  Node localization plays an important role in many practical applications of
wireless underground sensor networks (WUSNs), such as finding the locations of
earthquake epicenters, underground explosions, and microseismic events in
mines. It is more difficult to obtain the time-difference-of-arrival (TDOA)
measurements in WUSNs than in terrestrial wireless sensor networks because of
the unfavorable channel characteristics in the underground environment. The
robust Chinese remainder theorem (RCRT) has been shown to be an effective tool
for solving the phase ambiguity problem and frequency estimation problem in
wireless sensor networks. In this paper, the RCRT is used to robustly estimate
TDOA or range difference in WUSNs and therefore improves the ranging accuracy
in such networks. After obtaining the range difference, distributed source
localization algorithms based on a diffusion strategy are proposed to decrease
the communication cost while satisfying the localization accuracy requirement.
Simulation results confirm the validity and efficiency of the proposed methods.
