An apparatus for estimating a parameter includes: an optical fiber sensor including at least one optical fiber configured to be disposed in a downhole location and including at least one sensing location configured to generate measurement signals; at least one light source configured to transmit a measurement signal having a wavelength to interrogate a sensing location and cause the sensing location to return a reflected measurement signal indicative of a measured parameter, and configured to transmit a reference signal and cause a reflected reference signal to be returned from a location associated with the sensing location, the reflected reference signal having a known relationship to hydrogen concentration; and a processor configured to receive the reflected measurement signal and the reflected reference signal, estimate the hydrogen concentration based on the reflected reference signal, and calibrate the first reflected signal based on the estimated hydrogen concentration.