A study of the effects of transducer size on physical modeling experimentsfor recovering anisotropic elastic parameters

The effect of finite size transducers on elastic parameters recovered from laboratory measurements has been studied in this paper. Ultrasonic transmis sion experiments in the physical modeling laboratory were used to acquire t he first arrival traveltime data at different ray angles, to simulate walka way VSP surveys in the field. The elastic parameters of the materials were then recovered by our developed inversion techniques, using velocities at d ifferent directions inverted from the first arrival traveltimes. In our lab oratory experiments, "point" transducers and "large" transducers were used to carry out the transmission experiments. The finite size of the transduce rs introduced systematic errors in the first break picks along the survey l ine, and hence the determined velocity field was inaccurate. These systemat ic errors cannot be corrected by the inversion technique. Numerical simulat ions were also conducted to study the differences between experiments using large and point transducers. From our experimental measurements, accurate elastic parameter values are obtained when the ratio of the sample-thicknes s to transducer-diameter is greater than 36. Decreasing the size of the tra nsducers is highly recommended when conducting laboratory experiments to re cover elastic parameters. A method of offset correction is also implemented in an attempt to decrease the measurement errors.