This paper will describe techniques which should greatly reduce the signal averaging times required in conventional distributed Optical Time Domain Reflectometry (OTDR) sensor systems. The technique does not require coherent detection and spectral analysis as is currently used in FMCW or FMAMCW. A digitally generated pseudo-random noise sequence is modulated on to a light source and transmitted down an optical fibre. The received backscattered signal is then correlated (multiplied) with a delayed version of the transmitted sequence to evaluate the amplitude of the backscattered signal at a given point along the fibre. The average transmitted and received signal power is therefore increased allowing reduced signal averaging times or reduced peak laser powers to be used compared with conventional OTDR systems.