Monitoring the underwater world is a challenging task due to its complexity, size and extreme harshness, as well as the limited technology we can count on today. Current monitoring solutions suffer from costly and difficult installations and sometimes dangerous operations. Once installed, collecting the data from the underwater sensing systems is by no means simple. Existing sensor networks in the radio frequency domain do not map very well to underwater networks. Cheaper and smaller hardware platforms are needed to allow the benefits such as multi-hop communication, mesh networking, and the resulting higher reliability compared to single point-to-point links used today. Existing networking protocols from radio frequency domain sensor networks also do not work well under water because of the harsh environmental conditions as well as long propagation delays, low bandwidth, and frequency dependent attenuation. Refraction of the acoustic signal also causes shadow zones, which pose problems to reliable communication.

At the same time, the need for underwater communication systems with high data rates over considerably longer distances for applications such as energy production (oil, gas extraction), energy distribution (e.g., oil plants, oil transport, seaport monitoring), and monitoring wellbeing of marine life has been significantly increased.

This special issue solicits original contributions, addressing challenges of underwater sensor networks. Papers describing innovative systems, solutions, and practical approaches or engineering contributions, which are extensively tested in simulation environments and/or real-world experimental settings are specially welcome.

Topics of interest include, but not limited to:
• New underwater sensing and communication platforms
• Acoustic signal propagation and physical layer including modulation and MIMO
• Underwater communication
• Underwater MAC and routing
• Underwater localization and time synchronization
• Distributed signal processing under water
• Collaborative underwater beam forming
• Distributed data processing and event detection under water
• Underwater power management
• Underwater change detection
• Test methods for Underwater Sensor Networks
• Autonomous adaptive mission planning and execution
• Coordination of underwater sensors networks and UAVs
• Underwater swarm robotics
• Autonomous underwater surveillance systems