A sensor system comprising: a sensor array generating a plurality of frequency separated component optical carrier signals (710A, 710B, 710C) forming together an optical signal conveyed by an optical transmission means; a phase modulation signal generator for generating a phase modulation signal, the phase modulation signal generator including a pseudorandom binary sequence signal generator to generate a pseudorandom binary sequence signal; an interferometer comprising a first optical path and a second optical path for both receiving the optical signal, wherein the first optical path includes an optical modulator to receive the optical signal and form a phase modulated optical signal in accordance with the phase modulation signal, the first optical path further including respective wavelength selective reflectors (725A, 725B, 725C) for introducing a respective time delay for each frequency separated component optical signal (710A, 710B, 710C) of the phase modulated optical signal to be then combined on reflection with the optical signal from the second optical path to form a combined optical intensity signal; a photodetector to measure an intensity of the combined optical intensity signal from the interferometer and to generate a time varying electrical detector signal; an analog to digital convertor to convert the time varying electrical detector signal to a time varying digitized detector signal; a decorrelator arrangement including a plurality of decorrelation channels corresponding to each of the frequency separated component optical signals (710A, 710B, 710C), each decorrelation channel receiving as an input the time varying digitized detector signal from the analog to digital converter and operable to recover a phase modulated component signal (795A, 795B, 795C) corresponding to an individual frequency separated component optical carrier signal (710A, 710B, 710C) based on the respective time delay for that frequency separated component optical carrier signal (710A, 710B, 710C) introduced by the respective wavelength selective reflector (725A, 725B, 725C) and the pseudorandom binary sequence signal; and a demodulator arrangement including a plurality of demodulation channels to demodulate each phase modulated component signal (795A, 795B, 795C) to determine the individual frequency variations of the plurality of frequency separated component optical carrier signals (710A, 710B, 710C). a sensor array generating a plurality of frequency separated component optical carrier signals (710A, 710B, 710C) forming together an optical signal conveyed by an optical transmission means; a phase modulation signal generator for generating a phase modulation signal, the phase modulation signal generator including a pseudorandom binary sequence signal generator to generate a pseudorandom binary sequence signal; an interferometer comprising a first optical path and a second optical path for both receiving the optical signal, wherein the first optical path includes an optical modulator to receive the optical signal and form a phase modulated optical signal in accordance with the phase modulation signal, the first optical path further including respective wavelength selective reflectors (725A, 725B, 725C) for introducing a respective time delay for each frequency separated component optical signal (710A, 710B, 710C) of the phase modulated optical signal to be then combined on reflection with the optical signal from the second optical path to form a combined optical intensity signal; a photodetector to measure an intensity of the combined optical intensity signal from the interferometer and to generate a time varying electrical detector signal; an analog to digital convertor to convert the time varying electrical detector signal to a time varying digitized detector signal; a decorrelator arrangement including a plurality of decorrelation channels corresponding to each of the frequency separated component optical signals (710A, 710B, 710C), each decorrelation channel receiving as an input the time varying digitized detector signal from the analog to digital converter and operable to recover a phase modulated component signal (795A, 795B, 795C) corresponding to an individual frequency separated component optical carrier signal (710A, 710B, 710C) based on the respective time delay for that frequency separated component optical carrier signal (710A, 710B, 710C) introduced by the respective wavelength selective reflector (725A, 725B, 725C) and the pseudorandom binary sequence signal; and a demodulator arrangement including a plurality of demodulation channels to demodulate each phase modulated component signal (795A, 795B, 795C) to determine the individual frequency variations of the plurality of frequency separated component optical carrier signals (710A, 710B, 710C).