The effects of time‐gating and radiation correction on virtual source data

Abstract

In the Virtual Source (VS) method we cross-correlate seismic recordings at two receiver locations to create a new data set as if one of these receivers is a Virtual Source and the other is a receiver. We evaluate the amplitude and phase spectra of VS data, generated in a laterally invariant medium, in the FK-domain. It is shown that phase information is accurately retrieved, whereas amplitudes are subject to an imprint of the overburden. This imprint, which can be interpreted as the VS amplitude radiation pattern, can be estimated by auto-correlation of the downgoing wave field that was used for VS creation. We can optimize the radiation characteristics by spatial deconvolution with the estimated radiation pattern. Another strategy is to apply time-gating to the downgoing wave field, as is commonly applied in the current best practice of the VS method. We offer an explanation why time-gating indeed enhances the amplitude radiation characteristics of VS data, while having minor influences on the phase spectrum. It can be argued that the phase is best retrieved if the correlated signals have long recording times, as multiple scattering will be most effectively exploited. We show how phase information from total field correlations can be combined with amplitude information from timegated fields to improve the phase spectrum without deteriorating the amplitudes. Finally, we show how timegating and amplitude radiation correction through spatial deconvolution can be combined.