Autonomous Velocity and Density Profiler: EM-APEX
Thomas B. Sanford1, John H. Dunlap1, James A. Carlson1, Douglas C. Webb2
(206) 543-1365 and Sanford@apl.washington.edu
1
Applied Physics Laboratory, University of Washington, Seattle, WA 98105 USA
2
Webb Research Corporation, E. Falmouth, MA 02536
We developed an autonomous ocean profiling velocity and density float that provides
exceptional vertical coverage and temporal resolution. Electrodes were added to the exterior of
standard WRC APEX floats, and electronics were added inside. The electrode voltages were
interpreted in terms of the motion of seawater and the instrument through the Earth’s magnetic
field. Other systems included magnetic compass, tilt, CTD, GPS and Iridium. Three EM-APEX
floats were deployed from a C-130 aircraft about 1-day ahead of Hurricane Frances. The floats
profiled for 10 hours from the surface to 200 m with a single traverse to 500 m, then continued
profiling between 35 and 200 m with excursions to 500 m every half inertial period. The
velocity computations were performed onboard and saved for later transmission. After 5 days
the floats surfaced and transmitted the accumulated processed observations, then the floats
profiled to 500 m every half inertial period until recovered early in October aided by GPS and
Iridium.
Most appropriate session: Lagrangian Drifters and Floats
Alternative sessions: Measurement from UUVs OR Mechanical and Electromagnetic
Instruments
Key words: ocean velocity, autonomous velocity profiler, APEX floats, motional induction,
ocean electrodynamics