Acoustic Tomography in Boreholes Using an Algebraic Reconstruction Technique.
COLORADO SCHOOL OF MINES GOLDEN CENTER FOR WAVE PHENOMENA
Pagination or Media Count:
An algebraic reconstruction technique ART is described for the seismic tomography of velocities from the travel times of a multiple offset vertical seismic profile. ART concentrates on the production of a reconstructed field whose projected data travel times agree with the observed data. This reconstructed field is modified by altering the data for each ray such that when this data is back-projected, the new image agrees with the original data. Because the paths of the rays must be known to calculate the expected travel times, the problem is linearized by using raypath approximations as determined from either a constant or a linear cz velocity medium. Imaging of synthetic data revealed that the orientation of the anomaly affects both the rate of convergence and the resolution of the reconstructed field. Some smoothing of the velocity anomalies occurred along the direction of the rays. Noisy data sets developed problems in the reconstructed velocity field. Huge single point anomalies appeared along the models edge in the reconstructed image.