Lake Monitoring Sensors Distribution with Low Energy Consumption Pudith Sirigrivatanawong, Shogo Arai, and Koichi Hashimoto Abstract— Lake monitoring sensors are important for main- taining the safe environment around the lake. Those sensors ﬂoat on a lake and have to carry their own battery. However, the limited battery life in sensors is a critical problem, because it affects the operation time of the system. In this paper, we address the lake monitoring sensors distribution under water ﬂow ﬁeld in a lake. We propose a controller that control the group distribution by using the centroid and the variance of the group as control parameters. The proposed controller considers the existing ﬂow ﬁeld and uses it in the calculation process. This action provides lower energy consumption by the help of the ﬂow ﬁeld. Results from the proposed controller is compared with the results from a simple distribution method, which is performed by controlling positions of the sensors and using a simple feedback control and compared with results from a modiﬁed consensus controller. With a distribution method that requires less energy, the sensors can reach their objective with sufﬁcient amount of energy that would allow a greater overall operating time of the monitoring system, which would in turn result in higher monitoring system efﬁciency. I. INTRODUCTION People have been involving with natural resources since the beginning of human life [1]. One of the most valuable natural resources that have inﬂuenced human life is water. Water resources are divided in to many categories such as river, lake, and ocean, according to the physical character- istics. In recent years, there are many studies on physical quantities of the water resources and many researches have been done on the measurement of the ﬂow ﬁeld of water in river, lake, and ocean, such as [2],[3],[4],[5],[6],[7]. This shows the increasing of interests of water resource moni- toring. This paper consider a measurement of water quality parameters using monitoring buoys or sensors nodes. The advantages of using the sensors node are the coverage area of monitoring and not only ﬂow ﬁeld that can be measured but also temperature, local weather condition, carbon ﬂux, and the behaviour of ﬁsh and invertebrates [8]. Besides other forms of water resources, this paper consider a monitoring system in lake. Lakes are highly valued for their biological diversity. They provide foods and habitats for many lives in them. Majority of the lakes are fresh water lake, which are one of the most valuable natural resources. Unfortunately, this valuable natural resource is getting polluted due to various human activities. In order to treat a polluted lake, the information such as temperature, water current, and chemical concentration are necessary. Therefore, the demand for water quality monitoring sys- tem or early water quality warning system is increasing All authors are with the Graduate School of Information Sci- ences, Tohoku University, Sendai, Japan. Emails: {pudith, arai, koichi}@ic.is.tohoku.ac.jp in order to provide a safer environment [9]. In order to perform the water quality monitoring system for a lake, it is necessary to deploy sensors nodes that can gather required information. Sensor node deployment via helicopter or boat is costly. In comparison, sensor nodes distribution method that have sensors distribute themselves have lower cost than the previously stated methods. Self distribution method has an advantage in terms of distribution cost, but it falls behind in term of energy consumption. Since sensors are required to spend their limited energy in propagating toward their designated destinations, the energy consumption caused by self distribution of the sensors can pose a critical problem in deploying a long lasting monitoring system. The energy consumption problem has been a problem for a lake monitoring sensor network. A robotic sensor network proposed in [10] uses small, lightweight robotic rafts to monitor common carp tagged with radio transmitters across Minnesota lakes. One of the main problem of this system is that each raft only has approximately 5 hours of battery life. The authors mentioned that this problem can be migrated by adding solar panel to the raft. However, since the data collection needs to be done during night and day, the solar panels alone is not suitable for solving this problem. Some works present a solution, which involved controlling a system with a group of agents. [11] addresses the problem of controlling a group of agents towards a consensus point. A leader-follower formation control of multiple autonomous mobile robots has been studied by [12]. [13] focuses on the control problem of multiagent systems under unknown and persistent disturbances. Although these papers have provided the control input results, but none of them lowers the amount of control input by using help of water ﬂow ﬁeld. Furthermore, the dynamics system in those papers are ﬁrst order dynamics system, which can not be used to describe the motion of lake monitoring sensor in a lake. The lake monitoring sensor movement involves with force and acceleration. Therefore, it needs second order dynamics system to describe the sensor movement. This paper considers controlling centroid and variance of a group of sensors and utilizing forces existing in such the lake to help the distribution. These forces are in forms of drag forces and they exist everywhere in the lake vary- ing in magnitude and direction. By utilizing these forces, the overall energy consumption can be reduced. Thus, the monitoring system operating time can be extended and the system efﬁciency will increase. Our proposed control method provides a way to use those forces to reduce the energy consumption of the distribution by taking the ﬂow ﬁeld in the lake into consideration while controlling the centroid and the 978-1-4799-2744-9/13/$31.00 ©2013 IEEE Proceeding of the IEEE International Conference on Robotics and Biomimetics (ROBIO) Shenzhen, China, December 2013 2062