| In marine towed acquisition,the receivers record not only the up-going waves(the primaries)reflected from subsurface reflectors but also the down-going waves(the ghosts)reflected from sea surface.The interference between the primaries and the following ghosts give rise to the waveform distortion of primary and the emergence of the false event,and this generates notches in the measured total wavefield spectrum.These notches reduce the usable measured signal bandwidth and affect the seismic data resolution,which bring difficulty to the inversion and interpretation of seismic data.A high-resolution and broadband seismic data is a prerequisite for the accurate imaging of complex geologic body.In order to achieve the goal,deghosting has to be performed during the process of seismic data processing.The undulating sea surface is one of the factors that can’t be neglected in the deghosting.However,single streamer(single component)deghosting algorithms that assume a flat surface will not account for the rough-sea surface.There may be inaccuracies in the estimate of the depth of each of the sensors and the reflection coefficient of the sea surface when considering the actual complex sea surface condition.This will lead to ghost residual and ringing artifacts in the deghosted output.In view of the above problems,the mechanism of ghost is first studied in this paper,then the theory and application condition of frequency-time domain,frequency-wavenumber domain and radon domain deghosting method are introduced,and the effect of the undulating sea surface on the deghosting result is analyzed.Finally,an adaptive deghosting method in frequency-time domain and a deghosting method in radon domain under the background of undulating sea surface are proposed,which can precisely suppress the ghost wave and provide technical support for deghosting.The frequency-domain adaptive deghosting method based on maximization of kurtosis evaluate the quality of deghosting result by defining the kurtosis coefficients,which can adaptively estimate the optimal ghost delay time to achieve the purpose of adaptive deghosting.The method can effectively suppress the ghost,and eliminate the notches caused by the ghost,and broaden the bandwidth of seismic data.The radon-domain deghosting method based on the sea surface imaging obtain the up-going wavefield at the sea surface by solving the least squares linear radon equation.The up-going wavefield are then extrapolated forward and backward to the receiver where a least-squares imaging condition is applied so that the shape of the sea surface can be estimated.The effect of the variable sea surface on the ghost can be taken into account by imaging the sea surface.The sea surface is then provided to the correction of the actual depth of the receiver.Finally,we compare receiver deghosting results using a flat sea surface and an undulating sea surface.Less ghost residual and reduced ringing artifacts are observed when deghosting was performed using an undulating sea surface.Test results on synthetic and field data show that the proposed approach can better remove ghost and achieve the goal of broadening the bandwidth of seismic data. |
