Contents I. Introduction
In recent years, the research and applications of underwater robots have become an area of increasing interest to tap aquatic resources [1]–[4]. Many obstacles associated with underwater inspections, such as physical risk and accessibility, have made many tasks incredibly hard for human inspectors or divers. As a result, underwater robotics have arisen as an effective tool for inspection. Two types of vehicle are available. One is a manned vehicle, and the other is an unmanned one [1], [5]–[7]. A manned vehicle may weigh 20 tonnes, including life-support systems and limited capacity for documentation [5]. So, we prefer unmanned vehicles for research work. Unmanned underwater vehicles (UUVs) are generally classified as remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs) [1], [7], [8]. An ROV is usually controlled by a tether from a ship or a boat and is used for various tasks, ranging from inspection to intervention. On the other hand, AUVs are used for inspection works and can operate independently underwater for a period of time depending on the battery’s capacity [7], [8]. Underwater operations pose additional challenges for researchers and developers, as underwater systems require additional [4] environmental conditions and networking, particularly when working in the open sea. Such equipment must include watertight electronics at deep, materials resistant to corrosion, the ability to navigate without the use of traditional methods of communicating (such as GPS or WiFi) [9]–[11], etc. Figure 1 shows the pictorial view of an ROV and an AUV in underwater.
