The role of acoustics in underwater robotics
Radio signals hardly propagate underwater, therefore radio-frequency based solutions that are routinely used above water (like GPS and other GNSS) are virtually useless in the underwater domain. On the other hand, sound waves propagate better in water than they do in air, therefore acoustics has been a major source of solutions to help solving the underwater localization challenges. In the domain of underwater robotics, the main task of the onboard navigation system is to estimate its own position and attitude in real time. This serves for the control system to make necessary corrections in trajectory, and, at the same time, it allows sensor data to be spatially tagged. A typical navigation system fuses together data from multiple sensors, like pressure sensors, digital compasses, IMUs, accelerometers, gyroscopes, and Doppler velocity meters. Even with the best of specs, these data alone produce position estimates with errors that grow in time due to continuous integration of biases. The use of acoustic signals to provide range and bearing to specific locations can provide absolute measurements and avoid divergence. The Center for Robotics and Autonomous System of INESC TEC in Porto, Portugal, has been involved in many R&D projects developing cutting-edge technology for the underwater environment. One example of specialization is underwater navigation, a topic of active research for more than 20 years. This lecture will address some of the flagship projects of the Center in underwater robotics, with an emphasis on acoustic based devices and algorithms developed to maximize their usefulness in marine scenarios.