Monitoring traffic flow

Abstract

This application relates to apparatus and methods for traffic monitoring, especially for monitoring of road traffic flow using fiber optic distributed acoustic sensing. The method involves performing distributed acoustic sensing (DAS) using a suitable interrogator unit () to provide a measurement signal from each of a plurality of sensing portions of a first length of a sensing optical fiber (), where the first length of the sensing optical fiber runs alongside a road () having a plurality of lanes. The measurement signals from the sensing portions are processed to detect vehicles () travelling on the road and to determine at least one detected traffic flow property. The method further involves using a traffic flow model to relate the detected flow property to a modelled flow property, where the traffic flow model is configured to model vehicle detections that will be missed by the distributed acoustic sensing i.e. an indication of vehicles present on the road but not detected by the DAS sensor.