Modeling of the multiples

In the shot domain, for one frequency, the multiple model is given by the spatial non-stationary convolution of shot gathers Dragoset and Jericevic (1998); Verschuur et al. (1992). The synthetic model has an offset spacing of 12.5 m and a shot separation of 50 m. To make the multiple prediction work, the offset axis is sampled down to 50 m. Figure 1 shows one constant offset section from -15,000 m to +15,000 m.

This section of the dataset is particularly interesting because of the diffractions visible throughout. Because no velocity model or sedimentary section is available, a possible interpretation of these diffractions is the presence of salt bodies with a rugose top (similar to what we see with the Sigsbee2B dataset). The multiple model is shown in Figure 2 for the same offset. DT points to diffraction tails where the model is not properly rendering the multiples in the data. Besides these few imperfections in the model, the model looks very faithful to the actual multiples. The pattern recognition technique and the adaptive subtraction are compared in the following section.

 

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Figure 1 Constant offset section (h=500 m) of the data with multiples. DTs point to the tails of diffracted multiples.

 

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Figure 2 Constant offset section (h=550 m) of the estimated multiples. The multiples are accurately modeled except for the diffracted multiples, shown as DT, for which the limited range of offsets and number of shots hamper any attempt at modeling the diffraction tails.