Seismic forward modeling and reverse time migration of order-separated free surface multiples using dipole source approximation

Conventional reverse time migration using order-separated free surface multiples (RTMOSM) was developed to eliminate crosstalk from unrelated-order multiples through cross-correlation of adjacent-order multiples. The (n-1)th-order multiples are directly injected into the forward modeling procedure as an areal source to generate the nth-order multiples in this imaging framework. The generated nth-order multiples exhibit accurate traveltime, but the amplitude and phase are inaccurate due to improper handling of reflection on the free surface. This inaccuracy can negatively affect the cross-correlation between the forward- and back-propagated multiple wavefields. To resolve this limitation, we propose a dipole-source reverse time migration of order-separated free surface multiples (DRTMOSM) by introducing a free surface reflection operator into the areal source within the forward modeling procedure. The reflection operator acts as a dipole approximation of the free surface, representing a composite of the incident wave and its reflected wave (ghost). The proposed method offers a more complete representation of the reflection effect on the free surface, allowing for more accurate simulations of multiples within the RTM framework’s forward modeling procedure. This improvement leads to a higher imaging resolution and a broader effective frequency bandwidth in the imaging domain.