An Overview of Underwater Robotics Technology

 Underwater robotics has become an essential field, enabling a wide variety of marine operations, from exploration to industrial and research activities. These robots, typically referred to as remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs), are outfitted with advanced sensors, cameras, and manipulation tools that allow them to operate in deep-sea environments that are otherwise inaccessible to humans.

Core Technologies of Underwater Robotics

Underwater robotics is a multidisciplinary field integrating mechanical engineering, computer science, electronics, and oceanography. These robots are engineered to operate in extreme underwater environments, relying on several key technical components and systems to function effectively.

Hull Design and Materials

The hull of an underwater robot must be able to withstand the immense pressure of deep-sea environments, where pressures can exceed 100 MPa (megapascals). Most underwater robots use materials like titanium or aluminum alloys for the main frame, as these materials offer excellent strength-to-weight ratios and resist corrosion in saline water.

Buoyancy management is equally critical. Syntactic foam, composed of hollow glass microspheres embedded in an epoxy resin matrix, is commonly used to maintain neutral buoyancy, minimizing energy expenditure during movement. The hull's hydrodynamic design also reduces drag, allowing the robot to move efficiently through dense water environments while conserving energy.1

Propulsion Systems

Underwater robots use thrusters and propellers optimized for thrust in water, which is more viscous than air. Multiple thrusters are typically employed to enable six degrees of freedom (DOF) movement: forward/backward, left/right, up/down, as well as rotational movements (pitch, yaw, and roll).

Modern AUVs feature energy-efficient thrusters that allow for extended operational periods. For deep-sea missions, low-noise electric thrusters are often preferred to minimize acoustic interference with sonar systems. Proper placement of these thrusters is vital for maintaining balance and stability during complex maneuvers in unpredictable underwater currents.1

Navigation and Control

Unlike surface or aerial robots, underwater robots cannot rely on global positioning system (GPS) signals due to signal attenuation in water. Instead, they employ a combination of Inertial Navigation Systems (INS), Doppler Velocity Logs (DVL), and acoustic positioning systems to determine their location. INS systems use accelerometers and gyroscopes to estimate changes in the robot’s position.1,2

DVL systems, on the other hand, measure velocity relative to the seabed, providing more accurate short-term location tracking. For long-distance missions, underwater robots often rely on acoustic positioning systems like ultra-short baseline (USBL) or long baseline (LBL) systems, where fixed transponders on the seabed provide location references. Control systems utilize advanced algorithms for real-time path planning, obstacle avoidance, and autonomous decision-making, critical in dynamic and cluttered underwater environments.1,2

Power Supply and Energy Management

Energy constraints significantly limit the operational range of underwater robots, especially AUVs, which rely on onboard power. Lithium-ion batteries are commonly used due to their high energy density and relatively lightweight design. However, the demand for longer missions has spurred research into alternative energy sources, such as fuel cells or ocean thermal gradient energy harvesting.

Robots operating at great depths optimize energy consumption by using low-power sensors and efficient thrusters. A growing trend is the deployment of underwater docking stations, allowing AUVs to recharge mid-mission. This innovation enables continuous operations without human intervention, extending both mission duration and depth.1

Sensors and Data Acquisition

Underwater robots use a variety of sensors for navigation, data collection, and task execution. Sonar systems, such as multi-beam and side-scan sonar, are essential for underwater mapping and obstacle detection, emitting acoustic pulses and measuring their reflections to generate 3D maps.

Optical sensors, including cameras and laser scanners, are used for close-range inspection tasks, although their performance decreases with turbidity and depth. Environmental sensors measure parameters like temperature, salinity, pressure, and turbidity, providing essential data for marine research. These robots also require robust real-time data acquisition systems to handle the large volumes of data they generate, transmitted via acoustic communication or stored for later analysis.1,3