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The results of mathematical model measurements of the speed of the transverse current in the Fram Strait are presented. The method is based on the statistical processing of the propagation time fluctuations of the probing signals along 16 acoustic tracks. The dependence of the sound velocity on depth is assumed to correspond to winter conditions. For the imitation of the current, the three-dimensional field of environmental inhomogeneities observed in the strait is computed. The complex profile of the current in the direction across the strait is represented by the motion of 10 layers of this field that move with different velocities. The measuring system consists of four transmitters and four receivers positioned near both coasts of the strait. The rays used for the measurements do not touch the bottom and do not change their type under the effect of environmental inhomogeneities crossing the acoustic tracks. [ABSTRACT FROM AUTHOR]

The horizontal refraction method (HRM) of transverse current acoustics monitoring in the Fram Strait environment is modeled numerically. The current profile was constructed on the basis of experimental data on the West Spitsbergen Current (WSC) structure and the complex environment of the region presented by the sound speed profiles, which were derived from the experiments. The HRM is based on the measurements of the deflection of the horizontal modal rays due to the gradient of the refraction index produced by the transverse current. The signals received by the antennas in a receiving plane perpendicular to the propagation axis have a modal phase difference in proportion to the average transverse velocity, which is due to the different orientation of the acoustical path of the current. The interesting result is that even in a strong mode coupling environment the numerically obtained phase difference is quite close to its value as calculated by adiabatic approximation. The physical reason behind this is most likely that the mode coupling impact can be canceled at the sound signal propagation along the two very close paths. [ABSTRACT FROM AUTHOR]

The transverse flow of inhomogeneous fluid produces fluctuation of the acoustic signal passing through it. The coherence of frequency-spaced signal fluctuation is related to the advection of the inhomogeneous medium through the sound path, thus providing a basis for the current velocity measurement. This method can be considered to be the 'frequency-domain' version of the conventional scintillation approach to the current velocity registration based on the measurement of the signal correlation transmitted from the source to the two separated in space receivers (space-domain scintillation) [S. Clifford and D. Farmer, J. Acoust. Soc. Am. 74, 1826-1832 (1983)]. The sensitivity of the method depends on the features of the ocean fine structure, which is determined mainly by the internal waves and turbulence. To estimate the sensitivity of the multifrequency method of transverse current probing, the coherence function of two signals propagating through a frozen and moving internal wave field and through the turbulence is considered. The application of the multifrequency signal allows estimation of the fine-structure parameters as well as the current velocity. © 2001 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

Ocean acoustic tomography based on modal horizontal refraction/phase difference measurement has been developed in recent years. In this paper, potential opportunities for remotely sensing various interesting ocean dynamic structures by using the modal-horizontal-refraction tomography and modal-phase tomography are discussed, including: (1) retrieval of the 3-D structure of a mesoscale eddy, (2) monitoring of the transverse component of the current, (3) retrieval of ocean frontal parameters, and (4) acoustically diagnosing internal solitary waves (ISW) in the coastal zone. [ABSTRACT FROM AUTHOR]

Nonlinear propagation of finite-amplitude acoustic pulse in water and through a sample of water-saturated granular medium is considered. To generate high-intensity acoustic pulses laser generation of sound was used. The region of fluid perturbed by the laser acts as a volume-distributed source. In a fluid with weak light attenuation, a cylindrical source could be formed by a narrow laser beam. The nonlinear distortion of the cylindrical finite-amplitude wave in water is investigated. The measured rate of distortion corresponds to that calculated in the approximation of nonlinear acoustics. In a strongly light-absorbing medium, a wide (compared to the typical sound wavelength) laser beam produces a circular planar source. Such a source produces acoustical pulses of amplitude up to 3 MPa and duration about 1 μs in different fluids. This source was used to investigate the propagation of high-intensity wide frequency band sound signals in a sample of water-saturated cobalt-manganese crust (CMC). Specific acoustical features of the crust such as nonlinear sound pulse distortion and the frequency dependance of attenuation, varying with the amplitude, are considered. Theoretical interpretation of the results is given. © 1999 Acoustical Society of America. [ABSTRACT FROM AUTHOR]

The method of describing the propagation of finite-amplitude waves based on the introduction of coordinates 'accompanying' the wave system is used for the consideration of the radiation of a compression wave by a sphere that is expanding at a constant rate in a perfect medium. To estimate the degree of accuracy of this method, the results are compared with the exact solution of G. I. Taylor. [Proc. Roy. Soc. (London) A186, 273-292 (1946)]. [ABSTRACT FROM AUTHOR]

The propagation of the finite-amplitude waves is considered in this paper, mainly with the help of the method based on the introduction of the 'accompanying' system of coordinates. The distortion of the initially harmonic wave and its attenuation is described and some remarks on nonlinear effects in high-intensity ultrasonic focusing systems are given. The propagation of a nonperiodical compressional wave that is radiated by an expanding sphere is considered also. [ABSTRACT FROM AUTHOR]