There is described a sensor apparatus. It comprises an interrogator comprising a light source emitting pulses having a wavelength about an average wavelength; and a fiber Bragg grating (FBG) arrangement. The arrangement comprises a FBG sensor array comprising a plurality of FBG sensors on an optical fiber and being for reflecting the pulses, thereby producing reflected pulses at each one of the FBG sensors. FBG sensors of a given FBG sensor array have a spatial separation therebetween which is sufficient to allow, at a receiver, a temporal discrimination between the reflected pulses produced by each one of the FBG sensors. The FBG sensor array has a spectral reflection window which comprises the average wavelength.