Doutt James A.

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Doutt
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James A.
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1981 - 1986 2
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  • Technical Report
    Bottom interaction of low-frequency acoustic signals at small grazing angles in the deep ocean
    (Woods Hole Oceanographic Institution, 1981-07) Frisk, George V. ; Doutt, James A. ; Hays, Earl E.
    The results of a deep-ocean bottom interaction experiment are presented in which the effects of both bottom refraction and subbottom reflection were observed. Data were obtained in the Hatteras Abyssal Plain using a deep towed 220-Hz pulsed cw source and two receivers anchored near the bottom. For ranges between 1 and 6 km, corresponding to bottom grazing angles less than 13°, the quadrature components of the received signals were recorded digitally. The observed amplitude shows a strong spatial interference pattern which is composed of the direct and bottom interacting arrivals. It is shown that for small source-receiver separations, the bottom return is dominated by a strong subbollom reflection. With increasing separation, this arrival evolves into a refracted arrival due to the presence of a positive sound-speed gradient in the sediment overlying the subbottom. Because of the gradient, a caustic is formed, and corresponding high intensity regions are observed in the data at the expected ranges. Values of sediment layer thickness, sound-speed gradient, and sound-speed drop at the water-bollom interface are obtained from best fits to the data using ray theory, normal mode theory, and the parabolic equation method. These values are consistent with those obtained in nearby locations by other workers. The success of the parabolic equation method indicates that at small grazing angles, the bottom interaction process may be modeled as a propagation process combined with the effect of a perfect, soft subbollom reflector. A value of sediment attenuation, 0.0015 dB/mat 220Hz, is also inferred from the data and is among the lowest values reported to date in the literature.
  • Technical Report
    Short-term variability in nighttime scattering strength levels at one site in the eastern Algero-Provençal Basin
    (Woods Hole Oceanographic Institution, 1986-03) Doutt, James A.
    A sequence of nine nighttime, broadband volume scattering strength measurements obtained in 1973 over a period of approximately one hour was used to study the short-term variability of scattering strength in 100 Hz bands over frequencies ranging from 100 Hz to 24 kHz and depths ranging from 400 meters to 1000 meters. The variability was found to be independent of depth and was least in the frequency range three kHz to eight kHz where the standard deviation was approximately four dB less than the mean level, Outside this frequency range the standard deviation was somewhat greater than the mean level.