Inverting Waveforms for Velocities in the Presence of Caustics
نویسندگان
چکیده
Transmission caustics cause velocity estimation techniques based based on straightforward analysis of image volume moveout to fail. For example the diierential semblance objective function (a quantitative measure of image volume moveout) is smooth and has only kinemat-ically correct critical points when the incident waveeeld is free of caustics, but loses these properties when caustics are present. The reasons for this phenomenon are closely related to those identiied by Geoltrain and Brac for the inadequacy of Kirchhoo migration based on rst arrival times for complex velocity structure. Controlled illumination of the subsurface, introduced by Rietvold and Berkhout to improve imaging given an adequate macromodel, also suggests a new approach to image volume moveout analysis for macromodel estimation. The transmission inversion (crosswell tomography) problem provides a simple framework within which to illustrate the controlled illumination reformulation of diierential semblance and its eeectiveness.
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