wind speeds (an important potential biasing factor) ranged up to 15 ms−l. Net velocity difference over the full deployment was only 0.1 cms−1. Frontal trapping of both drifters during the latter part of the comparison period may have helped to minimize this difference. But we also observed little or no downwind slippage (...