The shallow subsurface of the earth is vital to the well being of humankind. It is the source of many of our resources and of ground water. Where we excavate from the earth, how we build on it, and where we dispose of waste in it are of increasing concern as the global population grows. The associated need to locate objects or geological structures in the shallow subsurface in a noninvasive way is a challenge that is being met by geophysics, which has provided a range of geophysical methods and instruments suited for this purpose. One of the most successful...

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