Theofanis P. Lambrou

A Low-Cost Sensor Network for Real-Time Monitoring and Contamination Detection in Drinking Water Distribution Systems

This paper presents a low cost and holistic approach to the water quality monitoring problem for drinking water distribution systems as well as for consumer sites. Our approach is based on the development of low cost sensor nodes for real time and in-pipe monitoring and assessment of water quality on the fly. The main sensor node consists of several in-pipe electrochemical and optical sensors and emphasis is given on low cost, lightweight implementation, and reliable long time operation. Such implementation is suitable for large scale deployments enabling a sensor network approach for providing spatiotemporally rich data to water consumers, water companies, and authorities. Extensive literature and market research are performed to identify low cost sensors that can reliably monitor several parameters, which can be used to infer the water quality. Based on selected parameters, a sensor array is developed along with several microsystems for analog signal conditioning, processing, logging, and remote presentation of data. Finally, algorithms for fusing online multisensor measurements at local level are developed to assess the water contamination risk. Experiments are performed to evaluate and validate these algorithms on intentional contamination events of various concentrations of escherichia coli bacteria and heavy metals (arsenic). Experimental results indicate that this inexpensive system is capable of detecting these high impact contaminants at fairly low concentrations. The results demonstrate that this system satisfies the online, in-pipe, low deployment-operation cost, and good detection accuracy criteria of an ideal early warning system.

A Survey on Routing Techniques Supporting Mobility in Sensor Networks

Wireless sensor networks (WSNs) consist of small nodes with sensing, computation, and wireless communications capabilities. Even in predominantly static sensor networks, it is possible to have a few mobile nodes. Mobility of nodes in WSNs adds a significant challenge. In this article we present a survey of state-of-the-art routing techniques in wireless ad hoc and sensor networks and highlight the advantages/disadvantages and performance issues of each routing technique. The aim is to identify routing protocols that will be able to support the mobility of sensor nodes in WSNs consisting of both static and mobile (mixed WSN) nodes. The article concludes by presenting an approach for such a routing protocol.

A Nephelometric Turbidity System for Monitoring Residential Drinking Water Quality

In this paper the design and development of a turbidity system for monitoring drinking water quality in households is presented. Its operation is based on the principle that the intensity of the light scattered by the suspended matter is proportional to its concentration. Unlike the commercially available turbidity meters, which are relatively expensive and bulky, the proposed device is small-sized, low power, lightweight, easy to use and inexpensive. Laboratory tests of the device have yielded satisfactory repeatability and precision. This sensor can be used as a part of a low cost sensor network consisting of different types of sensors (pH, temperature, chloride, etc) to provide water quality information to consumers. Fusing on-line multi sensor measurements, the system can provide useful information regarding hazardous agents and waterborne pathogens contaminants of household drinking water raising awareness and encourage better water-handling.

A low-cost system for real time monitoring and assessment of potable water quality at consumer sites

This paper presents the design and development of a low cost system for real time monitoring of drinking water quality at consumer sites. The system consists of several in-pipe electrochemical and optical sensors and emphasis is given on low cost, lightweight implementation and reliable long time operation. Such implementation is suitable for large deployments enabling a sensor network approach for providing spatiotemporally rich data to water consumers, water companies and authorities. Extensive literature and market research is performed to identify low cost, on-line sensors that can reliably monitor several parameters which can be used to infer the water quality. Based on selected parameters a sensor array is developed along with several microsystems for analog signal conditioning, processing, logging, and remote presentation of data. Finally, an algorithm for fusing on-line multi sensor measurements is developed to assess the water contamination risk.

Collaborative event detection using mobile and stationary nodes in sensor networks

Monitoring a large area with stationary sensor networks requires a very large number of nodes which with current technology implies a prohibitive cost. The motivation of this work is to develop an architecture where a set of mobile sensors will collaborate with the stationary sensors in order to reliably detect and locate an event. The main idea of this collaborative architecture is that the mobile sensors should sample the areas that are least covered (monitored) by the stationary sensors. Furthermore, when stationary sensors have a ldquosuspicionrdquo that an event may have occurred, they report it to a mobile sensor that can move closer to the suspected area and can confirm whether the event has occurred or not. An important component of the proposed architecture is that the mobile nodes autonomously decide their path based only on local information (their own beliefs and measurements as well as information collected from the stationary sensors in their communication range). We believe that this approach is appropriate in the context of wireless sensor networks since it is not feasible to have an accurate global view of the state of the environment.

Collaborative path planning for event search and exploration in mixed sensor networks

Mixed Wireless Sensor Network (WSN) is a network that consists of static and mobile sensor nodes. This article presents a collaborative framework where a team of autonomous mobile sensor nodes navigate through a sparse network with static sensors to improve the overall area coverage and search for events that may have occurred in areas not monitored by the static network. The mobile sensor nodes have limited communication and sensing ranges and collaborate to autonomously and dynamically decide their trajectories to enhance the area coverage, avoiding obstacles and collisions and adapting to new information such as failures of static nodes. In the context of the proposed framework, one can address various trade-offs. Examples include the trade off between the area coverage and the energy cost in terms of traveled distance and the one between the area coverage and information exchange among the mobile nodes. Furthermore, the proposed framework can be used to address spatially adaptive sampling. Finally, the proposed framework has been evaluated under different scenarios and has been shown to perform very well.

A testbed for coverage control using mixed wireless sensor networks

Wireless sensor networks (WSNs) is a relatively new technology that has been proposed for several applications including wide area monitoring. Such applications may include stationary or mobile sensor platforms or they may include several stationary and some mobile-robotic sensor nodes that can move in the area in order to achieve certain objectives, e.g., monitor areas that are not adequately covered or assist in the transfer of data to prevent the energy depletion of certain critical nodes. Such networks that consist of both stationary and mobile nodes are referred to as mixed WSNs. This paper presents the development of an experimental testbed for mixed WSNs consisting of stationary and mobile sensor nodes that collaborate to improve the sensing coverage and event detection of the network in a given deployment area. The paper describes the hardware and infrastructure of the testbed as well as a case study for coverage control that was investigated using the testbed. We point out that the developed testbed can be used for the evaluation and validation of different algorithms for coverage control that involve collaboration between stationary and mobile sensors to improve the WSNs monitoring capabilities. In addition, it can also be used to investigate other objectives as well as other concepts (e.g., network control).

Distributed collaborative path planning in sensor networks with multiple mobile sensor nodes

This paper presents an efficient distributed collaboration scheme for a team of autonomous mobile sensor nodes which enables them to navigate through a sparse sensor network with stationary nodes searching for events and improving area coverage. The mobile sensor nodes have limited communication and sensing ranges and autonomously plan their trajectories in order to enhance the probability of event detection. The main objective of this work is to investigate collaboration schemes between the sensor nodes such that each mobile samples areas not covered by the stationary or other mobile nodes. The aim is to reduce the amount of information that needs to be exchanged between nodes without significant loss of performance (in terms of area coverage).

Optimized Cooperative Dynamic Coverage in Mixed Sensor Networks

This article considers the problem of improving the dynamic coverage and event detection time of mixed wireless sensor networks (WSNs). We consider mixed WSNs that consist of sparse static sensor deployments and mobile sensors that move continuously to monitor uncovered (vacant) areas in the sensor field. Mobile sensors move autonomously and cooperatively by executing a path planning algorithm. Using a simplified scenario, the article derives the optimal path strategy for a single mobile sensor to search two nonconnected uncovered regions with the minimum average detection delay or with the maximum dynamic coverage. The resulting optimal strategy confirms that it is better to search areas that are less likely to hide a target but are located closer to the mobile node, rather than heading toward the most likely area. Based on the insights gained from the simplified scenario and the theory of coverage processes, the article proposes a surrogate method to approximate the best searching neighborhood radius (a design parameter of the path planning algorithm) that optimizes the dynamic coverage and event detection time capabilities of mixed WSN deployments. Extensive simulation results indicate that this approach can achieve very good results, both for a single and for multiple collaborating mobile sensors.

On the optimal search neighborhood in Mixed Wireless Sensor Networks

This paper considers the problem of improving the monitoring capability of a sparse stationary sensor network with mobile sensor nodes. The main idea is that the mobile sensors should sample the areas that are least covered (monitored) by the static sensors. Thus, a simple path planning strategy is presented that decides the next point to be visited using only “local” information. For a simplified scenario, the paper derives the optimal path strategy and extrapolates some of the properties of the scenario to a more general instance of the problem. Furthermore, the paper proposes a surrogate metric that can be used in order to determine the optimal searching neighborhood and presents extensive simulation results which indicated that this approach can achieve very good results.