UC San Diego

Research results that advance the capabilities of autonomous underwater vehicles (AUVs) to conduct seabed surveys are described. These include the creation of a software framework to enable research and development in sensing and adaptive autonomy, a novel synthetic baseline navigation technique, and a magnetic sensing system that incorporates sense and react behaviors. Field experiments were conducted globally in a wide range of littoral environments to test hypotheses associated with the emerging field of autonomy as applied to underwater systems.

To facilitate sensor integration and provide a testbed for autonomous sense and react research, an onboard sensor processing and autonomy system was developed for the REMUS AUV using the Robot Operating System (ROS) that provides high-level control of the vehicle. Multiple vehicles outfitted with this system were used for seabed surveys, sensor evaluation, and engineering tests. This framework enabled the development of novel techniques for undersea navigation and magnetic sensing.

A synthetic baseline navigation technique that self-localizes an AUV using intermittent acoustic communications signals received by a single transducer is presented. The methodology is found to offer advantages over traditional acoustic-based navigation, in that it can operate with or without synchronized clocks, does not require acoustic transmissions dedicated to navigation, and can provide faster navigation solution convergence. The method uses the phase measurement at the output of a second-order phase-locked loop (PLL) to create fine-scale pseudo-range estimates in addition to, or in the absence of, a one-way travel time (OWTT) measurement based on the arrival time of the acoustic data packet. These range measurements are incorporated by an adaptive particle filter. This technique allows the vehicle navigation system to take advantage of multiple phase-derived range measurements made over the duration of a communication packet.

To enable geophysical and archaeological survey capabilities, a scalar magnetometer system has been developed and integrated into an AUV. Real-time signal processing mitigates platform effects of the vehicle. Development of autonomy for on-board processing and target detection, coupled with reacquisition behaviors, is found to increase the effective survey coverage rate by nearly 300% when searching for magnetic dipole targets.

The compact system collects data from a Micro-Fabricated Atomic Magnetometer (MFAM, Geometrics Corporation, San Jose, CA, USA), a total-field atomic magnetometer, and data from the sensor is both streamed to storage and made available to an onboard autonomy engine for real-time sense and react behaviors. Following characterization both in controlled laboratory conditions and at sea to determine its performance limits, methodologies for processing the magnetometer data to correct for interference and error introduced by the AUV platform were developed to improve sensing performance. When conducting seabed surveys, the developed autonomy is found to reliably detect and characterize targets of interest using physics-based algorithms designed to operate in real-time within the computational constraints of the AUV. Over the course of this research, the system was advanced to drive both single- and multiple-vehicle autonomous target reacquisition behaviors. Detailed results from surveys searching for submerged World-War II aircraft wrecks at locations worldwide are presented.