The paper shows that optical fibre sensors and distributed fibre sensors in particular can be analysed by direct analogy to guided wave radar systems. This shows that all optical fibre sensor measurements can be represented as 4 basic types of measurement corresponding to time and frequency derivatives of the transmission or reflection coefficient of the fibre transmission line. This approach is used to explain and aid the understanding of both distributed optical fibre sensors (OTDR) and passive multiplexing of many fibre sensors. It also indicates the relations between some of the key parameters involved, including source coherence, range resolution, the bandwidth/repetition rate of the associated optical modulation. The particular approach is extendable to various configurations of optical fibre network and is applicable to both single mode and multimode systems.