The autonomous underwater helicopter, shortly referred to as AUH, is a newly developed underwater platform with a unique disc shape. An autonomous underwater helicopter with a suboptimal disc shape is presented in this paper. It adopts a multirotor configuration and stable fins to overcome the shape shortcoming for motion stabilization. Its motion analysis and mathematical model have been introduced accordingly. Computational Fluid Dynamics (CFD) simulation is carried out to evaluate fins’ hydrodynamic performance. Proportional integral derivative (PID) and sliding mode fuzzy (SMF) control are adopted for controller design. Finally, the controller is applied on this AUH and extensively tested in various simulations and experiments, and the results illustrate the high stabilization and robustness of the controller and the hovering stability and manoeuvrability of AUH.

Accurate and reliable navigation is the prerequisite for autonomous underwater vehicles (AUVs) to perform tasks and ensure their safety. Conventional underwater navigation solutions are bulky, expensive, and power-hungry, increasing the AUV size and cost, which stifles the democratization of AUVs, especially for the trend of AUV miniaturization and swarm applications. This article presents a low-cost, power-efficient, and deployable approach to the navigation of micro AUVs. The approach, considered one-way travel-time hybrid baseline (OWTT-HBL) navigation, acoustically consists of two acoustic beacons forming a short baseline (SBL) and a passive inverted ultra-SBL (piUSBL) receiving array on the AUV. Signal broadcasting and acquisition are simultaneously triggered by onboard synchronized clocks for OWTT messaging. The AUV-mounted piUSBL receiving array determines the slant ranges and directions to the SBL beacons through matched filtering and array beamforming. An extended Kalman filter (EKF) state estimator is derived to fuse the acoustic range-angle measurements and the heading angular rate from a microelectromechanical system inertial measurement unit, providing the AUV coordinates and heading angles. A series of field experiments with a micro AUV were compared against the differential-GPS-recorded ground truth and a long baseline system, demonstrating the navigation capabilities. Field results show that the reported OWTT-HBL possesses an accuracy comparable to existing methods while showcasing the great potential for micro AUV navigation and multi-AUV systems.

Array calibration can effectively ensure the positioning accuracy of the ultra-short baseline (USBL) system. Traditional USBL array calibration methods focus on measuring the geometric position of the array elements. However, directional phase differences on the receive path are often ignored in the current calibration process, which can also cause array mismatch, especially when using the superdirective beamforming (SDB) technique. To further improve the calibration accuracy and convenience of the USBL using the SDB technique, a fast calibration method is proposed in this paper. In the new method, the hydrophone geometry error and the receiver path phase error are jointly considered. Then, two calibration models with different complexity are presented, and the conventional beamforming (CBF) beam output is deconvoluted with the calibrated beam pattern. The results of anechoic tank experiments show that the bearing root mean square error (RMSE) can be reduced from 1.663° to 0.081°, and the calibration time can be reduced from hours to tens of minutes.