Autonomous velocity and density profiler: EM-APEX

We developed an autonomous ocean profiling velocity and density float that provides exceptional vertical coverage and temporal resolution to depths of 2000 m for deployments of many years. Electrodes were added to the exterior of standard WRC APEX floats, and electronics were added inside. The electrode voltages result from the motion of seawater and the instrument through the Earth's magnetic field. Other systems included magnetic compass, tilt, CTD, GPS, and Iridium (providing sampling/mission changes). Three EM-APEX floats were deployed from a C-130 aircraft ahead of Hurricane Frances. The floats profiled for 10 hr from the surface to 200 m, then continued profiling between 30 m and 200 m with excursions to 500 m every half inertial period. The velocity computations were performed onboard and saved for later transmission. After five days, the floats surfaced and transmitted the accumulated processed observations, then the floats profiled from 500 m every half inertial period until recovered early in October located by GPS and Iridium.