  Underwater monitoring and surveillance systems are essential for underwater
target detection, localization and classification. The aim of this work is to
investigate the possibility of target detection by using data transmission
between communication nodes in an underwater acoustic (UWA) network, i.e,
re-using acoustic communication signals for target detection. A new target
detection method based on estimation of the time-varying channel impulse
response between the communication transmitter(s) and receiver(s) is proposed
and investigated. This is based on a lake experiment and numerical experiments
using a simulator developed for modeling the time-varying UWA channel in the
presence of a moving target. The proposed detection method provides a clear
indication of a target crossing the communication link. A good similarity
between results obtained in the numerical and lake experiments is observed.
