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Remotely-Operated Vehicle applications in port and harbor site characterization: Payloads, platforms, sensors, and operations

Remotely-Operated Vehicles (ROVs) serve many functions during site characterization surveys including dive team assistance, quality control, and anomaly reacquisition. Reacquisition applications require detection, geo-registration, and investigation of items of interest located on, or below, the seafloor. Underwater target detection using ROVs poses many challenges. Detection sensors must be mounted far enough away from the vehicle to reduce noise effects from thrusters and other vehicle sensors. Conversely, detection sensors must be mounted close enough to the vehicle to maintain vehicle maneuverability. Vehicle noise characterization with respect to sensor standoff and orientation is discussed. ROV applications require the collection of correlated detection sensor data along with global position information. Positional accuracy varies depending on the method used and can be dependent on site and deployment conditions. Positioning systems, including Ultra-Short Base Line (USBL), Doppler Velocity Logs (DVL), and Real-time Kinematic Global Positioning System (RTK-GPS) are discussed with respect to underwater object localization. We present the development of underwater metal detection systems consisting of magnetometer and electromagnetic induction (EMI) sensors mounted on a mini-ROV. Detection sensors include fluxgate magnetometers and a diver handheld EMI sensor modified for data transmission through the ROV umbilical for digital data capture and audio data delivery topside. Sensor sensitivities are defined through analysis of data collected against targets of various sizes. We discuss the development, performance, and operation of various payloads for different applications and compare ROV and dive team results and efficiency.