Underwater surveillance has traditionally been carried out by means of surface and undersea manned vessels equipped with advanced sensor systems. This approach is often costly and manpower intensive. Marine robotics is an emerging technological area that enables the development of advanced networks for underwater surveillance applications. In contrast with the use of standard assets, these advanced networks are typically composed of small, low-power, and possibly mobile robots, which have limited endurance, processing and wireless communication capabilities. When deployed in a region of interest, these robots can cooperatively form an intelligent network achieving high performance with significant features of scalability, adaptability, robustness, persistence and reliability. Such networks of robots can be the enabling technology for a wide range of applications in the maritime domain. However, they also introduce new challenges for underwater distributed sensing, data processing and analysis, autonomy and communications. The main thrust of this study is to review the underwater surveillance scenario within a framework of four research areas: (i) underwater robotics, (ii) acoustic signal processing, (iii) tracking and distributed information fusion, and (iv) underwater communications networks. Progress in each of these areas as well as future challenges is presented.

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The interest in underwater communication has grown rapidly in the last few decades, as the ability to deploy assets at sea with increased levels of autonomy naturally led to the problem of getting data to and from them. Despite it's mature research topic status, underwater acoustic communications still faces high barriers when it comes to reaching consensus, not only on the communication processes but also on modelling and validation methodologies under which to perform objective comparison of methodologies. Having access to a persistent unattended infrastructure that enables long term testing of physical and logical underwater communications processes allows researchers to have access to precious real world data without the full cost of a sea trial and with the added bonus of potentially being able to capture variability on the seasonal scale. This paper presents the 2014 version of the Littoral Ocean Observatory Network (LOON): a test bed implemented by the NATO STO Centre for Maritime Research and Experimentation (CMRE), envisioned to foster cooperative development of underwater communications and networking. The data collection infrastructure provides a comprehensive data set of environmental, acoustic and packet measurements relevant to study the the communication processes for the physical and logical layers. This document focuses on the description of the test bed in its 2014 version, the expected benefits and the opportunities for the underwater communications research community.

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