Due to the power and transmission rate limitations, it is challenging to achieve underwater acoustic (UWA) communications over long distances from the unmanned underwater vehicle (UUV) to the shore station. As an alternative solution, the distributed acoustic sensing (DAS) underwater communication uses submarine optical cable to acquire and demodulate acoustic communication signals. There is little research on the channel and noise of DAS underwater communication. This paper analyzes the channel characteristics and the background noise of a DAS underwater communication system with armored optical cable based on the experimental measurements. Channel analysis shows that the envelope amplitudes of impulse responses follow the Burr distribution. The amplitudes get increased concentration at lower values as the sound source goes closer to the position right above the optical cable. Moreover, we observe that the received signals are influenced by the adjacent segments, leading to multiple arrivals within each acoustic bounce. Noise analysis shows that for frequencies lower than 1 kHz, unlike the Wenz noise spectrum primarily caused by shipping and wind, the −18 dB/octave decrease in power spectral density (PSD) of DAS noise is mainly caused by the equipment and cable themselves. The noise also exhibits full-band fluctuations. In underwater communications, full-band noise poses significant challenges for signal design. As far as we know, this article is the first report on the field experiment using a DAS underwater communication system equipped with armored optical cable, providing a reference for future underwater applications.

Underwater target detection is a pivotal technology in marine observation. Traditional detection methods primarily rely on acoustic and optical techniques. However, their accuracy is constrained in turbid waters and complex environments. Inspired by weakly electric fish, we present a spatially sensitive detection system based on active electrosense, capable of autonomously generating electric fields to identify underwater targets. This system incorporates the concept of multi-measurement vectors (MMVs) from compressed sensing and the direction of arrival estimation problem, adapting it to our specific application by utilizing spatial geometric information for multi-electrode signal detection. This approach effectively enhances detection sensitivity in both short distance and turbid water environments. Experiments in a saltwater pool demonstrated the system’s excellent current sensitivity to metallic targets, such as submarine cables, particularly at short distances. This capability addresses inherent challenges in traditional optical and acoustic methods, highlighting the practicality and effectiveness of the proposed system.

Underwater acoustic communication networks face unique challenges such as limited bandwidth, long propagation delay, and high error rate. To address these challenges, we propose a source-based disjoint multi-path routing protocol specifically designed for underwater acoustic networks. In this protocol, each data packet is routed based on the cost of relay nodes, which is determined by factors including initial hop count, energy consumption, and packet collision probability. Once the routing paths are established, the path costs are updated dynamically based on the costs of the relay nodes and their associated interference nodes. Simulation results demonstrate that the proposed routing protocol is able to enhance network throughput, reduce end-to-end delay, and increase packet delivery rate. Additionally, sea trials carried out in Zhoushan Archipelogoes, China, have confirmed that the proposed method can effectively reduce packet collisions by considering inter-path data transmission interference in high-load network scenarios. Compared with the single-path approach and non-weighted approach, this approach significantly reduces end-to-end delay and improves overall network throughput and packet delivery rate.

Submarine cables are widely laid all over the world. However, they are not completely fixed in practice and are subject to displacement by currents and typhoons. To maintain and repair the submarine cables, it is necessary to detect their positions. Using a remotely operated vehicle (ROV) equipped with magnetometers is a common way for submarine detection. However, as ROVs develop toward electrification and large scale, the interference of electric drives on the magnetometer is significant. Magnetic interference and noise in the environment affect the signals of magnetometers, reducing the accuracy of submarine cable detection. In this paper, a two-step method is proposed to reduce the influence of magnetic noise and interference. In the first step, we eliminate magnetic interference based on its correlation with motor speed. In the second step, wavelet transform is used to eliminate environmental magnetic noise. According to the simulation and on-site test, this method can reduce the magnetic interference caused by brushless DC motors and improve the accuracy of magnetic detection and positioning of submarine cables.

Direct acoustic communication between underwater and airborne nodes has always been considered unfeasible due to the energy loss caused by the strong surface reflection of sound waves. However, contrary to popular belief, our study demonstrates that underwater transducers can effectively transmit detectable acoustic signals in the air. To investigate this phenomenon, we conducted an experiment involving the deployment of an underwater transducer at a depth of 1 m, while an unoccupied aerial vehicle equipped with a voice recorder was positioned at various altitudes ranging from 2 to 30 m and horizontal distances of 0–30 m. Sound pressure levels were measured at 20 different positions within the frequency range of 10–20kHz, and orthogonal frequency division multiplex acoustic communication signals were recorded at specific positions. Our findings reveal the successful establishment of a direct acoustic communication link between the water and air interface, achieving a data rate of 4.565 kbps. This study opens up new possibilities for practical applications in underwater-to-air communication systems.

With the rapid advancement of underwater communication and unmanned aerial vehicle (UAV) technologies, the potential applications of cross-medium communication in environmental monitoring, maritime Internet of Things (IoTs), and rescue operations, in particular, have attracted great attention. This study explores the feasibility of achieving cross-medium direct acoustic communication through the air–water interface. Specifically, it investigates challenges such as acoustic impedance mismatches and signal attenuation caused by energy loss during interface transmission, aiming to understand their impact on communication performance. Experimental tests employed underwater acoustic transducers as signal transmitters to propagate sound waves directly into the air, attempting to establish communication links with aerial UAV nodes. Preliminary experimental results indicate that even conventional underwater acoustic transducers can achieve information exchange between underwater nodes and UAVs, laying a foundation for further research and application of cross-medium communication systems.