Signal fading analysis for φ-OTDR applied in vehicle detection

We present a study on the occurrence of signal fading in a φ-OTDR sensor employing a linear-nonlinear preamplification system. After presenting a method to evaluate the incidence of fading, we test how the latter can be minimized by different values of pulse width, both in the laboratory and on a highway bridge in the Netherlands. In addition, we show how this analysis of acoustically induced strain, induced by the passing vehicles, allowed for detection of the number of wheels of the vehicles passing over the bridge.