Dear Colleagues,

Even though the oceans play a major role in the regulation of Earth's ecosystems, there is still a large fraction of the worlds' oceans that remain unexplored. One of the reasons is that saltwater virtually blocks electromagnetic propagation, which disallows the use of ubiquitous remote-sensing techniques available for sampling large continental areas. In most cases, underwater measurements must be performed in situ, demanding a proximity between the sensors and the region of interest and exposing the sensors to the dynamic and harsh nature of the underwater marine environment. These localized measurements also result in poor space-and-time sampling scales, which are often improved with the use of robotic systems. However, the integration of sensors in moving platforms may result in the degradation of data quality as a result of different sources of contamination (e.g., temperature influence, water mixing, water dragging, etc.). In this kind of application, the perception of the environment is affected by the quality of the sensor data, by tools that combine these measurements into computed water characteristics, and by sensors and methods that are used to determine the location of the platforms that are taking the measurements. This Special Issue addresses these multiple aspects related to the use of sensors for underwater perception. Recent years have shown innovative tools and methods to take accurate measurements of water properties, and to estimate characteristics of the underwater environment. At the same time, the increase in computational power has allowed for the implementation of complex algorithms in real time, ensuring unprecedent resolution in mapping, localization, and general perception of the environment. This Special Issue seeks innovative works in a wide range of research topics, spanning both theoretical and systems research, including results from industry and academic/industrial collaborations, related but not restricted to the following topics:

• Sensors for fundamental properties of seawater;
• Targeted sampling;
• Optical sensors;
• Acoustic sensors;
• New sampling tools and methods;
• Distributed perception;
• Cooperative perception;
• Algorithms to combine sensors for underwater navigation or localization;
• Design of underwater navigation or localization systems combining multiple sensors;
• Filtering techniques for multisensor fusion.

Dr. Nuno A. Cruz
Prof. Dr. Pedro Jorge
Guest Editors

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