Using matched-field processing to estimate shallow-water bottom properties from shot data taken in the Mediterranean Sea

It is extremely difficult to determine shallow ocean bottom properties (such as sediment layer thicknesses, densities, and sound speeds). However, when acoustic propagation is affected by such environmental parameters, it becomes possible to use acoustic energy as a probe to estimate them. Matched-field processing (MFP) which relies on both field amplitude and phase can be used as a basis for the inversion of experimental data to estimate bottom properties. Recent inversion efforts applied to a data set collected in October 1993 in the Mediterranean Sea north of Elba produce major improvements in MFP power, i.e., in matching the measured field by means of a model using environmental parameters as inputs, even using the high-resolution minimum variance (MV) processor that is notoriously sensitive and usually results in very low values. The inversion method applied to this data set estimates water depth, sediment thickness, density, and a linear sound-speed profile for the first layer, density and a linear sound-speed profile for a second layer, constant sound speed for the underlying half space, array depth, and source range and depth. When the inversion technique allows for the array deformations in range as additional parameters (to be estimated within fractions of a wavelength, e.g., 0.1 m), the MFP MV peak value for the Med data at 100 Hz can increase from 0.48 (using improved estimates of environmental parameters and assuming a vertical line array) to 0.68 (using improved estimates of environmental parameters PLUS improved phone coordinates). The ideal maximum value would be 1.00 (which is achieved for the less sensitive Linear processor). However, many questions remain concerning the reliability of these inversion results and of inversion methods in general.

[1]  S. Glegg,et al.  Comparison between theory and model scale measurements of three‐dimensional sound propagation in a shear supporting penetrable wedge , 1993 .

[2]  Peter Gerstoft,et al.  Inversion of acoustic data using a combination of genetic algorithms and the Gauss–Newton approach , 1995 .

[3]  Peter Gerstoft,et al.  GLOBAL INVERSION BY GENETIC ALGORITHMS FOR BOTH SOURCE POSITION AND ENVIRONMENTAL PARAMETERS , 1994 .

[4]  N. R. Chapman,et al.  Matched field inversion for geoacoustic model parameters using adaptive simulated annealing , 1993 .

[5]  A. Tolstoy,et al.  REVIEW OF MATCHED FIELD PROCESSING FOR ENVIRONMENTAL INVERSE PROBLEMS , 1992 .

[6]  N. R. Chapman,et al.  Matched Field Inversion for Geoacoustic Properties of Young Oceanic Crust , 1995 .

[7]  A. Tolstoy,et al.  ACOUSTIC TOMOGRAPHY VIA MATCHED FIELD PROCESSING , 1991 .

[8]  Michael B. Porter,et al.  BROADBAND SOURCE LOCALIZATION IN THE GULF OF MEXICO , 1996 .

[9]  A. Tolstoy,et al.  SIMULATED PERFORMANCE OF ACOUSTIC TOMOGRAPHY VIA MATCHED FIELD PROCESSING , 1994 .

[10]  Melvin J. Hinich,et al.  Maximum‐likelihood signal processing for a vertical array , 1973 .

[11]  P. Gerstoft,et al.  Inversion for geometric and geoacoustic parameters in shallow water: Experimental results , 1995 .

[12]  C. Harrison Three‐dimensional ray paths in basins, troughs, and near sea mounts by use of ray invariants , 1977 .

[13]  A. Tolstoy,et al.  Linearization of the matched field processing approach to acoustic tomography , 1991 .

[14]  Henrik Schmidt,et al.  Nonlinear inversion for ocean‐bottom properties , 1992 .

[15]  A. Tolstoy,et al.  Experimental confirmation of horizontal refraction of cw acoustic radiation from a point source in a wedge‐shaped ocean environment , 1988 .

[16]  Peter Gerstoft,et al.  Inversion of seismoacoustic data using genetic algorithms and a posteriori probability distributions , 1994 .

[17]  M. Buckingham Acoustic Propagation in a Wedge-Shaped Ocean with Perfectly Reflecting Boundaries , 1984 .

[18]  Michael B. Porter,et al.  Focalization in the Gulf of Mexico , 1996, 1996 IEEE International Conference on Acoustics, Speech, and Signal Processing Conference Proceedings.

[19]  D. E. Weston Horizontal Refraction in a Three-dimensional Medium of Variable Stratification , 1961 .

[20]  H. Bucker Use of calculated sound fields and matched‐field detection to locate sound sources in shallow water , 1976 .

[21]  A. Tolstoy 3-D PROPAGATION ISSUES AND MODELS , 1996 .

[22]  Stan E. Dosso,et al.  Estimation of ocean-bottom properties by matched-field inversion of acoustic field data , 1993 .

[23]  A. Tolstoy Performance of acoustic tomography via matched‐field processing , 1992 .