After building the first government mobile ground magnetometer and traversing tens of thousands of miles taking magnetic data, I had a natural thesis topic–interpreting some of the data.
I chose a small section of traverse in northeastern Minnesota, where lava flows lie in horizontal layering.
To make it unique, I used the variable magnetic properties in the flows to determine the depth of a highly magnetic layer overlain by a less magnetic layer. To do this I analyzed the rock magnetism that the seemingly erratic magnetic field traverse exhibited.
To analyze the traverse data I used Fourier (wavelength) analysis. To convert the traverse data from a line on chart paper to wavelength form I developed an electro-optical converter using an oscilloscope and camera.
(I know this is getting boring. If you want to know more, read my Master’s Thesis. I have two copies.)
Using this unique and clumsy system I was able to show that a less magnetic layer (rhyolite) is about 70 feet thick at the traverse location, and overlies a more magnetic (gabbro) layer. The test also gave some indication of the magnetic inhomogeneity of both layers.
At Prof. Mooney’s request I sent a short description of the technique and my results to Isidore Zietz, a geophysicist and magnetic expert with the US Geological Survey in Washington, DC. Dr. Zietz replied that it appeared to be a Ph.D. level thesis. He passed my letter on to James Balsley, head of USGS geophysics branch. The letter to me from Dr. Zietz contained a handwritten note from Dr. Balsley in support, with recommendations for further work.
Being more interested in field exploration at the time, I did not follow up on Dr. Balsley’s suggestions.