Locating Bolide Fragmentations and Terminal Explosions using Arrival times of Acoustic Waves Wayne N. Edwards and Alan R. Hildebrand Department of Geology & Geophysics, University of Calgary, Alberta, Canada 2003 AGU Infrasound Technology Workshop October 29 th, 2003

What is a Supracenter? Analogous to earthquake location in the solid Earth Analogous to earthquake location in the solid Earth Complications Complications P wave velocities slower P wave velocities slower Winds vary in magnitude & direction with altitude Winds vary in magnitude & direction with altitude Fireball explodes – point source of finite duration Fireball explodes – point source of finite duration Wavefront propagates to ground where seismometers, microphones & infrasound arrays record its arrival Wavefront propagates to ground where seismometers, microphones & infrasound arrays record its arrival Photo by: Brad Gledhill

Potential Arrivals depend on distance of receiver station Potential Arrivals depend on distance of receiver station a. Direct arrivals b. Ducted waves c. Thermospheric returns d. Stratospheric returns e. Skips (Brown et al. 2003) Red Box shows region of direct arrivals Propagation in the Atmosphere

Recognizing the Seismic Signal Duration: order of minutes long Propagation: low trace velocities across arrays A – Slow initial rise – ground roll arrivals B – Prominent peak – direct atmospheric – Terminal Burst or Sonic Boom? C – Long drawn out tail – higher altitude sources e.g. Early fragmentation e.g. Early fragmentation A B C

Finding a Solution 1 – Identify & pick station arrival times 2 – Construct model atmosphere  Acoustic velocity 3 – Assume that all arrivals from the same event: T A = T B = T C = T D = … = T b = Initial time of burst

Finding a Solution 5 – Choose a position: ray trace to receivers 6b – Use a known, observed occurrence time Earth-observing satellitesEarth-observing satellites Recorded videoRecorded video (Nelson & Vidale 1990) 6a – Find the mean time of occurrence 7 – Calculate station traveltime residuals 8 – Vary position to minimize the mean residual

Previous Supracenter Locations Have only treated atmosphere as an isotropic velocity medium. Have only treated atmosphere as an isotropic velocity medium. Johnston 1987: Missile silo explosion & supersonic aircraft Johnston 1987: Missile silo explosion & supersonic aircraft Qamar 1995: Fireball terminal bursts Qamar 1995: Fireball terminal bursts Borovička and Kalenda 2003: Fireball fragmentation Borovička and Kalenda 2003: Fireball fragmentation Assumed atmosphere is static in most cases Assumed atmosphere is static in most casesResult: Solutions may mis-locate an event by several kilometers depending upon wind conditions in the atmosphere at the time of the event.

Ray Tracing Complications Winds  Ray propagation becomes direction dependant Winds  Ray propagation becomes direction dependant Winds perpendicular to azimuth add motion outside of azimuth plane RESULT: rays bend! Winds perpendicular to azimuth add motion outside of azimuth plane RESULT: rays bend! Azimuth & Elevation angle UNKNOWN Azimuth & Elevation angle UNKNOWN Solution: Solution: Modified Tau-p Equations Modified Tau-p Equations (Garcés et al. 1998) Iteratively refining “Ray Net” Iteratively refining “Ray Net” to identify ray orientation to identify ray orientation angles connecting source angles connecting source to receiver to receiver

Structure of Traveltime Error (Ray tracing vs. Analytic) 30 km Source in a windy, (45 m/s from the North) Isotropic (300 m/s) Atmosphere (15% of Local Sound Speed or L.S.S.) Maximum Error: ~0.0048% of Traveltime Analytic Model

The SUPRACENTER Program Uses a stratified model of the atmosphere Uses a stratified model of the atmosphere Local or nearby radiosonde soundings Local or nearby radiosonde soundings Atmospheric models (e.g. MSIS-E, HWM) Atmospheric models (e.g. MSIS-E, HWM) 1978 U.S. Standard Atmosphere (as option) 1978 U.S. Standard Atmosphere (as option) Includes the effects of winds as it traces rays! Includes the effects of winds as it traces rays! NOT a correction for wind applied after locating an otherwise static solution. NOT a correction for wind applied after locating an otherwise static solution.

Simplifications & Assumptions Geometrical rays Geometrical rays - diffraction is minimal over the travel time of a ray Atmospheric motions are predominantly horizontal Atmospheric motions are predominantly horizontal - (i.e. vertical motions are negligible) Horizontal variations in temperature and wind Horizontal variations in temperature and wind are negligible. are negligible. Atmosphere is approximated by discrete layers, Atmosphere is approximated by discrete layers, each with its own characteristic temperature and each with its own characteristic temperature and wind vector. wind vector. Use only direct air arrivals. Use only direct air arrivals. (i.e. receivers ≤ 100 km to the event epicenter) (i.e. receivers ≤ 100 km to the event epicenter) Flat Earth Approximation Flat Earth Approximation

Testing SUPRACENTER … El Paso Superbolide, October 9 th El Paso Superbolide, October 9 th Mt. Adams Fireball, January 25 th Mt. Adams Fireball, January 25 th Movávka meteorite fall, May 6 th Movávka meteorite fall, May 6 th Three seismically detected fireball events were chosen where independent solutions existed. Two Historical: One Recent:

Case Study #1: El Paso Superbolide October 9 th, 1997 Daytime fireball at local noon hour ~18:47:15 UT Daytime fireball at local noon hour ~18:47:15 UT Many eyewitnesses Many eyewitnesses 19 photographs of the dust cloud 19 photographs of the dust cloud 6 video recordings 6 video recordings 8 seismic detections & 2 infrasonic 8 seismic detections & 2 infrasonic Terminal burst of fireball produced a circular dust cloud ~1 km in diameter  supersonic shock Terminal burst of fireball produced a circular dust cloud ~1 km in diameter  supersonic shock Photographic observations produced an accurate determination of the position for the terminal explosion. (Hildebrand et al. 1999) Photographic observations produced an accurate determination of the position for the terminal explosion. (Hildebrand et al. 1999)

Distribution of Stations Non-ideal linear orientation (NW-SE) Non-ideal linear orientation (NW-SE) Long distances between stations Long distances between stations  Limited # of potential stations with direct arrivals

Atmospheric Sounding Radiosonde Data largest winds at ~15 km where local sound speed is lowest largest winds at ~15 km where local sound speed is lowest winds predominantly from WSW below 20 km winds predominantly from WSW below 20 km prominent wind shearing at ~30 km prominent wind shearing at ~30 km

Comparison of Solutions Hildebrand et al. (1999) Hildebrand et al. (1999) Observed Event time ~18:47:15 UT Observed Event time ~18:47:15 UT o N, o W at ~28.5 km altitude o N, o W at ~28.5 km altitude Derived from eyewitness reports, photographic and video records Derived from eyewitness reports, photographic and video records SUPRACENTER SUPRACENTER o N, o W at 27.6 km a.s.l km shock o N, o W at 27.6 km a.s.l km shock Occurrence time constrained to 18:47:15 UT Occurrence time constrained to 18:47:15 UT Avg. residual of seconds Avg. residual of seconds ~2.1 km WSW from Hildebrand et al. solution found through independent methods ~2.1 km WSW from Hildebrand et al. solution found through independent methods

N

Case Study #2: Mt. Adams Fireball January 25 th, Bright Daytime fireball at local noon hour. 12:51 pm, Pacific Standard Time Bright Daytime fireball at local noon hour. 12:51 pm, Pacific Standard Time NW to SE track over Puget Sound, Washington ending near the NW flank of Mt. Adams (Pugh 1990). NW to SE track over Puget Sound, Washington ending near the NW flank of Mt. Adams (Pugh 1990). During decent fireball split in two with each fragment producing its own terminal burst. During decent fireball split in two with each fragment producing its own terminal burst. Both bursts were recorded by 26 seismic stations (Qamar 1995) of the Pacific Northwest Seismic Network. Both bursts were recorded by 26 seismic stations (Qamar 1995) of the Pacific Northwest Seismic Network.

January 25 th, 1989 Model Atmosphere Radiosonde Data U.S. Std Atmosphere + HWM - dual temperature inversions - increased winds correlate to region of lowest temperature - Predominantly NNW winds

Comparison of Solutions Qamar (1995) Qamar (1995) Burst A: o N, o W at 35.1 ± 1.0 km 20:51:10.1 UT Burst A: o N, o W at 35.1 ± 1.0 km 20:51:10.1 UT Burst B: o N, o W at 30.4 ± 0.7 km 20:51:10.9 UT Burst B: o N, o W at 30.4 ± 0.7 km 20:51:10.9 UT SUPRACENTER SUPRACENTER Burst A: o N, o W at km 20:51:14.5 UT Burst A: o N, o W at km 20:51:14.5 UT Avg. residual: sec. Stations Untimed: 5 Avg. residual: sec. Stations Untimed: 5 ~2.7 km NNW of Qamar’s solution ~2.7 km NNW of Qamar’s solution Burst B: o N, o W at km 20:51:15.1 UT Burst B: o N, o W at km 20:51:15.1 UT Avg. residual: sec. Stations Untimed: 5 Avg. residual: sec. Stations Untimed: 5 ~2.5 km NNW of Qamar’s solution ~2.5 km NNW of Qamar’s solution

Differences? Low winter atmospheric temperatures Low winter atmospheric temperatures lower sound speeds lower sound speeds bursts at lower heights  later times bursts at lower heights  later times Without independent measure of fireball’s time of occurrence, determination of which is correct event time is unlikely to be resolved Without independent measure of fireball’s time of occurrence, determination of which is correct event time is unlikely to be resolved

Mt. Adams Fireball Trajectory Trajectory Parameters: Azimuth: 152 o Elevation: 43 o Velocity: 11.7 km/s Consistent with investigation of Pugh (1990): “Entered atmosphere over Puget Sound … disruption over northwest flank of Mt. Adams”

Conclusions 1.Using arrivals of acoustic waves at the surface and realistic ray tracing it is possible to locate atmospheric explosions. 2.Significant position “drift” does occur when strong unidirectional winds are present. 3.Position “drift” can be on the order of several kilometres  width’s of meteorite strewn fields 4.Method is independent of the time of the fireball 5.SUPRACENTER demonstrates both consistency with and improvement over the simple isotropic (average velocity) atmosphere treatments of the past.

Implications Potential for 24 hr monitoring for fireballs Potential for 24 hr monitoring for fireballs More monitoring stations needed More monitoring stations needed Simple as installing a microphone + recorder on current & future fireball camera networks Simple as installing a microphone + recorder on current & future fireball camera networks How does this help meteorite recovery efforts? How does this help meteorite recovery efforts? Better estimates for locations of potential strewn fields Better estimates for locations of potential strewn fields Potential recovery of more freshly fallen meteorites Potential recovery of more freshly fallen meteorites Another tool for fireball trajectory tracking Another tool for fireball trajectory tracking Accurate location  Constrain energy calibrations Accurate location  Constrain energy calibrations

Future Work Extension of supracenter location method to stratospheric and thermospheric returns Extension of supracenter location method to stratospheric and thermospheric returns Allow distant stations to be used in solution Allow distant stations to be used in solution Provide more constraint to poorly sampled events Provide more constraint to poorly sampled events Requirements: Requirements: 1. Choice between multiple arrivals Path that minimizes the station residual Path that minimizes the station residual

References Garcés, M.A., Hansen, R.A. and Lindquist, K., G. (1998) Traveltimes for infrasonic waves propagating in a stratified atmosphere, Geophysical Journal International, 135, pp Hildebrand A., Brown P., Crawford D., Boslough M., Chael E., Revelle D., Doser D., Tagliaferri E., Rathbun D., Cooke D., Adcock C. and Karner J. (1999) The El Paso Superbolide of October 9, 1997, In Lunar and Planetary Science XXX, Abstract #1525, Lunar and Planetary Institute, Houston (CD-ROM). Johnston C. (1987) Air blast recognition and location using regional seismographic networks, Bulletin of the Seismological Society of America, 77, no.4, pp Nelson G. and Vidale J. (1990) Earthquake locations by 3D finite-difference traveltimes, Bulletin of the Seismological Society of America, 80, no.2, pp Nelson G. and Vidale J. (1990) Earthquake locations by 3D finite-difference traveltimes, Bulletin of the Seismological Society of America, 80, no.2, pp Pugh R. (1990) The Mt. Adams, Washington Fireball of January 25, 1989, Meteoritics, 25, p Qamar A. (1995) Space Shuttle and Meteoroid – Tracking Supersonic Objects in the Atmosphere with Seismographs, Seismological Research Letters, 66, no.5, pp

Case Study #3: Morávka Meteorite Fall May 6 th, 2000 Bright daytime fireball observed by 1000’s of eyewitnesses and 3 amateur video’s (Borovička et al. 2003). Bright daytime fireball observed by 1000’s of eyewitnesses and 3 amateur video’s (Borovička et al. 2003). Fireball produced a cascade of individual fragmentations while passing directly over a seismic network. Fireball produced a cascade of individual fragmentations while passing directly over a seismic network. Arrivals for 12 fragmentation events were identified from complex amplitudes and located using an isotropic method by Borovička and Kalenda (2003). Arrivals for 12 fragmentation events were identified from complex amplitudes and located using an isotropic method by Borovička and Kalenda (2003). Both the fireball’s trajectory & pre-fall orbit were well determined through video analysis (Borovička et al. 2003). Both the fireball’s trajectory & pre-fall orbit were well determined through video analysis (Borovička et al. 2003).

Stations & Arrival times 6 of 12 Fragmentation acoustic arrivals identified by Borovička & Kalenda from 11 station records 6 of 12 Fragmentation acoustic arrivals identified by Borovička & Kalenda from 11 station records Atmospheric model of Brown et al. (2003) constructed from a nearby radiosonde release Atmospheric model of Brown et al. (2003) constructed from a nearby radiosonde release (Poprad, Slovakia) (Borovička and Kalenda 2003)

Model Atmosphere to 50 km (Brown et al. 2003) Winds are relatively light m/s (4.4% of L.S.S.) Wind direction is not unidirectional – generally from the South Result: “Wind drift” should be minimal for supracenters

Comparison of Solutions Fit to satellite observed time of 11:51:52.5 UT Fit to satellite observed time of 11:51:52.5 UT Very little wind “drift”: ~0.1 – 1 km Very little wind “drift”: ~0.1 – 1 km Difference between Borovička & Kalenda & SUPRACENTER solutions: 0.4 – 1.5 km Difference between Borovička & Kalenda & SUPRACENTER solutions: 0.4 – 1.5 km Event K: repositioned ~1.5 km to the Southwest Event K: repositioned ~1.5 km to the Southwest Lat. (N) Long.(E)Alt.(km) Long.(E)Alt.(km) CEFGKL Borovička & Kalenda (2003)SUPRACENTER

~1.5 km (2003) C E F G K L

Morávka Fireball Trajectory Trajectory Parameters via SUPRACENTER Azimuth: o Elevation: 18.9 o Determined through Video Analysis (Borovička et al. 2003) Azimuth: o Elevation: 20.4 o Difference? Fragments travelling along slightly different trajectories. or Mis-identification of acoustic arrivals?

Comparison to Kunovice Video Fragmentations show alignment improvement Fragmentations show alignment improvement New K position at start of 1 st stream of fragments New K position at start of 1 st stream of fragments L – misalignment likely due to later occurrence time L – misalignment likely due to later occurrence time Fit L time to ~13 o elevation Fit L time to ~13 o elevation 300 m lower Occ. time: sec.  Fireball Velocity: 22.1 km/s From video analysis: 22.5 km/s (Borovička et al. 2003) NOTE: Small squares: positions of individual fragments mapped from the Kunovice video -300m

References Borovička J., Spurny P., Kalenda P., and Tagliaferri E. (2003) The Mor á vka Meteorite Fall I: Description of the events and determination of the fireball trajectory and orbit from video records, Meteoritics & Planetary Science, In Press. Borovička, J. and Kalenda, P. (2003) Meteoroid dynamics and fragmentation in the atmosphere, Meteoritics and Planetary Science, In Press. Brown P., Kalenda P., ReVelle D., and Borovička J. (2003) The Morávka Meteorite Fall II: Interpretation of Infrasonic and Seismic Data, Meteoritics & Planetary Science, In Press.