1. A method for detecting, identifying and locating an event representing a failure mode and/or a precursor to a failure mode within a pipeline segment or network, comprising: using an acoustic sensor acoustically coupled to the pipeline segment or network, detecting a passive acoustic signal from the pipeline segment or network; using an acoustic transmitter acoustically coupled to the pipeline segment or network, transmitting an active acoustic signal to the pipeline segment or network; using the same or a different acoustic sensor acoustically coupled to the pipeline segment or network, detecting the active acoustic signal from the pipeline segment or network; and processing both the passive acoustic signal and the active acoustic signal to characterize an anomaly within the pipeline segment or network.