Abstract: Disclosed are apparatus and methods for seismic exploration using pressure changes caused by sea-surface variations as a low-frequency seismic energy source. One embodiment relates to a method which obtains dual wave-fields measured below a sea surface. The measured dual wave-fields are decomposed into a down-going wave-field and an up-going wave-field at a selected observation level. Seismic images are then generated using the down-going and up-going wave-fields. Other embodiments, aspects, and features are also disclosed.

Abstract: A measured pressure field, a measured vertical velocity field, and two measured orthogonal horizontal velocity fields are obtained. A programmable computer is used to perform the following. A scaling factor is determined from water acoustic impedance, the measured pressure field, and the horizontal velocity fields. One of the measured pressure field and measured vertical velocity field is combined with one of the measured vertical velocity field scaled by the scaling factor and the measured pressure field scaled by the scaling factor, generating one of up-going and down-going pressure and velocity wavefields.

Abstract: A pressure wavefield and a normal velocity wavefield measured on a smoothly shaped acquisition surface by towed dual-sensor marine seismic streamers are decomposed into up-going and down-going pressure and particle velocity components on an observation level between the acquisition surface and a sea surface of undetermined shape. The up-going and down-going pressure and particle velocity components are extrapolated iteratively in steps from the observation level toward the sea surface. An image point and a reflection coefficient of the sea surface at the image point are determined from the iteratively extrapolated up-going and down-going pressure and particle velocity components.

Abstract: Signals detected by particle motion sensors in a towed dual sensor marine seismic streamer are scaled to match signals detected by pressure sensors in the streamer. The pressure sensor signals and the scaled particle motion sensor signals are combined to generate up-going and down-going pressure wavefield components. The up-going and down-going pressure wavefield components are extrapolated to a position just below a water surface. A first matching filter is applied to the extrapolated down-going pressure wavefield component. The filtered down-going pressure wavefield component is subtracted from the extrapolated up-going pressure wavefield component, generating an up-going pressure wavefield component with attenuated particle motion sensor noise. A second matching filter is applied to the extrapolated up-going pressure wavefield component.

Abstract: Three data subsets are obtained in three selected azimuthal directions from seismic data in heterogeneous, anisotropic media. Azimuthal velocities are determined for each of the data subsets. A linear system of equations in the three selected azimuthal directions and the three determined azimuthal velocities is solved for three independent parameters. An azimuthal time migration velocity function is constructed from the three solved independent parameters. A time migration traveltime function is constructed from the constructed azimuthal time migration velocity function.

Abstract: A pressure wavefield and a normal velocity wavefield measured on a smoothly shaped acquisition surface by towed dual-sensor marine seismic streamers are decomposed into up-going and down-going pressure and particle velocity components on an observation level between the acquisition surface and a sea surface of undetermined shape. The up-going and down-going pressure and particle velocity components are extrapolated iteratively in steps from the observation level toward the sea surface. An image point and a reflection coefficient of the sea surface at the image point are determined from the iteratively extrapolated up-going and down-going pressure and particle velocity components.

Abstract: Particle motion sensor signals and the pressure sensor signals data from a towed marine seismic streamer are combined to generate an up-going pressure wavefield component and a down-going particle motion wavefield component. The down-going particle motion wavefield component is extrapolated from the receiver position depth level to the source position depth level. The up-going pressure wavefield component is multiplied by the extrapolated down-going particle motion wavefield component, generating a first product. Then, nth order surface related multiples in the pressure wavefield are iteratively calculated utilizing a product of (n?1)th surface related multiple free data and the extrapolated down-going particle motion wavefield component. The calculated nth order surface related multiples are iteratively subtracted from the recorded pressure wavefield, generating the nth order surface related multiple free data.

Abstract: Particle motion sensor signals and the pressure sensor signals data from a towed marine seismic streamer are combined to generate an up-going pressure wavefield component and a down-going particle motion wavefield component. The down-going particle motion wavefield component is extrapolated from the receiver position depth level to the source position depth level. The up-going pressure wavefield component is multiplied by the extrapolated down-going particle motion wavefield component, generating a first product. Then, nth order surface related multiples in the pressure wavefield are iteratively calculated utilizing a product of (n?1)th surface related multiple free data and the extrapolated down-going particle motion wavefield component. The calculated nth order surface related multiples are iteratively subtracted from the recorded pressure wavefield, generating the nth order surface related multiple free data.

Abstract: Three data subsets are obtained in three selected azimuthal directions from seismic data in heterogeneous, anisotropic media. Azimuthal velocities are determined for each of the data subsets. A linear system of equations in the three selected azimuthal directions and the three determined azimuthal velocities is solved for three independent parameters. An azimuthal time migration velocity function is constructed from the three solved independent parameters. A time migration traveltime function is constructed from the constructed azimuthal time migration velocity function.

Abstract: Signals detected by particle motion sensors in a towed dual sensor marine seismic streamer are scaled to match signals detected by pressure sensors in the streamer. The pressure sensor signals and the scaled particle motion sensor signals are combined to generate up-going and down-going pressure wavefield components. The up-going and down-going pressure wavefield components are extrapolated to a position just below a water surface. A first matching filter is applied to the extrapolated down-going pressure wavefield component. The filtered down-going pressure wavefield component is subtracted from the extrapolated up-going pressure wavefield component, generating an up-going pressure wavefield component with attenuated particle motion sensor noise. A second matching filter is applied to the extrapolated up-going pressure wavefield component.