Amplitude Modulation of an Acoustic Wave Propagating Near the Sea Surface
Abstract
Sixty Khz CW sound was propagated parallel to and near the ocean surface adjacent to an array of four thermistors, a salinometer, a sound velocimeter, a turbulent velocity probe, and a wave-height probe in order to investigate the statistics and environmental causes of amplitude modulation. The temporal variations of the sound amplitude modulation were studied during four twenty-minute runs over a range of 2 meters at varying depths from near the surface to 14 meters during sea-state one conditions in water of 16 meters-depth. Analysis indicated mean percentage amplitude modulation of approximately 5% with a variance of approximately 10 raised to the -3 power. Temporal correlation times were about 2 seconds except for a 7 second time near the bottom. The power spectral densities of the modulation show strong components corresponding to the predominant ocean wave frequencies as well as higher frequencies that may be attributed to bubble, temperature and/or salinity inhomogeneities. There is evidence that the microstructure dimensions are larger near the bottom than in the upper and middle depths.
Rights
This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.NPS Report Number
NPS-61Md72021ARelated items
Showing items related by title, author, creator and subject.
-
The wavelength dependence of the modulation transfer function of the atmosphere.
Mackin, Jere Gene (Monterey, California. Naval Postgraduate School, 1972-06);An apparatus was designed and constructed to measure the modulation transfer function of the atmospheric medium as a function of wavelength of light. The modulation transfer function (MTF) in this case was considered ... -
Autonomous time-frequency cropping and feature-extraction algorithms for classification of LPI radar modulations
Zilberman, Eric R. (Monterey, California. Naval Postgraduate School, 2006-06);Three autonomous cropping and feature extraction algorithms are examined that can be used for classification of low probability of intercept radar modulations using time-frequency (T-F) images. The first approach, Erosion ... -
Vibration Reduction for Flexible Spacecraft Attitude Control Using PWPF Modulator and Smart Structures
Song, Gangbing; Agrawal, Brij N. (1999);This paper presents a new approach to vibration reduction of flexible spacecraft during attitude control by using Pulse Width Pulse Frequency (PWPF) Modulator for thruster firing and smart materials for active vibration ...