Autonomous Underwater Vehicles AUVs
Unlike ROVs, Autonomous Underwater Vehicles are capable of functioning without real-time control from a human operator. They can be programmed to collect data along a predetermined route, and some are able to make decisions and potentially change their mission parameters according to the received data.
Due to the attenuation of radio waves in water, AUVs cannot rely on direct GPS navigation once submerged. Dead reckoning can be used to establish an estimate of position, although errors compound quickly. This positional estimate can be further improved by additional data from underwater acoustic transponders, GPS positions of nearby surface references, or temporary surfacing to establish a GPS fix. Acceleration and velocity estimates can be calculated using an Inertial Measurement Unit, and improved with a Doppler Velocity Log, a device similar to sonar which measures the rate of travel over the sea floor.