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Silent localization of underwater sensors using magnetometers

Silent localization of underwater sensors using magnetometers

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Hindawi Publishing Corporation EURASIP Journal on Advances in Signal Processing Volume 2010, Article ID 709318, 8 pages doi:10.1155/2010/709318 Research Article Silent Localization of Underwater Sensors Using Magnetometers Jonas Callmer, Martin Skoglund, and Fredrik Gustafsson (EURASIP Member) Division of Automatic Control, Department of Electrical Engineering, Link¨oping University, 581 83 Link¨oping, Sweden Correspondence should be addressed to Jonas Callmer, [email protected] Received 1 July 2009; Accepted 15 October 2009 Academic Editor: Dirk Maiwald Copyright © 2010 Jonas Callmer et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Sensor localization is a central problem for sensor networks. If the sensor positions are uncertain, the target tracking ability of the sensor network is reduced. Sensor localization in underwater environments is traditionally addressed using acoustic range measurements involving known anchor or surface nodes. We explore the usage of triaxial magnetometers and a friendly vessel with known magnetic dipole to silently localize the sensors. The ferromagnetic field created by the dipole is measured by the magnetometers and is used to localize the sensors. The trajectory of the vessel and the sensor positions are estimated simultaneously using an Extended Kalman Filter (EKF). Simulations show that the sensors can be accurately positioned using magnetometers. 1. Introduction Today, surveillance of ports and other maritime envi- ronments is getting increasingly important for naval and customs services. Surface vessels are rather easy to detect and track, unlike submarines and other underwater vessels which pose new threats such as terrorism and smuggling. To detect these vessels, an advanced underwater sensor network is necessary. Such sensors can measure fluctuations in for example, magnetic and electric fields, pressure changes, and acoustics. Deploying an underwater sensor in its predetermined position can be di cult due to currents, surge, and the lack of a Global Navigation Satellite System (GNSS) functioning underwater. Sometimes the sensors must be deployed fast, resulting in very uncertain sensor positions. These positions must then be estimated in order to enable the network to accurately track an alien vessel. Lately, many solutions to the underwater sensor local- ization problem have been suggested. They can be broadly divided into two major categories: range-based and range- free. In general, range-based schemes provide more accurate positioning than range-free schemes. Range-based schemes use information about the range or angle between sensors. The problem is thereafter for- mulated as a multilateral problem. Common methods to measure range or angle include Time of Arrival (ToA), Time Di ff erence of Arrival (TDoA), Angle of Arrival (AoA), or Received Signal Strength Indicator (RSSI). These methods
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