Infrasound Signals from Repeating Detonations at the Utah Test and Training Range Recorded in North America J. Roger Bowman and Gordon Shields Science Applications International Corporation Presented at the Infrasound Technology Workshop Bermuda November 3-7, 2008 Approved for public release; distribution unlimited DISCLAIMER “The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either express or implied, of the U.S. Army Space and Missile Defense Command or the U.S. Government.”

2 Introduction  Objective  Detonations  Infrasound data  Observations  Modeling  Conclusions

3 Objective  Explore seasonal variation of infrasound propagation on a variety of paths

4 Utah Test and Training Range  ICBM motors are regularly disposed of by detonation at the Utah Test and Training Range (UTTR) west of Salt Lake City, Utah  Yields: t of a missile motor at the UTTR Open burn/open detonation of a missile motor at the UTTR Launch of a Poseidon missile, one type being disposed of at UTTR since 1995

5 Detonation Distribution  148 explosions in 4+ “years” Origin times from seismic data kindly provided by Relu Burlacu at the University of Utah

6 Infrasound Data June 22, 2004 at 17:12:29 Observed primarily at stations west of UTTR April 12, 2004 at 20:59:00 Observed primarily at stations east of UTTR We analyzed waveforms from all infrasound arrays in North America for all 148 detonations

7 Infrasound Signal Analysis Multiple (3-8), discrete arrivals are a key feature of signals from UTTR detonations Attributes are measured separately for each arrival

8 Detection of Detonations Detected Not Detected No Data Signals detected to the west in the “summer” Signals detected to the east in the “non-summer” Signals detected at all stations except TXIAR (I59US not in operation) Signals detected at PDIAR in “all seasons” (but lower coherence in “summer”) Signals detected for 138 of 148 detonations

9 Seasonal Variation in Celerity: The Best Each of 4 or 5 arrival sets makes an arcuate pattern with day of year, with maximum celerity mid-summer Seasonal pattern is similar from year to year Arrivals are color coded by sequence number (gray when not part of the normal sequence).

10 Seasonal Variation in Celerity : The Rest Consistent with arcuate pattern at other stations to the west, but no clearly defined sequence of arrivals Three arrivals don’t make a pattern! As many as 8 arrivals per sequence Slower, less coherent arrivals in the summer

11 Seasonal Variation in Back Azimuth Residual Black: coherence ≥ 0.5; Gray: coherence < Concave down Concave up?

12 Modeling: Travel Times G2S-07 atmospheric specifications kindly provided by Doug Drob of NRL Predicted seasonal cutoff and time variation of stratospheric arrivals match observations Fractional year

13 Modeling: Back Azimuth Residuals Minimum observed back azimuth residuals are consistent with predictions Observed residuals generally are significantly larger than predictions

14 Modeling: Signal Attenuation Observed signal amplitudes are consistent with a theoretical attenuation model: where r is range, α is an absorption loss value (0.005 for stratospheric return), and C a scaling factor for source size.

15 Modeling: Repeating Arrivals at I10CA G2S-07 cannot match the observed multiple arrivals A model with a faster stratospheric duct and a shallower tropospheric gradient best matches the observed multiple arrivals G2S-07 sound speed (unmodified) Assumed along-path wind Effective sound speed G2S-07 along-path wind Ray fan is broadened Range of bounce points is broadened

16 Conclusions  Repeating detonations at UTTR make excellent atmospheric probes  t shots are commonly detected at ranges of 550 – 1650 km  Detection rates vary seasonally and depend on direction from source  Seasonal variations of celerity and back azimuth are consistent with predictions using G2S-07 specifications  Observations of multiple arrivals imply faster stratospheric duct and shallower tropospheric gradient than specified in G2S-07