1. Ashdown, C., 2000. Mains Location Equipment – A State of the Art Review and Future Research Needs. UKWIR Report (Reference Number 01/WM/06/1).
2. Gucunski, N., Krstic, V., Maher, A., 2000. Field implementation of the surface waves for obstacle detection (SWOD) method. In: Proc 15th World Conference on Nondestructive Testing, Roma, Italy.
3. The elastic stresses produced by the indentation of the plane surface of a semi-infinite elastic solid by a rigid punch;Harding;Proceedings of the Cambridge Philosophical Society,1945
4. Fundamentals of Acoustics;Kinsler,1982
5. Mapping the Underworld, 2011. (accessed July 2011).