Dec. 23, 2011: "Acoustic Ray Tracer, 2D" or "ART2D" has been released. Check out the link here.

Dec. 13, 2011: My USArray work has been published. Many thanks to JGR Solid Earth and two anonymous reviewers for helping this go to press so quickly. Click here for the paper.

Jan. 13, 2011: UCSD infrasound arrays are detecting microbaroms coming from the eastern Pacific Ocean. CLICK HERE FOR AN OCTOBER 2011 UPDATE or HERE FOR A JANUARY 2012 UPDATE. Each of the arrays comprise several infrasonic microphones separated by several hundred meters. Pressure signals generated just above the ocean surface, likely from beating due to interfering opposing swells, travel great distances through the atmosphere. These signals are detected by each of the sensors in the arrays. Array processing identifies the direction from which the signals originated (back azimuth). We project these back azimuths outward from these arrays to form an intersecting back azimuth density color map, where reds indicate high densities. The color map has been converted to signal-to-noise ratio. The black contour is the statistical 95% confidence region for a model where there is only one source to explain all the detections at the arrays. The OFIS CHIAR array provided results that were consistent with those of the other arrays. This is the first time that the OFIS technology has been used for infrasound source physics research. Click here for a movie.

Geophysics Project Scientist
Inst. of Geophysics and Planetary Physics
Scripps Institution of Oceanography
University of California, San Diego

Contact info

Research Summary

The study of subaudible sound (called infrasonics) is an exciting new field with many problems to solve. I have been conducting research in several areas of infrasonics during the last few years as a member of the Gravity Lab and the Laboratory for Atmospheric Acoustics. These areas include infrasonic source imaging, earthquake infrasound, wind noise reduction, sensor design, and array processing techniques. I have recently begun a project in the imaging of microbarom/microseism source areas. I have also been working on assessing the degree to which very large earthquakes radiate global and regional infrasound. Lastly I have been constructing the Southern California Infrasonic Array Network (SCIAN) to build a local research infrastructure, as well as assembling archives of global infrasound array data, U.S. west coast infrasound array data, and 4-D atmospheric acoustic velocity models. Click here for more information.

Curriculum Vitae [PDF]

Education

2004: Stanford University, Ph.D., Passive-source Seismology (Thesis)
2000: Stanford University – M.S., Active-source Seismology
1998: University of Delaware – B.S. w/ Distinction, Geophysics, Cum Laude

Professional Experience

• 2010-11: Lead PI, Chico Microbarom Source Physics Experiment (OFIS array deployment and research)
• 2010-11: PI, Santa Margarita Microbarom Source Physics Experiment (SMIAR MB2000 array deployment and research)
• 2009: Lead PI, Evaluation of Line Averaging as a Means of Wind Noise Reduction (270 m long OFIS at Piñon Flat Observatory)
• 2009-11: Project Scientist, IGPP, Scripps, Univ. of California, San Diego
• 2007-08: Co-PI, six-element infrasound array "MRIAR" near San Diego, California
• 2005-06: Cecil & Ida Green Scholar, IGPP, Scripps, Univ. of California, San Diego
• 2004-09: Postdoctoral Researcher, IGPP, Scripps, Univ. of California, San Diego
• 2000-01: Lead Investigator, Snake River Plain Seismic Experiment
• 1998: Participant, Summer of Applied Geophysical Experience program

Recent Publications

Walker, K.T., Shelby, R., Hedlin, M., de Groot-Hedlin, C., and Vernon, F., 2011, Western U.S. Infrasonic Catalog: Illuminating infrasonic hot spots with the USArray, J. Geophys. Res., 116, B12305, doi:10.1029/2011JB008579.

de Groot-Hedlin, C., Hedlin, M., and Walker, K., 2011, Finite difference synthesis of infrasound propagation through a windy, viscous atmosphere: application to a bolide explosion detected by seismic networks, Geophys. J. Int., doi: 10.1111/j.1365-246X.2010.04925.x

Walker, K.T., Hedlin, M.A.H., de Groot-Hedlin, C., Vergoz, J., Le Pichon, A., and Drob, D.P., 2010, Source location of the 19 February 2008 Oregon bolide using seismic networks and infrasound arrays, J. Geophys. Res., 115, B12329, doi:10.1029/2010JB007863.

Hedlin, M.A.H., D. Drob, K.T. Walker, and C. de Groot-Hedlin, 2010, A study of acoustic propagation from a large bolide in the atmosphere with a dense seismic network, J. Geophys. Res., 115, B11312, doi:10.1029/2010JB007669.

Walker, K.T., and Hedlin, M.A.H., 2010, A review of wind noise reduction methodologies, in: Infrasound Monitoring for Atmospheric Studies, ed. by A. Le Pichon, E. Blanc, and A. Hauchecorne, Springer, p. 141-182, doi:10.1007/978-1-4020-9508-5.

Walker, K.T., and Shearer, P., 2009, Illuminating the near-sonic rupture velocities of the intracontinental Kokoxili Mw 7.8 and Denali Mw 7.9 strike-slip earthquakes with global P-wave back projection imaging, J. Geophys. Res., 114, B02304, doi:10.1029/2008JB005738.

Walker, K.T., Zumberge, M.A., Hedlin, M.A.H., and Shearer, P., 2008, Methods for determining infrasound phase velocity direction with an array of line sensors, J. Acoust. Soc. Am., 124, 2090-2099.

De-Groot Hedlin, C.D., Hedlin, M.A.H., Walker, K.T., Drob, D.P., and Zumberge, M.A., 2008, Study of infrasound propagation from the Shuttle Atlantis using a large seismic network, J. Acoust. Soc. Am., 123, 3829-3829.