ACOUSTIC DETECTION OF HIGH - ALTITUDE TURBULENCE
Abstract
Background noise at frequencies from 0.2 to 200 cps was monitored with free-floating, balloon-borne acoustic probes at altitudes of 55,000 to 73,000 feet. Spectrograms, signatures, cross-correlations, and probability-density curves were obtained from the data. The noise has a spectrum with 6 db/octave negative slope, is acoustic and Gaussian, and is time-steady for periods of several hours, although noise pressures from 0.03 to 1 dyne/sq. cm were measured on different days. These and other results indicate that the noise comes from lower altitudes and is produced by an array of statistically independent radiators, such as turbulent eddies. A theory for the power spectrum of noise radiated by turbulence is cited, and the predicted spectrum is compared to the experimental results. Other possible sources of high-altitude acoustic noise are described. Descriptions and illustrations of the instruments used to acquire and process the experimental data are presented.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 1964
- Accession Number
- AD0434705
Entities
People
- John W. Wescott
Organizations
- University of Michigan