Tomographic observation of shallow-water inhomogeneities in the case of probing by a focused high-frequency acoustic field. I. Structure of simulation model

Abstract

UDC 534.26We study the possibilities of acoustic tomography observation of small-size bodies in shallow-water layered oceanic waveguides within the framework of geometric acoustics. For increasing the spatial resolution and sensitivity in the considered inverse problem, we used the waveguide-matched focusing of the received and radiated fields into the region of expected location of the observed body. The algorithm of observation in this case consists of search for a global extremum of decision statistics, which is determined by the difference between the measured data and the hypothetic body location. Such hypotheses are formed on the basis of a priori information in the form of the waveguide model and the data on the structure of the observation system. For decreasing the influence of noise associated with the interference of fields in the waveguide, selection of separate tomographic ray projections with the subsequent incoherent accumulation of partial images is used. A tomographic shallow-water observation model based on such principles is analyzed.

Tomography in observation of inhomogenenities in shallow sea during sounding by a focused high-frequency acoustic field: II. Study of the observation efficiency

“…For high-frequency sounding of shallow sea, the structure of the sounding signals can also be optimized by minimizing the radiation along the rays incident on the bottom and the scattering irregular sea surface [5,8]. The predominant excitation of individual modes and the simultaneous suppression of other ones can be implemented using a vertical radiating array whose parameters (including the distribution of the aperture factors) are sought by solving the corresponding optimization problems [9].…”

“…Unlike a similar problem for low-frequency radiating arrays, the optimal excitation of the ray fields depends on the position of the region in which the high intensity of the sounding field should be ensured. In this case, the formation of the necessary amplitude-phase field distributions within the apertures of the radiating and receiving arrays also ensures the compensation for the focusing effect of the waveguide [8][9][10].…”

“…The analysis performed in [6][7][8] indicates that such a regularization can be implemented using a priori information in the form of a simulation model of the observation. The components of such a model include models of the waveguide, propagation and scattering of the high-frequency field, the observation system, the observed body, the concurrent randomly distributed inhomogeneities (scatterers of the sound), and independent (additive) noise [6][7][8][9][10][11][12][13][14][15][16][17]. Using such a system in the general case and calculating statistical distributions of the useful signals, and the noise and reverberation signals for particular observation conditions, it is possible to estimate the inverse-problem parameter regions in which the given accuracy of the observations can be ensured [6,7].…”

“…The parameters of the observed inhomogeneities are also estimated using the simulation model which is applied for the statistical check of the hypotheses on the parameters of the observed inhomogeneities. The values for which the decision statistic satisfies the reliability criteria are taken as the problem solution [7,8,14].…”

“…The system is based on the use of ray structures matched to the waveguide and is studied using a simulation model of the observation, which was developed in [8]. The structure of the object image in shallow sea is analyzed for both different individual tomographic projections and a superposition of the results for individual projections.…”