One difficulty in applying seismic tomography is that seismic sources and detectors cannot be deployed so that the imaging area is probed from all directions. This paper develops two methods to alleviate this difficulty. These methods combine the minimum cross entropy estimation algorithm with two tomographic image reconstruction algorithms: the direct transform reconstruction algorithm and the backpropagation reconstruction algorithm. These two methods were tested by numerical and scaled model ultrasonic laboratory experiments simulating seismic cross‐hole tomography. It was found that (1) the horizontal resolution, which is inherently poor for the cross‐hole geometry, can be improved, and (2) artifacts caused by the sparse sampling and noise can be reduced. Both methods work better when the targets are isolated impulses surrounded by a uniform background medium.

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