1. A method for detecting and identifying 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 subsequent to the acoustic sensor detecting the passive acoustic signal from 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.