ABSTRACT
Since the early part of the last century, geophysical techniques have been used to probe the Earth's interior. Because of the obvious economic incentives, a great deal of this effort was focused on resource exploration. Also dating back to the early part of the last century is a mathematical relationship known as the Radon transform. It has long been known that this transform could serve as the basis for tomographic imaging. However, it was not until the 1970s that computing power reached a level sufficient for implementation of the Radon transform in imaging. The first use of the Radon transform in tomographic imaging was CT scanners used in diagnostic medicine. These devices use x-rays and reconstruct images by backprojection. These rays will travel in straight lines in organic materials such as the human body and, as such, imaging by backprojection is valid for these applications. The Radon transform provides images comparable to those that can be obtained by the backprojection process described in Sect. 11.4. However, the application of imaging by this transform is far more computationally efficient, particularly in situations where a large number of source and receiver positions are used. The success of the CT scanner stimulated development of new imaging techniques and applications in many disciplines, including geophysics.
