Vehicle Detection and Analysis on Bridge with $\varphi$-OTDR

We present an on-field implementation of a distributed acoustic optical fiber sensor based on phase optical time domain reflectometry (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\boldsymbol{\varphi}$</tex>-OTDR) as a vehicle detection system for a bridge in the Netherlands, showing how it is capable of detecting passing vehicles, as well as their number of axles and their speed.