CODE Drifter


SVP Drifter Schematic
CODE drifter with Salinity sensor installed

Technical Description

  • GPS based tracking
  • Iridium Short Burst Data (SBD) telemetry
  • Sea Surface Temperature (BTO)
  • Sea Surface Salinity (BTO)
  • Directional Wave Spectrum (BTO)
  • Variable sampling rate down to 5 minutes

Hardware

The CODE drifter (Davis 1985) was designed as an inexpensive water follower to track currents in the upper meter of the oceanic mixed layer. However, as of today, the cost of a CODE and SVP drifters similar. The CODE drifter consists of a cylindrical hull, 10-15 cm in diameter, that contains the batteries and electronics. The drag element consists of four sails made of plasticized nylon arranged in a cross-like shape. The CODE drifter is slightly negative buoyant and four small floats connected to the end of the arms to which the sails are attached provide the extra buoyancy to ensure floatation.

The CODE drifter is considered an accurate water follower and laboratory wave tank test have shown that, if the drifter stays upright, the slip through the surrounding water is of the order of 1 cm/s for moderately sized waves (Davis 1985). However, it is likely that in presence of large breaking waves the drag of the submerged part is affected by substantial tilting of the buoy, thus resulting in possible rectification of the relative motion of the drifter with respect to the wave orbital velocity. Poulain et al. (2009) have found that the CODE drifters measure a wind induced Ekman Current that is approximately directed at 28°-30° to the right of the wind (in the northern hemisphere). This is much less than the 45° angle predicted by the Ekman theory (e. g. Gill 1982) and closer to the angle found for undrogued SVP drifters, which is generally more downwind, at about 17°—20° to the right of the wind. This suggests that the CODE drifter may be subject to more wave—induced downwind leeway than the SVP drifter.

The lifespan of the CODE drifter is about one year.

Electornics

Heart of the CODE drifter is the LDL buoy controller, enabling a number of sensor payloads. The basic sensor suite includes a GPS engine and SST but ancillary Sea Surface Salinity measurements are also available.

Air Deployment Ready

Self deploying air deployment vehicle packaging and rigging is available.