Richard O. Hansen & Alex Kaufman 
Principles of the Gravitational Method [PDF ebook] 

This self-contained monograph gives a thorough introduction to the theory of gravity which is used as the basis for developing applications in exploration and geodesy. In addition, a survey of gravity instrumentation is given, with emphasis on the theory of underlying these instruments. The book finishes with an exposition of forward modeling and inverston, again emphasizing fundamental principles.*Surveys gravity instrumentation with emphasis on the theory of why certain instrumentation is used*Presents thorough developments of the theory of gravity to aid in creating applications in exploration and geodesy*Emphasizes the fundamental principles of forward modeling and inversion in the gravitational method