PRACTICAL IMPLEMENTATION OF AVALANCHE INFRASOUND MONITORING TECHNOLOGY FOR OPERATIONAL UTILIZATION NEAR TETON PASS WYOMING Ernest D. Scott* Inter-Mountain Laboratories, Inc., Sheridan, WY Christopher T. Hayward Southern Methodist University Department of Geological Sciences, Dallas, TX Timothy J. Colgan, Jerry C. Hamann, Robert F. Kubichek, John W. Pierre University of Wyoming Department of Electrical and Computer Engineering, Laramie, WY Jamie Yount Wyoming Department of Transportation, Jackson, WY ABSTRACT: Recent advancements in infrasound monitoring hardware and software for the detection and identification of avalanche-generated infrasound signals have resulted in operation of a prototype monitoring system targeting avalanche activity occurring in the problematic slide paths that impact Wyoming State Highway 22 near Teton Pass. Implementation of the technology was facilitated in a manner aimed at providing a practical operational tool for the Wyoming Department of Transportation’s avalanche hazard mitigation program. Custom sensors coupled with novel array processing have exhibited robust performance to the deafening and detrimental affects of ambient wind noise. Occurrences of false positive identification of interfering infrasound signals as significant avalanche events have been virtually eliminated through data processing discrimination methods that are based on source location features of detected signals. Performance of the automated signal discrimination methods decrease with respect to small avalanche events that do not travel far, but small events are still recognizable in system results by a skilled human interpreter. A remaining challenge is to improve the reliability of the infrasound signal path between the atmosphere and the sensor, which is covered by a variable snow pack. Upon resolving signal path issues, the technology will have reached a mature and stable state that can easily be utilized by the avalanche practitioner in appropriate applications without the need for continued extensive research and development activities. KEYWORDS: Avalanche monitoring, infrasound, signal discrimination, sensor array 1. INTRODUCTION Many past research studies have shown that snow avalanches generate acoustic signals within a low noise band of the sub-audible infrasonic frequency spectrum (Bedard 1989, Bedard 1994, Bedard et al. 1988, Chritin, et.al. 1996, Scott and Lance 2002, Comey and Mendenhall, 2004). These low frequency infrasound signals have the ability to propagate kilometers from the avalanche source and provide a basis for developing wide area automated monitoring systems that can operate in locations unaffected by avalanche activity. Such avalanche monitoring systems hold the potential to provide valuable information for professionals charged with responsibilities related to avalanche activity. Especially useful is the ability of an infrasound _____________________________________ *Ernie Scott, Inter-Mountain Laboratories, Inc., Sheridan, WY 82801; tel: 307-674-7506; fax: 307- 672-9845; e-mail: escott@imlinc.com avalanche monitoring system to compliment and verify results of avalanche hazard mitigation efforts. 2. STUDY BACKGROUND Since investigations of infrasound sensor array signal processing capabilities conducted during the 2003/2004 winter season produced encouraging results (Scott et al. 2004), prototype near real-time infrasound sensor array avalanche monitoring systems were operated in close proximity to Teton Pass, Wyoming during the 2004/2005 and 2005/2006 winter seasons. These prototype monitoring systems were operated with the intent of providing the Wyoming Department of Transportation (WYDOT) with an informational tool to support their avalanche hazard mitigation program for Wyoming State Highway 22. 714