Reciprocity properties of one-way propagators

Acoustic reciprocity is a fundamental property of the wave equation for the total acoustic wavefield (Rayleigh, 1878). In its most elementary form the reciprocity principle states that an acoustic response remains the same when the source and receiver are interchanged. In terms of Green's functions this reciprocity principle reads G(r2, r1) = G(r1, r2), with r = (x, y, z). For more general expressions and their seismic applications, see Fokkema and van den Berg (1993).