History ++++++++++++ The following text is from `Seaglider_Pilot's_Guide `_ document since it's the best summary I have found about the history of underwater gliders. The history of buoyancy-driven oceanographic instruments begins with Archimedes (287 BCE - 212 BCE). Archimedes's life began and ended in Syracuse, Sicily, but he was educated and spent part of his life in Alexandria, Egypt. He is generally regarded as one of the three greatest mathematicians of all time (Newton and Gauss complete the triumvirate) and is considered the father of hydrostatics, static mechanics, and integral calculus. Archimedes's Principle, the most well known of his hydrostatic results, is the basis for all buoyancy-driven vehicles. It states that the buoyant (upward) force on a submerged object is equal to the weight of the fluid that is displaced by the object. This fact is used in the variable mass, fixed volume (ballast) control systems of modern submarines and submersibles, and in the fixed mass, variable volume control systems of small profiling oceanographic instruments. The use of buoyancy control in oceanographic instruments dates from the mid-1950's. By 1955, Henry Stommel of the Woods Hole Oceanographic Institution and John Swallow in the United Kingdom had ideas for neutrally buoyant floats whose positions could be tracked acoustically. Swallow was the first to build such a device, which contained a free-running 10kHz acoustic source and was tracked from a surface ship. By the 1970's, transponding versions running at 3-4kHz had extended shipboard detection ranges to 50 km, and a 200Hz version used the Sound Fixing and Ranging (SOFAR) sound channel (Stommel's original idea) to remove the requirement for ship-based tracking. By the 1980's, Tom Rossby at URI had developed the inverse of the SOFAR float (called RAFOS, SOFAR spelled backwards) that relied on moored sound sources and an acoustic receiver on the float. By adding a compressee (an object whose compressibility is approximately the same as that of seawater), these floats could also be ballasted to follow a particular density surface, rather than a pressure surface. About the same time, John Dahlen's group at Charles Stark Draper Laboratory developed a moored profiler that used a variable buoyancy device to propel itself up and down along the mooring wire, measuring temperature, conductivity and currents. .. image:: /images/Stommel.png In the 1990's, Russ Davis and his group at Scripps Institution of Oceanography added a variable-buoyancy device to a neutrally buoyant float to create profiling floats. These floats (called Autonomous Lagrangian Current Explorers, or ALACE) had the ability to inflate an external bladder, thereby changing their displaced volume, but not their mass. The resulting buoyancy force allowed the float to make profile measurements from its neutrally-buoyant depth to the surface. At the surface, position and profile data were transmitted via the Service ARGOS satellite system. By the year 2000, hundreds of this type of float were deployed worldwide, both of the Scripps design and a design from Webb Research Corporation of Falmouth, Massachusetts. Gliders share a common heritage: Henry Stommel's vision, published in 1989 in Oceanography [Stommel, 1989]. Stommel imagined a fleet of vehicles that "...migrate vertically through the ocean by changing ballast, and they can be steered horizontally by gliding on wings. During brief moments at the surface, they transmit their accumulated data and receive instructions. Their speed is about 0.5 knot." A prototype gliding vehicle was fielded as early as 1991 by Webb Research Corporation (WRC). This vehicle demonstrated the basic configuration subsequently used by all three gliders. A few years later, the ONR-sponsored Autonomous Ocean Sensing Network (AOSN) program, led by Tom Curtin, sponsored three groups to develop autonomous underwater gliders: Webb Research Corporation, whose glider is called Slocum, a team of Scripps Institution of Oceanography (Russ Davis) and Woods Hole Oceanographic Institution (Breck Owens) who developed Spray, and the University of Washington (Charlie Eriksen) who developed Seaglider. All groups worked with similar design goals: small enough to be handled by two people, relatively low acquisition and operation costs, horizontal speeds of around 30 cm/s, endurance of up to a year, GPS positioning and two-way data telemetry at the surface, and basic sensor payloads, including a CTD. By the year 2000, all groups had operational models that addressed these design goals.