An AUV operates independently of the ship and has no connection cables, while ROVs are connected to an operator on the ship.
AUV means autonomous underwater vehicle, so they can be used for underwater survey missions, such as detecting and mapping wrecks, rocks and submerged obstructions. When a mission is completed, the AUV will return to a pre-programmed location where the data can be downloaded and processed.
A remotely operated vehicle (ROV) is an unoccupied underwater robot that is connected to a ship by a group of cables. These cables transmit command and control signals between the operator and the ROV, allowing remote navigation of the vehicle. While there are many uses for ROVs, some of the most common hydrographic applications include object identification and boat hull inspections.