This example shows the processing sequency applied to Vertical Seismic Profile (Gaz de France) data. In initial data, upgoing waves appear in the f,k domain with negative wavenumbers and downgoing waves with positive wavenumbers. The different steps of the processing are presented in domains t,x and f,k:

• Downgoing waves velocity correction: Delays used to realize this flattening have been obtained by crosscorrelation of different traces of the VSP with the first trace;
• Downgoing waves selection: The downgoing wavefield is obtained by a serie of 3 median filters applied successively on the offset axis to flattened data. The number of respective terms of the median filters is 3, 5, and 7.The residual wavefield is the difference between initial flattened data and donwgoing wavefield;
• Delays correction applied to the residual wavefield to flatten the upgoing wavefield by using downgoing waves velocity;
• Upgoing waves selection: The application of a median filter on the residual wavefield is used to extract the upgoing wavefield. This processing improves the visibility of these waves but does not notably modify the stack presented below;
• Deconvolution: Deconvolution of upgoing waves by downgoing waves is done trace by trace. This operation is obtained by spectral division. In order to limit an over-amplification of noise, we will choose the regularisation constant. The application of a median filter on the upgoing deconvoluted wavefield improves the visibility of reflectors but does not notably modify the stack shown below;
• Corridor stack: Deconvolved and horizontalized upgoing waves are stacked in a corridor immediately following the first arrival. The result is a stack directly comparable to multifold seismic sections. The figure “stack” allows a comparison of stacks associated to upgoing waves (extracted with or without application of a median filter) obtained before and after deconvolution.