Analysis of Optical Fading In Phase-OTDR Distributed Acoustic Sensing Systems: The Effects of Fading in Threat Detection

Abstract

Signal fading is a widely observed phenomenon in communication and sensing applications that results in spatially and temporally varying degradations in the received signal power. Specifically, for distributed acoustic sensing (DAS) applications based on phase sensitive Optical Time Domain Reflectometry (phase-OTDR), it is reported that optical signal fading is observed as random dramatic signal power fluctuations, which in turn cause substantial variations in threat detection sensitivity. In this paper, we study optical signal fading in the context of phase-OTDR based DAS from a signal processing perspective and analyze the undesired effects of fading on threat detection performance. Using a detailed phase-OTDR signal model, we analyze the effects of internal system parameters and external vibration source characteristics on optical fading. Based on these analyses, we define the conditions under which optical fading can manifest itself as a dramatic variation in threat detection performance.