The need for subsurface information: The motivation for using geophysics

Non invasive imaging

As mentioned in the previous section geophysical imaging and medical imaging are both noninvasive approaches. These methods share key attributes and explore the same physics and mathematics, and suffer from similar limitations. We use the general knowledge that most everyone has about medical imaging to introduce the key attributes of non invasive imaging.

In medical imaging an instrument is used to answer a question about what is happening inside a body. Different instruments are used (X ray, ultrasound, MRI), and data is obtained from that instrument. The instrument which is used depends on the question which is asked: to get an answer to question on teeth one uses an X-ray, to get an answer on questions about the progress of pregnancies one uses ultrasound. The instrument creates an image, which is interpreted by a specialist to answer the original question.

Noninvasive imaging This description provides us with the key attributes of non invasive imaging which apply equally to geophysical and medical imaging:

  • An instrument is used "from the outside" to answer a question on some condition "on the inside"
  • Different instruments are used to answer different questions
  • The instrument generates an image
  • The image is interpreted by a specialist to answer the original question

Keeping these attributes in mind should help the non geophysicist to develop an initial understanding of what geophysical imaging is. Of course, there are several questions which are raised by this description of key attributes. Specifically, these are

  • what exactly is this image which is generated by the instrument?
  • how does this image get generated?
  • why do we need different instruments?
  • how is an image interpreted so as to give an answer to the original question?
While a comprehensive answer to these questions will require the reader to dive into geophysical (or medical) literature, in the section on Geophysical Imaging some answers to these questions are provided. These questions should increase the general understanding of geophysical imaging (and what geophysical imaging can and cannot do).