Optical fibre distributor sensor

An optical fibre distributed sensing system, e.g. for temperature, includes a multi-channel averaging circuit arrangement comprising an analogue-to-digital converter 10 which receives an analogue electrical input corresponding to back-scattered or returned light along an optical fibre sensor 5. The digital output therefrom is fed sequentially to respective digital storage devices 11 of a digital storage arrangement and the data stored for corresponding elements of each back-scattered or returned light signal is then clocked out simultaneously into a digital adder 15. The output from the adder is fed to a processor 24 for providing an indication of the averaged signal waveform in respect of successive waveforms with reduced noise.