Detecting the drogue presence of SVP drifters from wind slippage in the Mediterranean Sea

The Surface Velocity Program drifter data, collected in the Mediterranean Sea since 1989, are analysed in order to evaluate and, possibly, improve the accuracy of the drogue (sea anchor, attached to the buoy by a long thin tether) presence detection system. Wind products and altimetry data are used to estimate the wind slip from the drifter velocities. Complex correlations between the drifter residual and wind velocities reveal potential errors of the SVP drogue detection system and allow to define the drogue status for drifters without information about the drogue presence. A simple procedure is applied to update the drogue status by matching the drogue detection system data and the wind slippage correction. This method allows assigning a drogue status to about 88% of the drifter observations which were lacking this information and to detect/correct anomalous behaviours of the drogue detection system in 5.2% of the analysed cases.