Scaling
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This section describes various approaches to scaling data. These include both deterministic and statistical scaling routines, as well as specific application such as surface consistent scaling and acquisition footprint suppression.
Standard marine processing sequences are designed to be controlled-amplitude, controlled-phase (CACP), in which only deterministic scaling would normally be applied. Typically spherical diverge is applied for the pre-processing and then removed before imaging, as the migration programs can apply a more accurate ray-traced divergence correction. Acquisition footprint corrections (shot and channel scalars and de-striping) would also be applied.
Q guided wavelet domain de-absorption: QWAVE
QWAVE applies a frequency-dependent, space and time varying, amplitude absorption correction. A relative correction to an estimated background trend is computed and applied. The analysis and correction is performed in the wavelet transform domain as this has the feature of resolution in both time and frequency and provides the ideal domain in which to analyse time and spatial variations in the frequency content of data. The frequency-dependent scalars are computed using the spectral ratio method for Q estimation. This process is an established method for estimating Q from seismic data but is subject to various instabilities and inaccuracies with respect to the final absolute Q measurement. In QWAVE relative variations in the attenuation with respect to a background trend are estimated. Analysis of the log spectral ratios as a function of frequency provides estimates of relative attenuation variations that are then used to compute the frequency-dependent scalars. The relative Q variations also provide an attribute that is potentially useful for interpretation.
Surface Consistent Scaling: SCAVE
Surface consistent scaling decomposes the amplitude variations in data into shot, receiver, CMP and offset consistent terms in a least-squares sense using an iterative Gauss-Seidel algorithm and computes scalars to correct for a subset of these terms that are then applied to the data. Typically shot, receiver, CMP and offset terms will be derived but only shot and receiver corrections applied. The analysis is able to handle data from different instruments (e.g. geophone and hydrophone, or dynamite, vibroseis and air-gun) at the same surface locations.
Acquisition Footprint Compensation: De-striping
Residual acquisition footprint corrections analyse the time-varying amplitude behaviour within common offsets for acquisition related amplitude striping in the shooting direction. This is used to derive time-varying correction scalars that can then be applied to the pre-stack data. This type of correction is applied to the data before migration if acquisition footprint variations can still be observed after standard shot-channel amplitude corrections