Recent incidences of sabotage of Oil and Gas pipelines in the Baltic Sea have made it clear that sub-sea pipelines are vulnerable and will require surveillance for protection. Harbors and ports are noisy. Pressure measurements from hydrophones allow only measurements of signal arrival times. With only this information, a dense, spatially dispersed sensor array is required for detection and localization. Using vector sensors allow additional estimation of direction of propagation at each measurement point, allowing separating signals from multiple sources. A smaller number of vector sensors can replace a larger number of scalar pressure sensors. Static sea-floor deployment of the sensor array, allows accurate mapping after deployment, reducing inaccuracies in sensor locations found in mobile systems. We describe a method that allows using multi-component sea-floor sensors to identify and track any source of acoustic energy even when the orientations of the multi-component sensors are unknown. Sources that satisfy certain simple assumptions can be used to find the absolute orientation of the multi-component sensors. The methodology allows using a simplified sensor array where a short-interval fiber-optic DAS array is combined with a sparse array of two-component, transverse-only, point sensors. We describe optical multi-component accelerometers, that are easily combinable with DAS sensor arrays. Without electronics, there is no need for power - and the risk of failure of electronics left for a long period of time is eliminated, significantly increasing the lifetime of the installation. The acquisition system for the hybrid optical array will be simpler and enable “always-on” monitoring.
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