What is a Profiling Float?

Profiling floats evolved from the ALACE float concept. ALACE floats were originally conceived by Doug Webb of Webb Research. The need for such a device followed the successes of the SOFAR and RAFOS float systems which, though they supplied enormously valuable data, were restricted to areas of the ocean with acoustic sound sources or listening devices available. The ALACE concept aimed to supply a float that operated autonomously and could operate anywhere (except in ice-infested waters). ALACE is an acronym standing for, Autonomous LAgrangian Current Explorer. Much subsequent development was completed cooperatively with Russ Davis' group at the Scripps Institute of Oceanography, particularly adding the "P" to turn an Alace into a P-Alace float - a Profiling ALACE float.

The Alace float is launched at sea, adjusts its buoyancy to sink to a preprogrammed depth where it remains for a preprogrammed period. It then readjusts its buoyancy, floats to the surface and is positioned by satellite.

Soon after Alace floats were first launched the idea naturally arose that the floats should be equipped with instrumentation to observe temperature on the way up, and then later salinity was added. A variety of sensors have been tried, at the present time most of the community that uses profiling Alace floats (or P-Alace floats) are using a device equipped with a Seabird CTD.

The instruments sample temperature and salinity in during the ascent phase of their cycle and transmit the data to a satellite run by Service Argos. The data stream includes messages describing the CTD profile, and position information allowing tracking at the surface.

The float completes its duty cycle by re-adjusting its buoyancy and sinking once again to its pre-programmed depth. The latest version of the P-Alace float produced by Webb Research is powered by alkaline batteries, and has power sufficient to execute about 200 profiles. This is a re-engineered version that has been given a new acronym, APEX, which is "Autonomous Profiling EXplorer". Another version is the PROVOR float, built by Metocean in Dartmouth, N.S. and Martec, in France.

More information about P-Alace floats, or APEX floats, can be obtained at the Webb Research web site. In particular I suggest visiting their list of links, especially to the site run by Steve Riser displaying his P-Alace float data. That link is also here .