TEACHING GEOLOGY THROUGH PHYSICS: A REVIEW OF GEOLOGICAL IMAGING APPLICATIONS THROUGHOUT THE ELECTROMAGNETIC SPECTRUM

John Reid’s teaching brilliance in part stemmed from being a High School Physics instructor. John demonstrated that by bringing complex natural systems back to basic physics, many important problems can be resolved and the process of defining relevant hypotheses can be enhanced. He also demonstrated an ability to look at complex processes and reduce them into simplistic analogies as a means of providing the spark that ignites true scientific enquiry.

Geologic applications throughout the electromagnetic spectrum (EMS) include gamma ray spectrometry at very short wavelengths to RADAR at long wavelengths. The manner in which electromagnetic energy interacts with geologic materials and features is defined by wavelength, and by coherent or incoherent waveforms. Coherent radiation consists of a single wavelength such that a continuous relationship among phases is maintained allowing for tools such as diffraction and interferometry. The natural light detected with our eyes is incoherent as it consists of ranges of different wavelengths propagating in different directions. Color can be diagnostic of certain minerals and is used in spectroscopy whereby instruments can accurately measure the incoherent reflectance and absorption features that can be used to identify many minerals.

The Rayleigh criterion is taught to all undergraduate mineralogists as the basis for calculating crystal lattice spacings resulting from X-ray diffraction patterns. This simple trigonometric relation can also be applied to RADAR to resolve the sizes of geologic materials and can map surface texture related to lithology, yet this well known equation has rarely been used by RADAR geologists. Using digital terrain models the slope and aspect of a surface can be derived. Knowing the wavelength of the RADAR the sizes of the surface features can be determined by the amount of backscatter of the RADAR. These examples demonstrate how simple physics can help resolve geologic applications at different ends of the EMS and unite what are classically different disciplines within a broad range of geoscience applications.

Other examples will be provided to demonstrate how basic physics can provide an important key in resolving interdisciplinary geoscience problems. John Reid’s ability to do this well sparked a mode of enquiry in his students.