366 ◾ Risk Assessment and Security
of the ber-based BOTDR sensors to detect soil strains (Klar and Linker 2009).
e proposed detection system is based on wavelet decomposition of the BOTDR
signal followed by a neutral network (Klar and Linker 2009). Further research
stages, and in particular eld validation tests, are still required before such a system
could become fully operational (Klar and Linker 2009).
Currently, tunnel detection technology risks (Shi 2011) include the following:
(1) GPR may be ineective in many urban environments; (2) unfavorable geophysi-
cal/geological conditions may limit detection; and (3) depth/dimensions of tunnels
are highly variable, with small footprint. For future plans in detecting illegal tun-
nels, the followi ...