BORN-TYPE SCHEMES FOR THE ACOUSTIC PROBING OF 1-D FLUID MEDIA FROM TIME-HARMONIC PLANAR REFLECTION COEFFICIENTS AT 2 INCIDENCES

The probing of a 1-D (depth-) inhomogeneous fluid half-space is carrie d out fr om a limited knowledge of plane-wave reflection coefficients with respect to frequency at two precritical incidences. Born-type inv ersion algorithms are investigated. First, index profiles as a functio n of a density-dependent pseudodepth are retrieved at two incidences; then density and speed-of-sound profiles versus depth are extracted. A Born-iterative scheme builds up the solution as the limit of a sequen ce of solutions of approximate, constrained linear problems. A Born-ex tended scheme directly yields a linearized solution. Two variants of t he Born-iterative scheme are developed, the first one when data are kn own in both amplitude and phase, the second one with amplitude-only da ta. Possible-but not limiting-applications are in underwater acoustics , once the planar reflection coefficient of a seabed has been found, e .g., from the depth-dependent Green's function in the spectral domain. Numerical simulations illustrate the schemes. Good index profiles are obtained with reasonable behavior versus noise or other causes of lim itations. As is expected, separate probing of speed and density profil es remains difficult. The computationally costly exact scheme is not b etter than the cheaper approximate one when good data are available, b ut handles more complicated situations. (C) 1996 Acoustical Society of America.