Abstract: A temperature sensing method in which pulses of optical radiation are launched by a laser diode (11) into an optical fibre (14) and optical radiation backscattered from the fibre is detected, the method comprising passing the backscattered radiation through a single optical filter (15) whereby a first signal is recorded at the anti-Stokes Raman wavelength from a signal launched by laser diode in a laser mode and a second signal is recorded at the Rayleigh wavelength from a signal launched by the laser diode in a light emitting diode mode, and a comparison is made of the two signals to provide an indication of temperature.