Differential Pressure Sensors for Underwater Speedometry in Variable Velocity and Acceleration Conditions

Autonomous underwater vehicles require estimation of their velocity relative to the surrounding flow to perform essential navigation tasks. Available technologies for speed estimation rely on Doppler velocity logs or acoustic Doppler current profilers and are not suitable for application in small low cost or energy consumption vehicles. Encouraged by the successful results of our previous lab-scale investigations using pressure-based speedometry, we developed differential pressure sensor speedometry as an alternative to conventional technologies. We built a full-scale physical prototype, compared analog and digital differential pressure sensors and evaluated the performance in variable velocity (0-2 m/s) and acceleration (0-2 m
²
/s) conditions in a marine tow tank. A simple equation based on the conservation of energy accurately estimated the velocity, with estimated mean absolute errors of 0.0087 m/s for analog and 0.0107 m/s and digital configurations. This equation is shown to hold under variable velocity and acceleration conditions. We conclude that differential pressure sensor speedometry is a valid solution to perform underwater speedometry and we confirm that the system can provide instantaneous and stable velocity estimates with a sampling rate higher than 10 Hz.