Optical Engineering in Antarctica: Borehole Logging of Volcanic Eruptions and Ice Crystal Structure

Wednesday, November 16, 2016
6:00 AM to 7:00 AM
NHB 1.720
Free and open to the public

Two members of my research group deployed to Antarctica during two polar field seasons to make measurements of the volcanic signatures and crystal structures of deep glacier ice. This talk will cover what is involved for scientists to deployment to Antarctica and the scientific results we achieved with our instrumentation.

One of the most powerful methods for dating deep ice in the Polar Regions uses optical borehole logging, where an instrument is gradually lowered into a hole drilled into the ice and continually sends laser illumination out the side of the instrument. The laser light is scattered back from impurities in the ice, and the pattern of the scattered light versus depth gives critical information about the presence and timing of events such as ancient volcanic eruptions. A lightweight, high resolution, optical-fiber-based borehole logger was designed and constructed for measuring ash layers in shallow and intermediate depth boreholes. This logger weighed only a few pounds and could easily be fit in a backpack. We traveled to Siple Dome in Antarctica during the '13-'14 field season to test the instrument and analyze data from the logger, which measured the upper 300m of the Siple Dome borehole.

The logger turned out to provide the highest resolution optical logging ever performed. The physical reasons for the high resolution of this logger were two-fold. The logger was designed so that the ports of laser emission and detection were extremely close. In addition, the wavelength of the laser light source was chosen to be in the infrared so that the absorption length of the light in the ice was comparable to the scattering distance at the logging depths. This prevented dispersal of the light by scattering that would reduce the resolution of the logger. Most excitingly, this data was found to have extremely high correlations with chemically determined sulfate spikes in ice cores. This indicates that optical logging has the resolution necessary to isolate individual volcanic events. Looking forward, this will enable us to classify eruptions by tephra composition, conductivity, and particle shape, guiding glaciologists and volcanologists rapidly to the eruptions of global impact or other scientific interest and dramatically reduce the need to painstakingly chemically analyze core from uninteresting regions. 

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Joey Talghader

University of Minnesota Department of Electrical and Computer Engineering

Joseph Talghader obtained his B.S. in electrical engineering from Rice University in 1988. He was awarded an NSF Graduate Fellowship and studied at UC-Berkeley to obtain his M.S. and Ph.D. in 1993 and 1995, respectively, specializing in vertical-cavity lasers. During and after graduate school, he developed nonvolatile memory at Texas Instruments and Waferscale Integration. Dr. Talghader then joined the University of Minnesota, where he is now a Professor. His primary research areas are infrared detectors, optical coatings and materials, nanomechanical systems, and microsensors.