Another basin-scale sonar research project uses drifting sources (Rossby et al. 1986), called SOFAR or
RAFOS floats. These devices drift at depth and periodically emit a high-intensity tone (195 dB re 1µPa @ 1
m) that is frequency swept at 200-300Hz or a CW signal at 185-310 Hz with durations of 120 sec or more.
The sounds are detected at distant receivers and their timing is used to determine the float location and
therefore its drift, as a proxy for deep currents.