Underwater glider

At a certain depth, the glider switches to positive buoyancy to climb back up and forward, and the cycle is then repeated.

[1] The typical up-and-down, sawtooth-like profile followed by a glider can provide data on temporal and spatial scales unattainable by powered AUVs and much more costly to sample using traditional shipboard techniques.

[3] The sawtooth glide pattern, stealth properties and the idea of a buoyancy engine powered by the swimmer-passenger was described by Ewan Fallon in his Hydroglider patent submitted in 1960.

[4] In 1992, the University of Tokyo conducted tests on ALBAC, a drop weight glider with no buoyancy control and only one glide cycle.

The University of Washington Seaglider, Scripps Institution of Oceanography Spray, and Teledyne Webb Research Slocum vehicles have performed feats such as completing a transatlantic journey[7] and conducting sustained, multi-vehicle collaborative monitoring of oceanographic variables.

They were initially designed to quietly track diesel electric submarines in littoral waters, remaining on station for up to six months.

By 2012, a newer model, known as the ZRay, was designed to track and identify marine mammals for extended periods of time.

[13][14] Since they are propelled by a buoyancy engine, gliders have moving parts that are only active occasionally, so there are minimal mechanical vibrations and noise, making them excellent vehicles for sensitive instrumentation including microstructure probes[15] and acoustic sensors.