A cross-hole ray tomography system is designed for imaging strongly varying velocity distributions; key features are ray bending and the incorporation of multiple raytraces to update the ray paths as the velocity estimates converge. In this context, convergence means that time residuals are stationary both between tomography iterations and between raytraces.

For strongly variable velocities, simultaneous iterative reconstruction is recommended rather than classical algebraic reconstruction (convergence is slower but stability is improved). Picking of arrival times must be very sophisticated and involve many arrivals if structural details are to be resolved. Examples include both synthetic and scale model data.

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