Comparison of unstacked inline results

Using CAM as the imaging operator in my least-squares inversion means that my geophysical regularization operator will only be acting along the inline p_h axis. Therefore, the most significant changes between the CAM result and the geophysical RIP result will be seen in unstacked results. To study these, I have selected several unstacked inline volumes from crossline=20.9 km. These volumes can be seen in Figures  through , where (if you rotate the pages 90^o clockwise) I am displaying the depth slice on the top of the figure, the common inline p_h section on the left, and the common image gather to the right of the common inline p_h section. The migration result is shown first, then the geophysical RIP result for each (common inline p_h section - common image gather) pair.

Figures  and show a common inline p_h section from p_h=.1875 and a common image gather from inline position 20.375 km. Comparing Figure  and Figure , the RIP result is considerably cleaner. The effects of the regularization are clear in the common image gather (right part of the figures), where the unlabeled oval indicates gaps in the events that are filled by RIP. In the common inline p_h section, the ovals indicate particular areas of the shadow zones that are being filled in. Oval ``A'' highlights a reflector that is discontinuous and has inconsistent amplitudes where it does exist in the migration result. In the RIP result, this reflector is continuous with strong amplitudes along its full extent. Oval ``B'' extends across one of the shadow zones. The shadow zone is considerably cleaner in the RIP result, with almost none of the up-sweeping artifacts seen in the migration result. Also, the reflectors themselves extend farther into the shadow zone, particularly on the right side of the oval. The events also extend farther into the shadow zone indicated by oval ``C''.

Moving further under the salt and to a larger offset ray parameter, Figures  and show a common inline p_h section from p_h=.2325 and a common image gather from inline position 21.65 km. The unlabeled oval in the common image gather shows events that have been strengthen and are more horizontal in the RIP result (Fig. ) than the migration result (Fig. ). The ovals marked ``A'', ``B'', and ``C'' on the common p<sub>h</sub> sections show the same type of improvement seen in the previous comparison (Figs.  and ). The reflectors at the right side of oval ``B'' in Figure  extend much farther into the shadow zone than those from the migration result.

Another interesting comparison can be made at common inline p_h section from p_h=.15 and a common image gather from inline position 20.9 km (Figures  and ). In this migration result (Fig. ), the common image gather once again has events with gaps caused by poor illumination, indicated by the unlabeled oval. These gaps are largely filled by 7 iterations of RIP, as seen in Figure . We see the same improvements in ovals ``A'', ``B'', and ``C'' as discussed for the previous two comparisons. In this comparison, there is an additional oval ``D'' that indicated reflectors under the salt that are less affected by artifacts and more likely to be accurate in the RIP result than in the migration result.

Finally, looking at the same common image gather from inline position 20.9 km but moving the common inline p_h section to p_h=.2925, we compare Figures  and . In this common p_h section, the effect of the critical angle and user-defined mutes described in the previous chapter can be seen in and below the salt body. The oval in the common image gather shows the same events with gaps in the migration result (Fig. ) that are filled by RIP (Fig. ) that was seen in the previous comparison. It is interesting to see that the improvements seen in the ``A'', ``B'', and ``C'' ovals in the previous examples are also seen in this example, at a much larger p_h. RIP has a positive effect for a large range of p_h.

 

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Figure 18 Migration result. Crossline=20.9 km, common inline p_h section from p_h=.1875, and common image gather from inline=20.375 km. Compare with Figure .

 

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Figure 19 Geophysical RIP result. Crossline=20.9 km, common inline p_h section from p_h=.1875, and common image gather from inline=20.375 km. Compare with Figure .

 

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Figure 20 Migration result. Crossline=20.9 km, common inline p_h section from p_h=.2325, and common image gather from inline=21.65 km. Compare with Figure .

 

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Figure 21 Geophysical RIP result. Crossline=20.9 km, common inline p_h section from p_h=.2325, and common image gather from inline=21.65 km. Compare with Figure .

 

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Figure 22 Migration result. Crossline=20.9 km, common inline p_h section from p_h=.15, and common image gather from inline=20.9 km. Compare with Figure .

 

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Figure 23 Geophysical RIP result. Crossline=20.9 km, common inline p_h section from p_h=.15, and common image gather from inline= 20.9 km. Compare with Figure .

 

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Figure 24 Migration result. Crossline=20.9 km, common inline p_h section from p_h=.2925, and common image gather from inline=20.9 km. Compare with Figure .

 

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Figure 25 Geophysical RIP result. Crossline=20.9 km, common inline p_h section from p_h=.2925, and common image gather from inline=20.9 km. Compare with Figure .