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Abstract:
Acoustic background noise at the earth's surface for frequencies from 0.2 to 100 cps was monitored outdoors with two low-frequency condenser microphones placed 1500 feet apart. The wind speed at each microphone was monitored with cup anemometers. Data were transmitted by microwave links to a central receiving station and recorded on magnetic tape. The acoustic data were preemphasized 6 db/octave before transmission to improve signal-to-noise ratios. Oscillograms of the multichannel acoustic data show cross correlations by visual inspection for the sounds radiated from upper-air turbulence and aircraft. Oscillograms of noise generated locally by surface winds show no apparent cross-correlation. Details of instrumentation are presented. These include a block diagram of the detection, data-link, and recording system and circuit diagrams of components developed for it. A pistonphone calibrator with pushbutton frequencies from 0.125 to 30 cps is described, and its use for amplitude and phase calibration of microphones is explained.
| Limitations: |
 APPROVED FOR PUBLIC RELEASE |
| Description: |
Final rept. |
| Pages: |
40 |
| Report Date: |
FEB 1963 |
| Contract Number: |
DA20018ORD22840 |
| Report Number: |
0738504 |
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