Pulse time-delay method for geophysical tomography

Geotomography methods are presented for reconstructions of index-of-refraction distributions for time-delay measurements. Two versions of the algebraic reconstruction technique (ART) are compared to the conjugate residual (CR) method with Lagrange multiplier conditioning. The CR method with Lagrange multiplier conditioning provided the best reconstructions for good anomaly boundary definition under noisy conditions. A ray bending model to account for refraction is also used in the reconstructions. Modifications are made in the algorithm to simplify its use and to improve the convergence stability. Two image filters, the two-group minimum-variance partition-average (MVP2-AVE) one and the selective smoothing (SS) one, are used in succession and some of the limitations of each filter are eliminated. This improves the implementation of the filters and the accuracy of the reconstructions