A method and a system are provided, in which acoustic signals received by distributed acoustic sensors are processed in order to determine the position of a source or sources of the acoustic signals. The method and system are able to determine the position of several acoustic sources simultaneously, by measuring the corresponding several acoustic signals. Furthermore, the strength of the acoustic signal or signals can be determined. The location of the acoustic source may be overlaid on a map of an area being monitored, or be used to generate an alarm if perceived to correspond to a threat or an intrusion, for example in a pipeline monitoring application. Alternatively, the method and systems can be used to monitor a hydraulic fracturing process.