AUV

An autonomous underwater vehicle carries its own power and makes its own decisions. There is no tether, no pilot, and for most of a mission no contact with the surface at all, because seawater blocks the radio frequencies that carry satellite positioning and data links. The vehicle is given a mission plan before launch, executes it, and surfaces or docks to hand over what it recorded. That one difference from a remotely operated vehicle changes almost everything about the design.

Endurance and navigation are the hard problems. Endurance is set by battery chemistry, the hotel load from sensors and processors, and hydrodynamic efficiency, which is why the classic survey vehicle is a torpedo shape flying a straight line at a steady few knots rather than hovering. Navigation without satellites depends on dead reckoning: an inertial measurement unit integrated against a Doppler velocity log that measures speed over ground acoustically, with depth from pressure and heading from a gyrocompass. Position error grows with distance travelled, so missions are bounded by acceptable drift and corrected by surfacing for a fix, by acoustic ranging to a surface vessel or seabed transponders, or by matching observed terrain against a known bathymetric map.

Form follows mission. Survey vehicles carry synthetic aperture or multibeam sonar and sub-bottom profilers, and they trade manoeuvrability for range. Hovering vehicles use vectored or multi-axis thrusters to inspect structures closely, giving up endurance for control. Gliders change buoyancy instead of using propulsion, sawtoothing through the water column for weeks at very low speed, and suit oceanographic sampling rather than high-resolution imaging. Sizes run from man-portable units to vehicles that need a dedicated launch and recovery system.

The buyer questions are practical. What depth, what sensor payload and how much data it produces, how many hours at survey speed, what navigation accuracy holds over that duration, how the vehicle is launched and recovered in realistic sea states, and what the recovery plan is when it does not surface on schedule.