Abstract: A measurement is carried out on a medium that propagates energy in a selected form by applying energy in the selected form to the medium, the power varying as a function of time in accordance with the elements of two Golay complementary sequences where one kind of element is represented by zero power and the other kind of element is represented by a predetermined non-zero power level and the successive elements of each sequence are applied at uniform intervals. Energy emitted from the medium in the selected form is received, and the variation as a function of time of the power emitted is correlated with the variation as a function of time of the power that was applied. Preferably, the level at which power is applied is varied both directly, in accordance with the elements of the two Golay complementary sequences, and in a derivative fashion, in accordance with the logical complements of the two Golay complementary sequences.