Data processing and performance testing of a low-cost surface drifter design for use in coastal waters

A surface drifter design suitable for deployment in the Gulf of Finland is presented. The drifters were designed for deployments lasting several weeks, and used a GPS/GPRS tracker unit to transmit drifter coordinates at a sampling frequency of 10-15 min. The drifter design was modified during the deployment period 2010-2014, which increased the lifetime and reliability of the track recording and reduced the direct wind drag impact, but did not significantly alter the current following performance of the drifter. A novel data quality control scheme was developed, where a time-varying reference speed derived from the data was used to identify data outliers. Compared with traditional quality control methods that use a constant reference speed limiter, the method presented here limits both the local maximum and local minimum drifter speed and is capable of identifying local extrema in relatively low drifter speed regimes.