An acoustic method of providing spatial and temporal classification of a range of different types of sound producing targets in a geographical area, the method including the steps of: creating a number of virtual dedicated sensing and monitoring optical fibre networks formed by virtual sensing lines created by selecting segments from a plurality of optical fibres distributed across the geographical area and forming at least part of a pre-existing installed fibre-optic communications network made up of a number of different fibre optic cables; creating a plurality of different footprints in the geographic area, each footprint being associated with an entity or subscriber and comprising at least one of the created virtual dedicated sensing and monitoring optical fibre network; repeatedly transmitting, at multiple instants, interrogating optical signals into each of the plurality of optical fibres from which segments have been selected; receiving, during an observation period following each of the multiple instants, returning optical signals scattered in a distributed manner over distance along the plurality of optical fibres, the scattering influenced by acoustic disturbances caused by the multiple targets within the observation period; demodulating acoustic data from the received optical signals; processing the demodulated acoustic data and classifying it in accordance with the target classes or types to generate a plurality of datasets including classification, temporal and location-related data; storing the plurality of datasets in parallel with the demodulated acoustic data which is time and location stamped so that it can be retrieved for further processing and matched with the corresponding plurality of datasets to provide both real time and historic data; and monitoring the plurality of different footprints in the geographic area, comprising obtaining at least location related data associated with each footprint and processing this data with that of the generated plurality of datasets to provide dedicated datasets associated with each footprint, the location related data corresponding to the at least one of the created virtual dedicated sensing and monitoring optical fibre network. creating a number of virtual dedicated sensing and monitoring optical fibre networks formed by virtual sensing lines created by selecting segments from a plurality of optical fibres distributed across the geographical area and forming at least part of a pre-existing installed fibre-optic communications network made up of a number of different fibre optic cables; creating a plurality of different footprints in the geographic area, each footprint being associated with an entity or subscriber and comprising at least one of the created virtual dedicated sensing and monitoring optical fibre network; repeatedly transmitting, at multiple instants, interrogating optical signals into each of the plurality of optical fibres from which segments have been selected; receiving, during an observation period following each of the multiple instants, returning optical signals scattered in a distributed manner over distance along the plurality of optical fibres, the scattering influenced by acoustic disturbances caused by the multiple targets within the observation period; demodulating acoustic data from the received optical signals; processing the demodulated acoustic data and classifying it in accordance with the target classes or types to generate a plurality of datasets including classification, temporal and location-related data; storing the plurality of datasets in parallel with the demodulated acoustic data which is time and location stamped so that it can be retrieved for further processing and matched with the corresponding plurality of datasets to provide both real time and historic data; and monitoring the plurality of different footprints in the geographic area, comprising obtaining at least location related data associated with each footprint and processing this data with that of the generated plurality of datasets to provide dedicated datasets associated with each footprint, the location related data corresponding to the at least one of the created virtual dedicated sensing and monitoring optical fibre network.