Differential Pressure Sensor Speedometer for Autonomous Underwater Vehicle Velocity Estimation

Velocity estimation is central for the reliable navigation of autonomous underwater vehicles (AUVs). Doppler velocity logs (DVLs), currently the leading technology for underwater velocity estimation, can be too big, expensive, and energy consuming to be used on low-cost and small AUVs or for long missions. In our previous work, a system based on differential pressure sensors was developed for estimating surge velocity. In this paper, we combine this system with an inertial measurement unit to compensate for orientation errors and create a differential pressure sensor speedometer (DPSS). We propose and demonstrate the DPSS prototype as an important step toward a small, inexpensive, and energy-efficient alternative or complement to a DVL in certain applications. This paper presents the first underwater field tests of a sensor using differential pressure for velocity estimation. Tests were conducted with a SPARUS II AUV (IQUA Robotics, Girona, Spain). To demonstrate the efficacy of our proposed solution, we compare the surge velocity estimation of the DPSS and the vehicle's DVL in bottom and water locks. Trials were conducted by varying the trajectory and velocity of the vehicle in three different environments. We show that the DPSS displayed a superior performance with respect to the DVL water lock for velocities above 0.6 m/s. The differences in the velocity estimations of the DVL in bottom lock for high velocities were as small as 0.013 m/s. These results encourage further development of the presented technology.