Accession Number : ADA112431

Title :   20 KHz Acoustic Fluctuations Due to Thermal Finestructure in the Upper Ocean.

Descriptive Note : Master's thesis,


Personal Author(s) : Wakeman,Mark

PDF Url : ADA112431

Report Date : Dec 1981

Pagination or Media Count : 86

Abstract : The Acoustic Variability Experiment measured acoustic pulses which travel a wholly refracted (400m) path between a source and receiver in the upper ocean. The 20 KHz pulse travel times had rms variations between 1 and 60 microseconds, calculated over each half hour sample period, and corresponding pulse amplitude fluctuations between 3% and 14%. The temporal and spatial structure of the temperature field were measured simultaneously with the acoustic transmission. A spectrum of a 15-day temperature record showed the presence of inertial and tidal motions, and internal waves at higher frequencies. Microstructure was intermittent and appeared to be associated with internal waves. The temperature integral scales calculated from the spatial autocorrelation functions ranged from 1.2 to 14m (est) in the vertical and from 3.4m to greater than 50m (est) in the horizontal. A comparison of the measured acoustic amplitude variance with temperature variance and scale lengths measured at the receiver station showed poor correlation using the theoretical models of Chernov and Debye.

Descriptors :   *Sound transmission, *Temperature, *Ocean environments, Underwater sound signals, Pulse amplitude, Variations, Temperature gradients, Time intervals, Inertia, Ocean tides, Internal waves, Frequency, Microstructure, Refractive index, Autocorrelation, Spatial distribution, Wave propagation, Receivers, Stations, Measurement, Theses

Subject Categories : Physical and Dynamic Oceanography

Distribution Statement : APPROVED FOR PUBLIC RELEASE