Underwater acoustic sensor networks: research challenges Ian F. Akyildiz * , Dario Pompili, Tommaso Melodia Broadband and Wireless Networking Laboratory, School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA Received 15 July 2004; received in revised form 20 September 2004; accepted 21 January 2005 Available online 2 February 2005 Abstract Underwater sensor nodes will find applications in oceanographic data collection, pollution monitoring, offshore exploration, disaster prevention, assisted navigation and tactical surveillance applications. Moreover, unmanned or autonomous underwater vehicles (UUVs, AUVs), equipped with sensors, will enable the exploration of natural under- sea resources and gathering of scientific data in collaborative monitoring missions. Underwater acoustic networking is the enabling technology for these applications. Underwater networks consist of a variable number of sensors and vehi- cles that are deployed to perform collaborative monitoring tasks over a given area. In this paper, several fundamental key aspects of underwater acoustic communications are investigated. Different archi- tectures for two-dimensional and three-dimensional underwater sensor networks are discussed, and the characteristics of the underwater channel are detailed. The main challenges for the development of efficient networking solutions posed by the underwater environment are detailed and a cross-layer approach to the integration of all communication functionalities is suggested. Furthermore, open research issues are discussed and possible solution approaches are outlined. Ó 2005 Published by Elsevier B.V. Keywords: Underwater acoustic sensor networks; Underwater networking; Acoustic communications 1. Introduction Underwater sensor networks are envisioned to enable applications for oceanographic data col- lection, pollution monitoring, offshore explora- tion, disaster prevention, assisted navigation and tactical surveillance applications. Multiple unmanned or autonomous underwater vehicles (UUVs, AUVs), equipped with underwater sen- sors, will also find application in exploration of natural undersea resources and gathering of scientific data in collaborative monitoring mis- sions. To make these applications viable, there is a need to enable underwater communications 1570-8705/$ - see front matter Ó 2005 Published by Elsevier B.V. doi:10.1016/j.adhoc.2005.01.004 * Corresponding author. Tel.: +1 404 894 5141; fax: +1 404 894 7883. E-mail addresses: ian@ece.gatech.edu (I.F. Akyildiz), dar- io@ece.gatech.edu (D. Pompili), tommaso@ece.gatech.edu (T. Melodia). Ad Hoc Networks 3 (2005) 257–279 www.elsevier.com/locate/adhoc