An underwater remotely operated vehicle (ROV) is a mobile robot designed for aquatic work environments. Remote control is usually carried out through copper or fiber optic cables. A human operator sits in a shore-based station, boat or submarine bubble while watching a display that shows what the robot "sees." The operator can also maneuver the robot. Sophisticated underwater ROVs incorporate telepresence to give the operator a sense of being in the place of the machine.
A simple underwater ROV called the flying eyeball has been in military and scientific use for decades. The spherical vehicle lacks robot arms or end effector s but is highly maneuverable. It is equipped with onboard cameras, lamps and thrusters. A launcher containing the robot and its communications cable is dropped from a boat. When the launcher gets to the desired depth, it releases the robot, which is connected to the launcher by a tether. The tether and the drop cable transmit commands to the robot and convey data back to the operator.
The range of remote control for an underwater ROV is limited by several factors. Radio waves in the form of an electromagnetic field do not propagate well through water unless the frequency is so low that the bandwidth is severely limited. Such a restriction on frequency makes high data transfer rates, such as are required for transmission of full-motion video, impossible. The range of direct-beam optical communications systems is limited by lines of sight and the turbidity of the water. It's impractical to have a cable of any type longer than a few kilometers. Some researchers believe that sea mammals, notably whales, communicate underwater over distances of many kilometers using acoustic waves. For this reason, sound and ultrasound have been considered for remote control of underwater ROVs. The main problem with this mode is the low propagation speed, which translates into significant latency over long distances.