Description of the Synthetic Data

The velocity model used to generate the synthetic data is shown in Figure . The water bottom is deep, flat on the inline direction and dipping at 15 degrees in the crossline direction. The only reflector is a plane dipping 3 degrees in the inline direction and 15 degrees in the crossline direction.

 

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Figure 1 3-D velocity model.

The geometry of acquisition consists of 10 receiver lines, each with 240 receivers spaced 25 m, with the first receiver at an inline offset of 100 m from the source. The maximum inline offset is therefore 6075 m. The receiver line separation is 100 m and the source is dual flip-flop with the two sources separated 50 m in the crossline direction and centered between the two middle streamers with a 25 m crossline distance from the closest streamer. There are a total of 6 sail lines with each sail line separated from the next by a crossline distance of 450 m. With this arrangement, the crossline fold is just one and the fold in the inline direction is 60. Figure  shows a schematic of two adjacent sail lines illustrating that there is no overlap between the CMP coverage of each sail line. Figure  shows the receiver map, the source map, the azimuth-offset distribution and the fold map, all typical of a dual source flip-flop acquisition.

 

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Figure 2 Schematic of fold coverage of two adjacent sail lines.

 

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Figure 3 Top left: receiver map. Top right: source map. Bottom left: azimuth-offset distribution. Bottom right: fold map.

Figure  shows a typical source record. The 10 receiver lines are clearly seen. There are four reflections: the water-bottom primary, the deeper reflector primary, the water-bottom multiple and the peg-leg reflection between the water-bottom and the deeper reflection. Notice the change in polarity of the multiples as compared to the primaries. Figure  shows a close up of the wavelet and the wavelet spectrum which shows that the wavelet has a DC component.

 

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Figure 4 A typical ``shot'' gather showing the 10 receiver lines. Notice the polarity inversion of the multiples.

 

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Figure 5 Close up of the seismic wavelet (a) and its frequency spectrum (b). Notice the uncharacteristic low frequencies.