AVO modeling with non-zero phase spherical waves
Charles P. Ursenbach, Arnim B. Haase
Spherical-wave reflection coefficients are normally calculated using a zero-phase wavelet. The purpose of this study is to clarify whether phase affects reflectivity, and to explain the observed results. Numerical experiments show that zero-phase, rotated-phase, and linear-phase wavelets give identical reflectivities, but that minimum-phase wavelets give slightly different AVO results in a region beyond the critical angle, even though they share the same amplitude spectrum. Expressing the reflectivity calculation as a weighted integral of plane-wave coefficients provides insight into these results. The weighting functions for zero- and minimum-phase wavelets differ from each other. In particular, although the central part of the weighting does not differ appreciably, the edges differ significantly in ways that mimic the differences between reflection coefficient curves.