In this paper we present a novel platform for underwater sensor networks to be used for long-term monitoring of coral reefs and fisheries. The sensor network consists of static and mobile underwater sensor nodes. The nodes communicate point-to-point using a novel high-speed optical communication system integrated into the TinyOS stack, and they broadcast using an acoustic protocol integrated in the TinyOS stack. The nodes have a variety of sensing capabilities, including cameras, water temperature, and pressure. The mobile nodes can locate and hover above the static nodes for data muling, and they can perform network maintenance functions such as deployment, relocation, and recovery. In this paper we describe the hardware and software architecture of this underwater sensor network. We then describe the optical and acoustic networking protocols and present experimental networking and data collected in a pool, in rivers, and in the ocean. Finally, we describe our experiments with mobility for data muling in this network.

A number of multi-hop, wireless, network programming systems have emerged for sensor network retasking but none of these systems support a cryptographically-strong, publickey-based system for source authentication and integrity verification. The traditional technique for authenticating a program binary, namely a digital signature of the program hash, is poorly suited to resource-contrained sensor nodes. Our solution to the secure programming problem leverages authenticated streams, is consistent with the limited resources of a typical sensor node, and can be used to secure existing network programming systems. Under our scheme, a program binary consists of several code and data segments that are mapped to a series of messages for transmission over the network. An advertisement, consisting of the program name, version number, and a hash of the very first message, is digitally signed and transmitted first. The advertisement authenticates the first message, which in turn contains a hash of the second message. Similarly, the second message contains a hash of the third message, and so on, binding each message to the one logically preceding it in the series through the hash chain. We augmented the Deluge network programming system with our protocol and evaluated the resulting system performance.

This report summarizes our research directions in underwater sensor networks. We highlight potential applications to off-shore oilfields for seismic monitoring, equipment monitoring, and underwater robotics. We identify research directions in short-range acoustic communications, MAC, time synchronization, and localization protocols for highlatency acoustic networks, long-duration network sleeping, and application-level data scheduling. 1

Abstract — We propose a novel modular underwater robot which can self-reconfigure by stacking and unstacking its component modules. Applications for this robot include underwater monitoring, exploration, and surveillance. Our current prototype is a single module which contains several subsystems that later will be segregated into different modules. This robot functions as a testbed for the subsystems which are needed in the modular implementation. We describe the module design and discuss the propulsion, docking, and optical ranging subsystems in detail. Experimental results demonstrate depth control, linear motion, target module detection, and docking capabilities. Index Terms — Modular robot, underwater robot, selfreconfiguring robot, optical ranging.

While self-deployment/reconfiguration of terrestrial wireless sensor networks (WSNs) has been studied extensively, such selforganization has just started to receive attention for Underwater Acoustic Sensor Networks (UWSNs). Particularly, self-deployment of sensor nodes in UWSNs is challenging due to certain characteristics of UWSNs such as three dimensional (3-D) environment, restrictions on node movement and longer delays in communication. Given these characteristics, self-deployment of sensor nodes should not only ensure the necessary coverage but also guarantee the connectivity for data transmission as in the case of terrestrial WSNs. In this paper, we propose a distributed node deployment scheme which can increase the initial network coverage in an iterative basis. Assuming that the nodes are initially deployed at the bottom of the water and can only move in vertical direction in 3-D space, the idea is to relocate the nodes at different depths based on a local agreement in order to reduce the sensing overlaps among the neighboring nodes. The nodes continue to adjust their depths until there is no room for improving their coverage. We tune the parameters of the algorithm to also provide connectivity of the network with a surface station. We compared the coverage and connectivity performance of this distributed scheme with distributed/semi-distributed baseline schemes and centralized schemes which can provide optimal coverage/connectivity. We also provide several observations regarding the coverage/connectivity performance and message/travel/time complexity of the proposed approach. Key words: UWSNs; underwater sensor deployment; self-organization; 3-D coverage; underwater mobility 1.

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selves at a safe distance, from which they can control the fire without being damaged. Finally, the node density We consider the problem of self-deployment and re- should be increased in proximity of the fire front so as to location in mobile wireless networks, where nodes are contain its expansion. both sensors and actuators. We propose a unified, dis- In this work, we present a distributed solution that is tributed algorithm that has the following features. Dur- able to meet all of the above requirements. Our network ing deployment, our algorithm yields a regular tessella- system is composed of numerous mobile sensor-actuator tion of the geographical area with a given node density, nodes that autonomously organize and react to triggers called monitoring configuration. Upon the occurrence of from the environment. The specific problem we address a physical phenomenon, network nodes relocate them- here is how to enable these nodes to both self-deploy and selves so as to properly sample and control the event, relocate in a distributedfashion. while maintaining the network connectivity. Then, as Traditionally, network deployment [6] is performed soon as the event ends, all nodes return to the monitoring at the initial stage of the network functioning, to obtain configuration. To achieve these goals, we use a virtual the desired geographical coverage or spatial sensor denforce-based strategy, which proves to be very effective sity. For the particular applications that we consider, selfeven when compared to an optimal centralized solution. deployment of mobile sensor-actuators is necessary since node placement cannot be performed manually and accu-

In this paper we describe cooperative control algorithms for robots and sensor nodes in an underwater environment. Cooperative navigation is defined as the ability of a coupled system of autonomous robots to pool their resources to achieve long-distance navigation and a larger controllability space. Other types of useful cooperation in underwater environments include: exchange of information such as data download and retasking; cooperative localization and tracking; and physical connection (docking) for tasks such as deployment of underwater sensor networks, collection of nodes, and rescue of damaged robots. We present experimental results obtained with an underwater system that consists of two very different robots and a number of sensor network modules. We present the hardware and software architecture of this underwater system. We then describe various interactions between the robots and sensor nodes and between the two robots, including cooperative navigation. Finally, we describe our experiments with this underwater system and present data. 1