Wireless underground sensor networks: Research challenges Ian F. Akyildiz * , Erich P. Stuntebeck Broadband and Wireless Networking Laboratory, School of Electrical and Computer Engineering, Georgia Institute of Technology, 75 5th St. NW, Atlanta, GA 30308, United States Received 31 January 2006; received in revised form 20 April 2006; accepted 3 July 2006 Available online 12 July 2006 Abstract This work introduces the concept of a Wireless Underground Sensor Network (WUSN). WUSNs can be used to mon- itor a variety of conditions, such as soil properties for agricultural applications and toxic substances for environmental monitoring. Unlike existing methods of monitoring underground conditions, which rely on buried sensors connected via wire to the surface, WUSN devices are deployed completely belowground and do not require any wired connections. Each device contains all necessary sensors, memory, a processor, a radio, an antenna, and a power source. This makes their deployment much simpler than existing underground sensing solutions. Wireless communication within a dense substance such as soil or rock is, however, significantly more challenging than through air. This factor, combined with the necessity to conserve energy due to the difficulty of unearthing and recharging WUSN devices, requires that communication pro- tocols be redesigned to be as efficient as possible. This work provides an extensive overview of applications and design challenges for WUSNs, challenges for the underground communication channel including methods for predicting path losses in an underground link, and challenges at each layer of the communication protocol stack. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Wireless sensor networks; Underground sensing 1. Introduction Sensor networks are currently a very active area of research. The richness of existing and potential applications from commercial agriculture and geol- ogy to security and navigation has stimulated signif- icant attention to their capabilities for monitoring various underground conditions. In particular, agri- culture uses underground sensors to monitor soil conditions such as water and mineral content [1]. Sensors are also successfully used to monitor the integrity of belowground infrastructures such as plumbing [32], and landslide and earthquake moni- toring are accomplished using buried seismometers [13]. The current technology for underground sensing consists of deploying a buried sensor, such as that shown in Fig. 1, and wiring it to a data-logger on the surface which stores sensor readings for later 1570-8705/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.adhoc.2006.04.003 * Corresponding author. Tel.: +1 404 894 5141; fax: +1 404 894 7883. E-mail addresses: ian@ece.gatech.edu (I.F. Akyildiz), eps@ ece.gatech.edu (E.P. Stuntebeck). Ad Hoc Networks 4 (2006) 669–686 www.elsevier.com/locate/adhoc