Underwater gliders travel through the ocean by buoyancy control, which makes their motion silent and involves low energy consumption. Due to those advantages, numerous studies on underwater acoustics have been carried out using gliders and different acoustic payloads have been developed. This paper aims to illustrate the use of gliders in underwater acoustic observation and target detection through experimental data from two sea trials. Firstly, the self-noise of the glider is analyzed to illustrate its feasibility as an underwater acoustic sensing platform. Then, the ambient noises collected by the glider from different depths are presented. By estimating the transmission loss, the signal receiving ability of the glider is assessed, and a simulation of target detection probability is performed to show the advantages of the glider over other underwater vehicles. Moreover, an adaptive line enhancement is presented to further reduce the influence of self-noise. Meanwhile, two hydrophones are mounted at both ends of the glider to form a simple array with a large aperture and low energy consumption. Thus, the target azimuth estimation is verified using broadband signals, and a simple scheme to distinguish the true angle from the port‒starboard ambiguity is presented. The results indicate that the glider does have advantages in long-term and large-scale underwater passive sensing.

Underwater gliders are widely used in ocean observation with long operational endurance. Since gliders use buoyancy to generate gliding motion through water columns with a pair of wings, they are susceptible to ocean currents. With the limited navigation capability, the position deviation is usually quite large. To improve the localization accuracy of the glider, a passive acoustic method is proposed, in which a sound source periodically sends signals and two hydrophones mounted on the glider are employed to receive signals. The extended Kalman filter is developed to estimate the positions of gliders and the depth-dependent currents using the time difference of arrival between the signal receptions and the direction of signal arrival. Both the hydrophones and the source are assumed as nonsynchronous, and to obtain the direction of arrival, an algorithm using the self-noise to synchronize two hydrophones mounted on the glider is proposed. Simulations with different scenarios are carried out and data from a field experiment performed at the South China Sea are processed to demonstrate the method.