|Article title||THE PROBLEMS OF REMOTE DETERMINATION OF HYDROPHYSICAL CHARACTERISTICS OF THE MARINE ENVIRONMENT BY METHODS OF NONLINEAR ACOUSTICS|
|Authors||G. N. Seravin, I. I. Mikushin, S. P. Tarasov|
|Section||SECTION IV. COMMUNICATIONS, NAVIGATION AND HOMING|
|Month, Year||01, 2018 @en|
|Index UDC||551.463.224: 534.222|
|Abstract||The problem of determining the hydrophysical characteristics of the marine environment from the recorded values of known emitted and received reflected acoustic signals from natural lenses in the marine environment, without directly measuring the characteristics themselves by means of ship-based submersible probes, is currently particularly relevant. The impact of the vertical sound velocity distribution (VSVD) from the surface to the bottom in a sea waveguide is assessed immediately prior to the use of various hydroacoustic equipment installed on a vessel, or on autonomous uninhabited underwater apparatus. The possibility of using the information on hydrophysical characteristics of waveguide propagation of hydroacoustic signals, when detected are the underwater targets, can significantly improve the efficiency of use of shipboard sonar equipment. Research and development of remote methods for measuring the vertical sound velocity distribution (VSVD) with the help of so-called parametric arrays, which principle of operation is based on the nonlinear interaction of acoustic waves in the marine environment. The possibilities of using two nonlinear effects for measuring the vertical velocity distribution of sound by a remote method are considered. The analysis of the possibility of using sound scattering on sound for remote determination of the vertical velocity distribution of sound is analyzed. The energy relationships have shown that the signal of the difference frequency, scattered from the region of intersection of acoustic beams, can in principle be reliably accepted. To solve the inverse problem, the algorithm of the reconstruction of the desired VSVD is used by the method of discretization. The approximation of the required function by segments in an aqueous medium is presented, represented in the form of layers with constant vertical gradients of the sound velocity. The possibility of determining the VSVD on the basis of the secondary effect of phase modulation of pump waves by a difference-frequency wave is analyzed. To isolate the phase, it is necessary to filter out the signal with the combinational frequency at the output of the antenna from the total high-frequency electrical signal and to generate a reference electric signal with the same frequency. The signals are fed to the corresponding inputs of the phase meter, at the output of which there will be an electrical phase signal, which is digitized and enters the computational block. The errors of the method are considered. It is noted that a rather significant amount of error does not allow us to consider the method of determining the VSVD based on the secondary effect of phase modulation of pump waves by a wave of difference frequency, as a promising tool for the introduction of measurements into practice. The possibility of practical implementation of the proposed methods is considered.|
|Keywords||Sound velocity; remote method; nonlinear interaction; acoustic waves; vertical sound velocity distribution.|
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