There is no escaping fact that a huge amount of unexploited resources lies underwater which covers almost 70% of the Earth. Yet, the aquatic world has mainly been unaffected by the recent advances in the area of wireless sensor networks (WSNs) and their pervasive penetration in modern day research and industrial development. The current pace of research in the area of underwater sensor networks (UWSNs) is slow due to the difficulties arising in transferring the state-of-the-art WSNs to their underwater equivalent. Maximum underwater deployments rely on acoustics for enabling communication combined with special sensors having the capacity to take on harsh environment of the oceans. However, sensing and subsequent transmission tend to vary as per different subsea environments; for example, deep sea exploration requires altogether a different approach for communication as compared to shallow water communication. This paper particularly focuses on comprehensively gathering most recent developments in UWSN applications and their deployments. We have classified the underwater applications into five main classes, namely, monitoring, disaster, military, navigation, and sports, to cover the large spectrum of UWSN. The applications are further divided into relevant subclasses. We have also shown the challenges and opportunities faced by recent deployments of UWSN.

Underwater Wireless Sensor Network (UWSN) communication at high frequencies is extremely challenging. The intricacies presented by the underwater environment are far more compared to the terrestrial environment. The prime reason for such intricacies are the physical characteristics of the underwater environment that have a big impact on electromagnetic (EM) signals. Acoustics signals are by far the most preferred choice for underwater wireless communication. Because high frequency signals have the luxury of large bandwidth (BW) at shorter distances, high frequency EM signals cannot penetrate and propagate deep in underwater environments. The EM properties of water tend to resist their propagation and cause severe attenuation. Accordingly, there are two questions that need to be addressed for underwater environment, first what happens when high frequency EM signals operating at 2.4 GHz are used for communication, and second which factors affect the most to high frequency EM signals. To answer these questions, we present real-time experiments conducted at 2.4 GHz in terrestrial and underwater (fresh water) environments. The obtained results helped in studying the physical characteristics (i.e., EM properties, propagation and absorption loss) of underwater environments. It is observed that high frequency EM signals can propagate in fresh water at a shallow depth only and can be considered for a specific class of applications such as water sports. Furthermore, path loss, velocity of propagation, absorption loss and the rate of signal loss in different underwater environments are also calculated and presented in order to understand why EM signals cannot propagate in sea water and oceanic water environments. An optimal solk6ution for underwater communication in terms of coverage distance, bandwidth and nature of communication is presented, along with possible underwater applications of UWSNs at 2.4 GHz.

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Terrestrial and airborne Wireless Sensor Networks rely on radio frequencies as their communication medium for transmitting data and information. However, sensing and subsequent transmission in sub-sea environment e.g. deep sea exploration requires all together a different approach for communication that has to be done under water. There's no escaping the fact that a huge amount of unexploited resources lies in the 70% of the earth covered by oceans. Yet, the aquatic world has mainly been unaffected by the recent advances in the area of Wireless Sensor Networks (WSNs) and their pervasive penetration in modern day research and industrial development. The current pace of research in the area of Underwater Acoustic Sensor Networks (UASNs) is at a snail's pace due to the difficulties arising in transferring most of the land and air based WSNs' state-of-the-art to their underwater equivalent. Maximum underwater deployments rely on acoustics for enabling communication combined with special sensors having the capacity to take on harsh environment of the oceans. This paper particularly focuses on gathering most recent developments and experimentation related to key underwater sensor network applications and UASNs deployments for monitoring and control of underwater domains.

Abstract. Wireless Sensor Networks (WSNs) are increasingly being proposed in scenarios whose requirements cannot be fully predicted, or where the system functionality must adapt to changing conditions. In these scenarios, the ability to reconfigure portions of the software running on WSN nodes becomes imperative. At the same time, recent WSN proposals often employ heterogeneous nodes (e.g., sensors and actuators), which require the deployment of different code on different devices, based on their characteristics. Unfortunately, existing work in the field largely focuses on simpler scenarios where the same, monolithic program is distributed to all the nodes in the WSN. In this paper we present FIGARO, a programming model supported by an efficient run-time system and distributed protocols, collectively enabling an unprecedented fine-grained control over what is being reconfigured, and where. Using FIGARO, the programmer can deal explicitly with component dependencies and version constraints, as well as select precisely the subset of nodes targeted by reconfiguration, leaving the others unaltered. We show that our run-time support imposes a very limited processing and memory overhead, while the communication overhead lies within 9% of the theoretical optimum.