Let's Dissect a Drifter
What is a drifter?
A modern drifter is a high-tech version of the “message in a bottle.” It consists of a surface float and a drogue (sea anchor), which are connected by a long tether.
Drifters average their data across a window in time, then transmit these data to an orbiting satellite.
Each drifter transmitter is assigned a unique code, referred to as the drifter ID, which makes the identification of each drifter possible.
Surface Float
The surface float ranges in size from 30.5cm to 40cm in diameter and contains approximately 4 battery packs (each with 7-9 alkaline d-cells), a satellite transmitter, a thermistor to measure sea surface temperature, a tether strain to verify the presence of the drogue; and other possible sensors to measure barometric pressure, salinity, waves, and/or wind speed and direction.
For an in-depth view of the surface float, along with the function of its components, reference the image to the left.
Tether
The surface float and the drogue are connected by a long (approximately 12.2 meter) impregnated wire rope, which is designed to minimize corrosion and extend the overall time the drifter transmits data with its drogue attached.
Drogue
The drogue (also called a sea anchor) is centered at a depth of 15 meters beneath the sea surface to measure currents in the upper ocean. The drogue is designed to minimize the effect of the wind and waves on the surface float, by anchoring the drifter in the upper ocean layer.
