autonomous underwater vehicle

An autonomous underwater vehicle, or AUV, is a robot submarine that swims through the ocean on its own, with no cable tying it to a ship and no human steering it moment to moment. You give it a mission ahead of time — survey this stretch of seabed, follow this depth, take these measurements — then it dives, carries the plan out alone for hours or days, and surfaces to hand back what it found. This makes it different from a tethered ROV (remotely operated vehicle), which is flown live by a pilot through a long umbilical cord; the AUV cuts that cord and trades constant control for true independence and far greater range.

Two everyday problems become surprisingly hard once a robot goes underwater. The first is simply staying at the right depth: a body in water floats or sinks depending on its buoyancy, the balance between its weight and the upward push from the water it shoves aside, so an AUV carefully tunes that balance and uses fins, propellers, or thrusters to drive forward and steer, much as a fish uses its body and tail. Some gliders even save power by changing their buoyancy to sink and rise in long, slow zig-zags, barely running a motor at all. The second problem is power and shape: it must carry its own batteries and resist the crushing squeeze of deep water, so AUVs tend to be sleek, sealed tubes built to slip through the sea efficiently.

The hardest problem of all is knowing where it is, because the satellite signals that guide cars and drones — GPS — do not travel through seawater. Cut off from that, an AUV must navigate almost blind: it tracks its own speed and heading to estimate how far it has moved, listens to sound bouncing off the seabed, and sometimes triangulates off underwater sound beacons, because radio is useless and light reaches only a few metres in murky water. Despite all this, AUVs map the seafloor, inspect pipelines and undersea cables, hunt for shipwrecks, monitor pollution and sea life, and survey under polar ice where no crewed vessel can safely go.