A method for estimating a time variant signal representing a seismic source obtains seismic data recorded by at least one receiver and generated by the seismic source, the recorded seismic data comprising direct arrivals and derives the time variant signal using an operator that relates the time variant signal to the acquired seismic data, the operator constrained such that the time variant signal is sparse in time.

Methods and systems for processing data acquired using a variable-depth streamer, obtain up-going and down-going wavefields at a predetermined datum, and use them to identify multiples included in the up-going wavefield. An image of a geological formation under the seabed is then generated using the data from which the multiples have been removed, and/or the multiples.

Noise can be attenuated in marine seismic data from a marine seismic survey. A first near-continuous measurement of a wavefield and a second near-continuous measurement of the wavefield recorded from a marine seismic survey can be equalized, a coherent portion of the equalized second near-continuous measurement can be collapsed, and a noise model can be derived. The noise model can be subtracted from the second near-continuous measurement.

An offshore reservoir monitoring system (100) comprises a vertical array (110) with multiple seismic receivers (120) less than 10 m apart. During operation, the vertical array is deployed in a shallow borehole (111) in a seabed (10) away from noise at a seafloor (11). The dense spacing of receivers (120) ensures an adequate number of sensors (120) in the shallow borehole (111) and a spatial sampling rate appropriate for suppressing coherent noise in the shallow layers under the seafloor (11). Vertical arrays (110) can be added to the system (100) at any time.

Methods and systems for optimized receiver-based ghost filter generation are described. The optimized ghost filter self-determines its parameters based on an iterative calculation of recorded data transformed from a time-space domain to a Tau-P domain. An initial ghost filter prediction is made based on generating mirror data from the recorded data and using a least squares technique during a premigration stage.

A method comprising for deghosting seismic data is disclosed. The method includes the steps of acquiring seismic data by conducting a survey of a subsurface area of interest wherein the seismic data includes ghost data and estimating a time-varying wave height above the subsurface area of interest during at least a portion of the survey, wherein the estimation of the wave height is based at least in part on a remote measurement of the wave height during the survey. The estimated time-varying wave height is used to characterize the ghost data and deghost the seismic data based at least in part on the characterized ghost data.

Wavefield separation methods and systems that adjust near-continuous pressure and particle motion wavefields based on distance moved along a vessel track by the sensors when the wavefields were measured are disclosed. Methods and systems correct for the motion of the receivers in towed streamer seismic data in order to obtain a wavefield with approximately stationary-receiver locations. Wavefield separation may then be applied to the wavefield with approximately stationary-receiver locations.

A method for estimating a far field seismic energy source signature includes using detected near field seismic signals corresponding to actuation of each one of a plurality of seismic energy sources in an array of seismic energy sources. The near field seismic signals are detected at two spaced apart locations in the near field of each seismic energy source, the at least two spaced apart locations being arranged such that a direction of propagation of the detected near field seismic signals is determinable from the detected near field signals. A notional source signature for each seismic energy source and a notional ghost for each seismic energy source using the detected near field seismic signals. A far field signature is determined for the plurality of seismic energy sources using the determined notional source signature and notional ghost signature from each seismic energy source.

Apparatus, computer instructions and method for separating up-going and down-going wave fields (U, D) from seismic data recorded within or beneath a body of water, or in general below the surface of the earth. The method includes a step of receiving seismic data (P.sub.o, Z.sub.o) recorded in the time-space domain with seismic recorders distributed on a first datum, wherein the first datum is non-flat; a step of establishing a mathematical relation between transformed seismic data (P, Z) and the up-going and down-going wave fields (U, D) on a second planar datum; and a step of solving with an inversion procedure, run on a processor, the mathematical relation to obtain the up-going and down-going wave fields (U, D) for the second datum. The second datum is different from the first datum.

Prediction and subtraction of multiple diffractions may include transforming previously acquired seismic data from a time-space domain to a transformed domain using a dictionary of compressive basis functions and separating, within the transformed previously acquired seismic data, a first portion and a second portion of the transformed previously acquired seismic data. Prediction and subtraction of multiple diffractions may also include predicting a plurality of multiple diffractions based on the separated first and second portions and adaptively subtracting the predicted multiple diffractions from the previously acquired seismic data. Prediction and subtraction of multiple diffractions may also include inverse transforming a particular seismic data set from the transformed domain to the time-space domain.