BLANK NOT FILMED s 1 9 ATMOSPHERIC SOUND PROPAGATION Richard

The propagation of sound waves at infrasonic frequencies (oscillation periods 1.0 1000 seconds) in the atmosphere is being studied by a network of seven stations separated geographically by distances of the order of thousands of kilometers. One of the typical stations, in Washington, D. C., has an array of five microphones separated by distances of about 7 kilometers. Each microphone is at ground level and is connected to the central station by means of a leased telephone line. In effect the array is "steered" to look for sound waves in a programmed sequence of search directions. The station measures the following characteristics of infrasonic waves passing through Washington: (1) the amplitude and waveform of the incident sound pressure, (2) the direction of propagation of the wave, (3) the horizontal phase velocity, and (4) the distribution of sound wave energy at various frequencies of oscillation. Some infrasonic sources which have been identified and studied include the aurora borealis, tornadoes, volcanos, gravity waves on the oceans, earthquakes, and atmospheric instability waves caused by winds at the tropopause. Waves of unknown origin seem to radiate from several geographical locations, including one in the Argentine. 633 https://ntrs.nasa.gov/search.jsp?R=19720017735 2018-04-02T12:11:32+00:00Z