Geophysics is the science of applying the principles of physics to investigations related to the structure and properties of the earth. It has been said that geophysics essentially is the measurement of contrasts in the physical properties of materials beneath the surface of the earth and an attempt to deduce the nature and distribution of the materials responsible for these observations. Geophysical exploration has been utilized in numerous fields to study a wide range of targets within the earth from discovering the deep structure of the earth at thousands of meters to near surface structures and properties at depths of a few tens of meters. Some of the latest geophysical technologies are targeted at studying engineered material, such as pavements and bridge decks at only a few centimeters depth. Geophysical surveys are conducted on the ground surface, within drill holes, and from the water and air. A partial list of applications includes: mineral and petroleum exploration and production, environmental contaminant mapping, mapping subsurface ground conditions for civil engineering projects, solution cavity detection, hydrological mapping, mapping near surface utilities, detection and mapping of unexploded ordnance, and archeological and forensic investigations.