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Fig. 14. Mean dominant period as a function of explosion height. This shows
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increasing period with height, as pointed out earlier by Herrin et al.
across the multiple explosions. Beginning at about 100 km dis- tance, the waveforms for explosions separated by only four hours in time showed significant variations due to atmospheric effects.
The data collected during the WSMR experiments, com- bined with the precise data on the six explosions, are proving to be of significant value across the entire spectrum of infra- sound research, including source studies, propagation, instru- mentation and data processing. Focused analyses using the WSMR data to answer questions both fundamental and prac- tical are underway. For example, the WSMR data will fuel studies of a broad suite of processing algorithms to gauge the relative utility of each approach for detecting and characteriz- ing signals. Furthermore, there are a number of important questions in propagation modeling to be investigated: Can accurate model attenuation and accurate absolute, or at least relative, signal amplitudes be predicted? In doing so, can it be predicted which stations should be able to record signals above the noise? How accurately can the timing of the arrivals at each station be predicted? Is the azimuth bias due to crosswinds accurately predicted? Can multipathing be predicted, or the overall waveform structure at each station? Do predictions improve noticeably with up-to-date atmospheric specifica- tions? Comparisons between the predictions and the observa- tions will provide a means to quantify the performance of the existing models, identify deficiencies in the models where physical processes may not be accounted for, and ultimately expand understanding of the interaction between propagating sound waves and atmospheric dynamics. The data are also being used to test advanced instrumentation concepts, includ- ing optical fiber infrasound sensors and the distributed sensor.
Progress in these areas, however, should also improve the ability to use infrasound data to monitor the atmosphere and the shallow earth for nuclear explosions. In this arena, event detection, location and identification are key issues. The WSMR data will be used to determine if waveform record- ings can be used to identify unambiguously the source as an explosion, and to determine accurately both the geographic position of the source and its altitude. The experiments used an unusually high density of infrasound sensors, and thus there is a rare opportunity to assess the station density required to obtain sufficiently accurate location estimates and learn more about the range from which useful informa-
tion about the source can be extracted.
In summary, the WSMR experiments will foster basic
research as well as provide further insights relevant to nuclear monitoring in addition to proving useful in testing the use of infrasound data for monitoring natural hazards.
Participants
In addition to the authors of this article, the following people participated in various aspects of the WSMR experi- ments:
C. Talmadge, C. Hetzer, S. Breeding, R. Stribling, S. Dravida, V. Male, The University of Mississippi;
D. Fee, W. Bortz, The University of Hawaii;
J. Heberly, Army Research, Development and Engineering Center;
C. Coon, E. Blum, M. Zumberge, R. Matoza, P. Walsh, P. Durdevic, J. Berger, S. De Wolf, The University of California, San Diego;
P. Negraru, Southern Methodist University;
H. Israelsson, M. Bahavar, B. North, Science Applications International Corporation;
S. Mangino, Department of Defense Nuclear Treaty Managers Office;
J. Noble, Army Research Laboratory;
R. Gibson, J. Bhattacharyya, BBN Technologies;
D. Osborne, J. Olson, J. Helmericks, The University of Alaska Fairbanks;
K. Dillion, J. Williams, A. Kent, T. Turner, Miltec Corporation;
M. McKenna, U.S. Army Engineering Research and Development Center;
K. Veith, ITT Corporation;
J. Behrens, R. Wright, BAI, Inc.
Financial support was provided by the U. S. Army Space and Missile Defense Command.AT
References for further reading:
1 E. Herrin, P. Golden, P. Negraru, H. Bass, G. Hunter, W. Andre, J. Olson, D. Osborne, M. Garcés, M. Hedlin, and K. Hoffmann, “Infrasound calibration experiments at White Sands Missile Range: Planning and Preparations,” Proceedings of the 26th Seismic Research Review, LA-UR-01-5801, 645-653 (2004).
2 B. Andre, “Infrasound Rocket Experiment,” InfraMatics 12, 1-3 (2005).
3 B. Andre and H. Bass, “High-altitude infrasound propagation experiment,” J. Acoust. Soc. Am. 120, 3031 (2006).
4 M. S. O’Brien, D. P. Drob, and J. R. Bowman, “Improved Infrasound Event Location,” Proceedings of the 29th Seismic Research Review, LA-UR-07-5613, 874–883 (2007).
5 S. N. Kulichkov, “Long-range propagation and scattering of low frequency sound pulses in the middle atmosphere,” Meteorology and Atmospheric Physics 85, 47–60 (2004).
6 V. E. Ostashev, I. P. Chunchuzov, and D. K. Wilson, “Sound prop- agation through and scattering by internal gravity waves in a sta-
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