Quadrature signals Q and in-phase signals I output from a pathlength mismatched interferometric sensor are normalized sampling the signals to obtain a first set of values Q.sub.k =Q.sub.0 B.sub.k sin .phi..sub.k corresponding to the sine of the phase shift and a second set of values I.sub.k =I.sub.0 B.sub.k cos .phi..sub.k corresponding to the cosine of the phase shift where k is a running index of the set of consecutive samples of Q and I. A quantity DQ.sub.k =.vertline.(Q.sub.u(k)).sup.2 -(Q.sub.s(k)).sup.2 .vertline. is calculated for the quadrature signals; and a quantity DI.sub.k =.vertline.(I.sub.u(k)).sup.2 -(I.sub.s(k)).sup.2 .vertline. is calculated for the in-phase signals, where u(k) and s(k) are parameters used to determine indices that select specific sampled signals and k is a running index of the set of consecutive samples of Q and I. The normalization factor is then calculated as the ratio R=Q.sub.N /I.sub.N where ##EQU1##