The majority of new and existing data have bandwidth limitations caused by free surface ghost reflections and the interference they cause.
The DUG Broad process results in a broadening of the spectrum as frequencies (both high and low) corrupted by the ghost wavefield are restored. This has a number of advantages for seismic interpretation through to quantitative inversion studies. The method is applicable to the processing of data from both the latest broadband acquisition systems and conventional (legacy) streamer data.
DUG Broad accurately formulates the forward ghost model using the wave equation in the f-p domain, fully incorporating arbitrary receiver and/or source depth profiles and a directional expression of stochastic free-surface reflectivity. The algorithm deals with azimuthal variability in 3D by assuming that the multi-streamer shot record has radial symmetry. To the extent that is fulfilled the algorithm is perfectly correct in 3D. This means that kinematically each trace is correct and the plane wave decomposition is locally accurate. Each streamer is treated independently. For each treamer, the Radon transform works in spatially overlapping windows. The transform fully handles variable trace spacing. The radial symmetry assumption is imposed by using the Euclidean distances between source and receiver, rather than distance of arc along the streamer as the space variable in the Radon transform. Azimuthal binning is not performed. However, by using space windowing and a radial symmetry assumption, different source receiver azimuths are deghosted separately. The forward model is expressed as the system of equations, Gu=d.
Given the observed data, d(x), and the forward ghost modelling operator, G(p,x), we solve for the up-coming wavefield, u(p), at the free-surface for each frequency. The system is solved in a least squares sense using robust conjugate gradient methods. DUG Broad accurately deghosts all events, offsets and dips. The algorithm has no dependency on the earth model, other than knowledge of the water velocity. Benefits include robust and stable deghosting behaviour and the availability of output data referenced to the free-surface for all subsequent processes such as SRME, velocity analysis and migration.
Deep water, slant cable shot record before and after source and receiver deghosting using DUG Broad.
Stack section before and after application of DUG Broad. Both source and receiver deghosting has been applied. This data was acquired with a 15 m flat cable in a shallow water setting.