Computer Science – Sound
Scientific paper
Nov 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999m%26ps...34..995r&link_type=abstract
Meteoritics & Planetary Science, vol. 34, no. 6, pp. 995-1005 (1999).
Computer Science
Sound
18
Scientific paper
During the early morning hours of the night of the peak of the annual Leonid meteor shower on November 17, 1998, a bright fireball (~ -12--14 visual magnitude at 100 km in the zenith) was observed over Northern New Mexico with visual sightings as far away from Los Alamos as Albuquerque (~150 km to the south of Los Alamos), including direct persistent trail observations at the USAF Starfire Optical Range (SOR), which is also near Albuuqerque. This event did not produce any sonic boom reports presumably because of the its high altitude. It was also detected locally by an infrared radiometer at Sandia National Laboratory and by an intensified CCD camera located in Placitas, New Mexico. Subsequent investigations of the data from the six infrasound arrays used by LANL (Los Alamos National Laboratory) and operated for the DOE (Department of Energy) as a part of the CTBT (Comprehensive Test Ban Treaty) Research and Development program for the IMS (International Monitoring System) showed the presence of an infrasonic signal from the proper direction at the correct time for this bolide from two of our six arrays (both located in Los Alamos). The infrasound recordings, i.e., the wave amplitude and period data, indicated that an explosion occurred in the atmosphere at a source height of about ~93.5 km, having its origins slightly to the north and west of Los Alamos. Purely geometric solutions from the ground observers reports combined with direct measurements from the CCD camera at Placitas produced a source height of 91 +/- 7 km. The signal characteristics analyzed from 0.10 to 3.0 Hz, include a total duration of ~ 3 - 4 sec for a source directed from Los Alamos toward 353.6 +/- 0.3 deg measured from true north at a maximum elevation arrival angle of ~ 72.7 degrees. The latter was deduced on the basis of the observed signal trace velocities (for the part of the recording with the highest cross-correlation) and ranged from a constant value of ~920-1150 m/sec (depending on the window length used in the analysis) for a ray trajectory along a direct refractive path between the source and the Los Alamos arrays. The dominant signal frequency at maximum amplitude at Los Alamos was about 0.71 Hz. These highly correlated signals had a peak to peak, maximum amplitude of ~2.1 microbars (0.21 Pa). Our analysis, using several methods that incorporate various observed signal characteristics, total distance traveled, etc., indicates that the bolide probably had a source energy of ~ 1.14 tons (TNT equivalent) or 4.77(10(9) joules. This is ~14.1 times smaller than the source energy estimate made using the infrasonic, empirical source energy relationship for low altitude stationary point sources developed in the 1960's by AFTAC (Air Force Technical Applications Center, Patrick AFB, Florida). This relation was originally developed however for much larger source energies and at much longer ranges.
ReVelle Douglas O.
Whitaker Rodney W.
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