Abstract: This application describes methods and apparatus for monitoring of rail networks using fibre optic distributed acoustic sensing (DAS), especially for condition monitoring. One method involves taking (902) a first data set corresponding to measurement signals from a plurality of channels of at least one fibre optic distributed acoustic sensor (100) having a sensing fibre (101) deployed to monitor at least part of the path of the rail network (201). The first data set corresponds to measurement signals acquired as a train (202) passed along a first monitored section of the rail network. The method involves identifying (903) a speed of the train through the first monitored section and dividing (904) the first data set into a plurality of time windows. Each time window contains a different subset of the first data set, with the measurement signal for each successive channel in a time window being delayed with respect to the previous channel by a time related to the identified train speed.

Abstract: This application describes methods and apparatus for monitoring of rail networks using fibre optic distributed acoustic sensing (DAS), especially for condition monitoring. One method involves taking (902) a first data set corresponding to measurement signals from a plurality of channels of at least one fibre optic distributed acoustic sensor (100) having a sensing fibre (101) deployed to monitor at least part of the path of the rail network (201). The first data set corresponds to measurement signals acquired as a train (202) passed along a first monitored section of the rail network. The method involves identifying (903) a speed of the train through the first monitored section and dividing (904) the first data set into a plurality of time windows. Each time window contains a different subset of the first data set, with the measurement signal for each successive channel in a time window being delayed with respect to the previous channel by a time related to the identified train speed.

Abstract: Methods and apparatus for interferometric seismic imaging and creation of a high-resolution three-dimensional seismic volume in proximity to a wellbore are described. In contrast to current methods that deliver positions of microseismic events using a small fraction of the microseismic wavefield, the present invention provides for the analysis of a full microseismic wavefield. In a preferred embodiment, the method includes creating a planar image slice and/or corridor between the location of one or more microseismic events and one or several sensor arrays to produce a multitude of azimuthally orientated planar image slices and/or corridors. The method further includes adding the planar image slice and/or corridor contributions to create a single three-dimensional volume for analysis and rendering.