Acoustic Efficiency Analysis Using Infrasound from NEOs

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Abstract
ReVelle has recently presented a summary of available infrasonic signals from near-earth objects (NEOs) that entered the earth's atmosphere from about 1960–1980. Using an approach developed by Cox we have calculated the acoustic conversion efficiency for a number of these events that were detected by the U.S. Air Force. Based on results with conventional explosions, this quantity is expected to depend weakly on the range from the source. In our analysis of these events, we have used well-known, and independently calibrated, semi-empirical source energy (Es) and wave period at maximum amplitude scaling relations developed by the U.S. Air Force along with various observed signal and atmospheric properties. With this knowledge of the source energy and the range, the efficiency can be computed. Our acoustic efficiencies range typically from about 0.1 to a few percent. In comparison, measurements of thunder by Holmes and co-workers determined an acoustic conversion efficiency from about 0.18 to 0.42 %. Previously, Astapovich also estimated the acoustic efficiency for meteor-fireballs on the basis of only fireball sound reports from a single event and determined a value of ⩽ 0.01 %. Using the efficiencies derived from analysis of the Air Force data, we hope eventually to predict the detection rate of NEOs for the proposed global scale CTBT (Comprehensive Test Ban Treaty) infrasonic system (60 arrays, each of 4 elements) and to establish the expected false alarm rate for such sources.

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